August 7, 2009
Brevard Astronomical Society
New Member Packet
M42 Orion Nebula
M51 Whirlpool Galaxy
Brevard Astronomical Society
P.O. Box 1084
Cocoa, FL 32922
M20 Trifid Nebula
Acknowledgements / Credits
Front Cover Astrophotographs:
M42 Orion Nebula & M51 Whirlpool Galaxy
Saturn & Moon
M20 Trifid Nebula
John Powell, BAS Member
Wyck Hoffler, BAS Member
John Small, BAS Member
Throughout this package there are several other astrophotographs which all have been made by the
following BAS Members. Each astrophotographer employs varied techniques to obtain beautiful
photographs of celestial objects.
Pages 3, 14
Pages 7, 11, 13, 15
BAS New Member Packet
Introduction & Section 6: Astronomy Beginners Books
Section 8: Telescope Basics
Edited by Ken Diller, BAS Member
Roy Uyematsu, BAS Member
Stargazing Basics: How to Start Right in Astronomy, by Alan MacRobert,
Reprinted with permission by Sky & Telescope, New Track Media, 2008.
Choosing Your Equipment: How to Choose a Telescope, by Adrian R. Ashford
Reprinted with permission by Sky & Telescope, New Track Media, 2008.
TABLE OF CONTENTS
1 Introduction......................................................................................................................... 3
2 The Brevard Astronomical Society..................................................................................... 4
2.1 Membership .................................................................................................................... 4
2.2 BAS Mission Statement.................................................................................................. 4
2.3 BAS Bylaws.................................................................................................................... 4
2.4 BAS Meeting Date, Time and Location ......................................................................... 5
2.5 BAS Website................................................................................................................... 6
2.6 BAS Officer Elections .................................................................................................... 6
2.7 Contact Info .................................................................................................................... 6
2.8 Friends of BAS ............................................................................................................... 7
2.9 BAS Club Loaner Telescopes......................................................................................... 8
3 Star Parties and Outreach.................................................................................................... 9
3.1 Star Party Etiquette ......................................................................................................... 9
3.2 Star Party Request........................................................................................................... 9
3.3 Star Party Sites / BAS Points of Interest....................................................................... 10
3.4 Outreach........................................................................................................................ 10
3.5 Volunteering ................................................................................................................. 11
4 BCC Planetarium & Observatory ..................................................................................... 12
5 Astrophotography ............................................................................................................. 13
5.1 Astrophotography in Brief ............................................................................................ 13
5.2 How to Submit Photo(s) to BAS Website..................................................................... 14
6 Astronomy Beginner Books.............................................................................................. 15
7 Stargazing Basics: How to Start Right in Astronomy, by Alan MacRobert..................... 16
8 Telescope Basics............................................................................................................... 21
8.1 Definitions..................................................................................................................... 21
8.2 Telescope Types............................................................................................................ 22
8.3 Telescope Suggestions.................................................................................................. 25
8.4 Choosing Your Equipment: How to Choose a Telescope, by Adrian R. Ashford....... 26
9 Useful Links...................................................................................................................... 37
10 Forms ................................................................................................................................ 39
By Roy Uyematsu
Welcome to the world of Astronomy. Astronomy is one of the oldest sciences to be practiced by human
kind. Originally the movements of the stars, Sun, Moon and planets were plotted by ancient civilizations
for religious events and as a calendar to mark events such as planting, or the midsummer solstice. Today
we no longer use this natural calendar but it is the basis for our modern units of time arid measurement of
circles. Ancient astronomers spent countless nights observing the skies with nothing more than some
relatively crude instruments to discover and attempt to describe the night sky. Today’s astronomer, while
using more complicated devices, is walking in the footsteps of those ancients.
Astronomy is unlike many other sciences in one fact: amateurs can and do make significant contributions
to the knowledge base of astronomy. As an amateur astronomer, you can make measurements and
observations that complement those of professionals at observatories, or those using the Hubble Space
Telescope. These include timing of occultations, comet hunting, supernova surveys, eclipse observations,
and variable star observing. All of the previous rely heavily on amateur astronomers for the bulk of the
observations. So if you are interested, there is real science that amateurs can accomplish.
Amateur astronomy, contrary to popular belief, does not require a large outlay of cash to get started. Any
pair of binoculars you may have lying around in a closet is capable of showing you several dozen objects
in the night sky. Purchase of a telescope is not necessary to get started. However, one thing that cannot
be bought for any amount of money is knowledge of the night sky. An amateur astronomer can offset this
knowledge requirement to some extent if they wish to buy computer driven telescopes. So, if you can’t
wait, that option is available, although it will cost more money. Depending on your skills, equipment, and
patience, today’s amateurs can obtain images of the night sky that rival anything accomplished in ground
based observatories. Or you can simply go out and count meteors during a meteor shower. The level of
involvement and commitment is up to you.
This guide is an attempt to acquaint the new member of our club with aspects of the Brevard
Astronomical Society (BAS), amateur astronomy, provide a list of resources for reference, and provide
insight into the purchasing of equipment. The increasing capability of the Internet has been very
beneficial to astronomy. There are several hundred web pages dedicated to many aspects of astronomy,
and countless personal web pages on the subject. So a list of useful popular astronomy links is also
provided at the end of this package.
So welcome to our club, and more importantly, WELCOME TO ASTRONOMY: a lifelong journey to
M17 Omega Nebula Photo by BAS Member John Small
2 The Brevard Astronomical Society
The Brevard Astronomical Society (BAS) is a group of amateur astronomers in Brevard County, Florida.
We are loosely affiliated with the Kennedy Space Center Amateur Astronomers and have several KSCAA
members in our Society.
We are members of the Night Sky Network and the Astronomical League. We are closely associated with
the Brevard Community College Planetarium and Observatory, where we hold monthly meetings as well
as various community outreach events.
Our members have various experiences ranging from beginners, just learning to find bright planets and
major constellations to old geezers with decades of experience in viewing and photographing the heavens.
We use various equipment, from small binoculars to large-aperture, computer-guided telescopes.
The Brevard Astronomical Society is registered with the State of Florida as a not-for-profit corporation.
We are open to the general public in order to foster interest and appreciation of astronomy through all
appropriate means such as public star-observing sessions, presentations, and exhibits. We are eligible for
participation in the service learning program available to BCC students.
2.2 BAS Mission Statement
The BAS exists to encourage the pursuit and enjoyment of astronomy for our
local amateurs and to promote its splendors among the community at large.
2.3 BAS Bylaws
Our bylaws are accessible as a pdf file on the BAS Website listed in Section 2.5 and describe our
governing practices and established membership dues.
2.4 BAS Meeting Date, Time and Location
BAS Membership Meetings, with a featured speaker on matters of astronomy, are held at 7:00 PM on the
third Wednesday of each month, except December, at the Brevard Community College Planetarium,
Classroom, or Theater located in Cocoa. All three rooms are located in the same building and are used
based on availability and meeting agenda. Most meetings are held in the classroom. When available, past
presentations may be accessible on the BAS Website. Members are also encouraged to consider giving a
presentation of an astronomy or space related topic that interests them. Let a BAS Officer know if you
have an interest in this. The meeting setting is friendly and cordial, and you are among friends.
Visitors are always welcome to attend!
Astronaut Memorial Planetarium and Observatory
Brevard Community College (BCC)
1519 Clearlake Rd
Cocoa, FL 32922
Directions to the BCC Cocoa Campus are as follows along with a map to the facility:
From North and West:
From the intersection of U.S. 1 and 528 (Beachline) go South on U.S. 1 to the first traffic signal at
Michigan Avenue. Turn right on Michigan and go to the first traffic signal at Clearlake Road. Turn left
and go to the first traffic signal at Rosetine Street. Turn right and go about a half mile. As you pass
between baseball fields on the left and tennis courts on the right with High School fields ahead, you
should see the BCC Planetarium sign on your right. Turn right and go straight back as far as you can.
Park anywhere near the big science-fiction style building and walk to the door nearest the lake. That's us!
From the intersection of I-95 and 520 go East on 520 to Clearlake Road. Turn left and go North on
Clearlake to Rosetine. Turn left and go about a half mile. As you pass between baseball fields on the left
and tennis courts on the right with High School fields ahead, you should see the BCC Planetarium sign on
your right. Turn right and go straight back as far as you can. Park anywhere near the big science-fiction
style building and walk to the door nearest the lake. That's us!
Enter Campus Here
2.5 BAS Website
Learn more about the BAS structure, activities and membership by accessing the BAS Website listed
At the BAS Website there are navigation links to BAS specific subjects listed below, along with many
other various astronomy and space related sites accessible under the “Links” path. The current links are
reprinted at the end of this package for your immediate reference also.
2.6 BAS Officer Elections
BAS Website Navigation Links
• Home • Brevard Weather
• About BAS • Our Advantage
• Star Parties • Light Pollution
• Monthly Meetings • Newsletter
• BAS Telescopes • Astronomical League
• Mirror Making Course • Astronomy Glossary
• Presentations • Contact BAS
• Events Calendar • Links
• Photo Albums • Search BAS website
In accordance with BAS bylaws, registered members elect officers for President, Vice-President, and
Secretary for one year terms each. The Treasurer position is a two year term, thus this position is elected
once every two years. Elections are held at the monthly December meeting and All BAS members are
eligible, and encouraged, to vote.
The December meeting is typically held at a local restaurant for dining and socializing in addition to
elections and awards. This information is discussed and disseminated to all members prior to the
December meeting and elections.
2.7 Contact Info
• Individual BAS Officers may be contacted with the following email addresses:
• The following general email address may also be used to contact the BAS:
• The “Outreach Coordinator” discussed in Section 3.4 of this packet can also be reached at:
• For letter correspondence, the BAS Mailing address is:
• BAS Email Forum:
Brevard Astronomical Society
P.O. Box 1084
Cocoa FL 32922
An email forum for those BAS members who choose to be included, provide a means to
communicate via internet with each other about topics concerning astronomy and space
exploration. Information about star parties, meetings, astrophotography, volunteer requests, and
upcoming NASA launches are just a few of the topics typically addressed.
The BAS email forum address is: firstname.lastname@example.org
Comet Holmes Photo by BAS Member Wyck Hoffler
2.8 Friends of BAS
Being a part of BAS also includes opportunities to participate in events with other astronomy and space
related organizations. This includes but is not limited to:
• Melbourne Astronomical Society (MAS)
• Central Florida Astronomical Society (CFAS)
• Kennedy Space Center Amateur Astronomers (KSCAA)
• And science professors and educators at local colleges and elementary schools.
2.9 BAS Club Loaner Telescopes
Our members enjoy access to two loaner telescopes shown in the photographs below. Along with being
able to personally use a telescope without owning one, an advantage of loaning telescopes to members is
that it may help them to determine which type of telescope they would most enjoy purchasing.
• an 8" Dobsonian Orion SkyQuest XT8 reflector,
• and a custom-built 16" Dobsonian reflector.
The loaner telescopes can be checked out by BAS members. Contact any BAS Officer listed in this
package or check on the BAS Website for current location of either telescope.
The “Procedure for Loan/Possession of Club Owned Telescopes” is located on the BAS Website, and is
briefly described here:
• The club telescopes are for the use and enjoyment of sanctioned club members. Any club
member can be asked to be added to the list authorizing them to use a telescope.
• The general expectation of the club when a member borrows telescope assets is to promote
general good keeping of the items and store in a protective environment.
• A borrower can checkout a telescope in person, by telephone, or email from any one of the club
officers. No written receipt is required.
• Telescopes are borrowed one month at a time, with extensions allowable each proceeding month.
Telescopes can be reserved for future loans also.
• Telescopes being returned to the club or transferred to another borrower are inspected, and then
given back to the club or next borrower.
• The club wants members to borrow these telescopes. All the club asks is that we take care of
8” Dobsonian Orion 16” Dobsonian Reflector
3 Star Parties and Outreach
What is a Star Party??? --- A gathering of Astronomers (Amateur, professionals, other star gazers,
families and friends) to share the night sky, share experiences and stellar sights. An opportunity to
compare telescopes, techniques, observing goals and to spark interest astronomy in others. It's a time to
share and teach each other about astronomy, to relax and enjoy beautiful wonders of the Universe. Good
clean fun for all ages.
At star parties we share knowledge and optical equipment with each other monthly or more often, under
moderately dark skies at moderately remote observing sites in the surrounding area. Visitors of all ages
are welcome! No equipment or experience is necessary -- only a keen interest in learning more about the
night sky. Please see our events calendar on the BAS Website for the next star party in your area.
3.1 Star Party Etiquette
When attending a Star Party, there are certain guidelines to follow that are courteous and considerate to
your fellow amateur astronomers. The guidelines are appropriate for safety reasons, and for the visual
enhancement of celestial observations with or without a telescope or binoculars.
There is a Star Party Etiquette article available on the BAS Website, therefore please read the article to
become familiar with Star Party Etiquette. A few key points from the article are:
• When approaching a Star Party site, please Drive Very Slowly, for the safety of all.
• Try to arrive early before dark. Turn off headlights, and use parking lights. Ask for assistance if
you don’t know where to park.
• Don’t use “White Light” such as bright flashlights. White light hinders your ability to see at
night, therefore use a “Red Light” to get around.
• Don’t litter.
• Even though not required, bring a telescope if you have one. Other amateur astronomers will be
happy to look through your telescope also.
• Don’t touch telescope or eyepiece optics with your fingers. Many telescopes and associated
equipment can be quite expensive, and oil/dirt from fingers can eventually damage protective
• Bring protective clothing depending on the weather and your comfort level.
• Bring Insect Repellant. Mosquitoes are bad in Florida and tend to visit our Star Parties also.
• Enjoy the Star Party and don’t be shy about asking questions, or sharing what you know.
3.2 Star Party Request
If you desire a Star Party or Solar Viewing, or someone else has contacted you for an event to be
conducted or attended by the BAS, please submit a “BAS Star Party Request Form” to the Outreach
Coordinator or any BAS Officer listed earlier. The form is located on the BAS Website and in the last
section of this packet.
Please provide the BAS with as much information as possible so we can support your Solar Viewing or
Start Party event.
3.3 Star Party Sites / BAS Points of Interest
The following sites are common locations where BAS participates in star parties and related events.
• Shilo, north of KSC A permit is required for using this area. A printed copy of the
permit is available from the outreach coordinator.
• Harmony, St, Cloud Unique town community that supports a dark sky lifestyle and
conducts a yearly Dark Sky Festival which BAS participates
• Camp Zyxlor, St. Cloud Home of a BAS member who graciously opens his dark sky
property location to conduct star party observing and/or
astrophotography sessions with fellow BAS members.
• Space View Park, Titusville BAS has provided Solar Parties at this location during NASA
space vehicle launches.
• Wickham Park, Melbourne Various community star parties have been held at this public
• Erna Nixon, Melbourne BAS supports start parties during the “Moonlight Stroll” event
conducted by the park.
• FIT, Melbourne Florida Institute of Technology occasionally conducts various
astronomy related events for which BAS supports.
• BCC Observatory & Planetarium Local community college with a computer-controlled 24”
Telescope in an observatory, and a 70 foot dome planetarium.
• F. Burton Smith Park, Cocoa BAS supports start parties during scouting events at this park.
• Space Coast Stadium, Viera BAS occasionally supports Solar Viewing & Star Party
observing at selected baseball games outside the stadium.
• Chiefland, FL Chiefland Astronomy Village. Astronomy club located west of
Gainsville. Some of us share membership with this club.
Part of the BAS objective is to foster interest and appreciation of astronomy with the general public
through lectures, seminars, study groups, public star observing sessions, exhibits, and any and all other
Our Outreach Coordinator is the clubs central point of contact for coordinating our various community
outreach events. Any BAS Officer may be contacted for requests. They will be happy to forward the
information to our Outreach Coordinator for scheduling.
If you or someone else has contacted you to request a Star Party or other related event, the BAS Outreach
Coordinator can be reached at the following email address:
Star Parties and Other Events
As evident in this package, there are many activities and events that occur throughout each year
supporting the community. If not for volunteers such as our BAS members, many of the events would
not successfully occur. There are many opportunities for volunteering and you are encouraged to do so,
no matter what your experience, and, no equipment is necessary if you so choose.
During each monthly meeting, past and upcoming Star Parties and related events are discussed, and
requests for volunteers are made.
Please feel free to contact any BAS Officer or the Outreach Coordinator to volunteer. Most all events are
brought up in the BAS email forum detailing specific locations, date and time.
Volunteering at BCC Observatory
Another opportunity for BAS Members is to support public observing sessions at the Brevard Community
College Observatory at the BCC Cocoa Campus. As described in the next section, the observatory is
open to the public for free on Friday and Saturday nights.
As a volunteer you will be trained to assist in the use of the large 24” computer controlled telescope. No
matter what your level of experience, the public appreciates the sharing of your knowledge about the
night sky with them.
Please contact any one of the BAS Officers, or the BCC Planetarium & Observatory Director at their
website listed in the next section, or use the following email address, if you desire more information and
would like to volunteer at the observatory:
Email forwarder for BCC Observatory Volunteering:
More information such as opening and closing procedures for the observatory, and volunteer scheduling
can be found on the BAS Events Calendar located on the bottom of the following webpage at:
Omega Centauri Globular Star Cluster Photo by BAS Member Wyck Hoffler
4 BCC Planetarium & Observatory
The BCC Planetarium and Observatory (BCC P&O) is located at the Cocoa, FL, BCC Campus described
earlier in Section 2.4.
BAS conducts our monthly meetings here, and both BAS and BCC P&O share an on-going mutually
beneficial, and friendly relationship when conducting various community events.
The BCC Observatory is home to the largest public telescope in Florida. The telescope is a Ritchey-
Chrétien design and is 24 inches in diameter. The observatory is open to the public on any Friday or
Saturday night, from sunset to 10:15 pm (closed on Christmas Eve, and on New Years Eve.)
24” Ritchey-Chrétien Telescope
The BCC Planetarium has seating for 210 under a 70-foot dome projection screen. Two star
projectors team up to produce a stunningly realistic sky and 3D computer effects.
There are many opportunities for exploration of astronomy and space related topics at the BCC P&O.
Please visit their website at the following internet address for a multitude of information and planetarium
The following is a reprint from the BCC website summarizing the facilities:
We've got a large-format movie theater that plays science films to the public and to school
groups. There are exhibit halls featuring hands-on science and historical artifacts from human
spaceflight. Our gift shop has plenty of items ranging in price from a few cents to a few dozen
dollars. Of course we've got the premier planetarium in East-Central Florida. And let us not
forget that we've got a rooftop observatory featuring a very large telescope which is free and
open to the public every weekend. A classroom seating 35 students and a portable "starlab"
planetarium round out the varied spaces in our building.
Planet Mars Photo by BAS Member Wyck Hoffler
5.1 Astrophotography in Brief
Astrophotographers use various techniques to capture and record celestial images called astrophotographs
using digital or conventional film. After looking at some examples of astrophotography you may agree
that it is also an art. There is so much information covering astrophotography available that we’re not
going to describe how to take photographs. Various techniques such as elaborate digital or film camera
mounted to telescopes with accurate tracking and exposures are available, at a cost. Or, you can pursue
simpler low cost techniques such as capturing star trails without a telescope, mounting a digital camera up
to a telescope to take planetary photos, or even using a webcam. There are many avenues possible based
on your ambition, budget, and types of photos you may desire to obtain.
Within our club there are many experienced amateur astronomers who have learned techniques to capture
celestial images that would rival photographs from years ago. These same BAS members would be
happy to share their wealth of knowledge with you, and it is quite common at monthly meetings to see a
review of recent astrophotographs taken by BAS members.
And again, there is a wealth of information on the internet about astrophotography, therefore near the end
of this package in the Useful Links section, there are several recommended websites for your reference.
But you’ll also want to consider doing a search for specific techniques yourself on the internet, or look in
the library or bookstore.
5.2 How to Submit Photo(s) to BAS Website
Aristoteles Crater by BAS Member John Small
If you are a BAS member and have photos that you would like posted on our website, please bring them
on a memory stick or CD-ROM to a BAS meeting (if the file sizes are large or there are many that you
would like to submit), or email them to the following email address:
Pictures of big events are appreciated but be aware that submitted photographs do not necessarily have to
be celestial images; they may be of people at any one of the events that you’ve attended.
Planet Jupiter Photo by BAS Member Bill Manley
6 Astronomy Beginner Books
Beginner’s Book List
Everyone needs certain printed items to get off square one in astronomy. Here are ideas of the most basic
low-cost beginner’s library. These are only a few of the many potential books to use. Your local library,
bookstore, or even books and material available via the internet are resources that can be used.
Naked-eye sky map: The one in the center of each issue of Sky & Telescope is excellent for the times
and dates printed in its upper-right corner. But you’ll also want a well-designed planisphere, a star wheel
that you can set to create a sky map for any time and date. The Night Sky by David Chandler is a fine
basic choice. Also get Chandler’s excellent companion pamphlet, Exploring the Night Sky With
Binoculars. Extra bells and whistles (including an altitude and azimuth grid) are built into the Precision
Planet and Star Locator planisphere by David Kennedal.
A basic astronomy guide: What’s a stellar magnitude? Right ascension and declination? Nightwatch
by Terence Dickinson is one of many simple, nicely illustrated books that explain the basics. A Field
Guide to the Stars and Planets goes into greater depth; it’s more of a textbook than a field guide.
A 6th-magnitude star atlas: This is your stepping stone to more involved naked-eye and binocular
study. The Bright Star At/as 2000.0 has excellent maps paired with tables of interesting objects, but not
much in the way of explanations. The costlier Norton’s 2000.0 has fine maps and an extensive, more
advanced rundown of observational astronomy.
When you get a telescope you’ll need a larger, more detailed atlas: the 8th-magnitude Sky Atlas 2000.0 by
Wil Tirion. For the companion reference this atlas requires, an excellent choice is the three-volume
Burnham’s Celestial Handbook.
Solar Eclipse 1991 Photo by BAS Member Wyck Hoffler
The following article about Astronomy was written by Alan MacRobert and is reprinted
with permission from Sky and Telescope, New Track Media, 2008.
7 Stargazing Basics: How to Start Right in Astronomy, by Alan MacRobert
Did you know you can see a galaxy 2½ million lightyears
away with your unaided eyes? Craters on the
Moon with binoculars? Countless wonders await you
any clear night. The first step is simply to look up and
ask, "What's that?" When you do, you're taking the first
step toward a lifetime of cosmic exploration and
But what, exactly, comes next? Too many newcomers
to astronomy get lost in dead ends and quit in
frustration. It shouldn't be that way.
What advice would help beginners the most? A while
ago, the Sky & Telescope editors got together to
brainstorm this question. Pooling thoughts from more
than 100 years of collective experience answering the
phones and mail, we came up with the following
pointers to help newcomers past the most common
pitfalls and onto the route to success
Under the stars. How good an astronomer you
become depends less on your gear than on
building your knowledge and skills.
Comet Hale-Bopp in twilight, spring 1997;
photo: Mark Schroeder
It takes some practice . . . but pretty quickly you'll be able to trace out star
patterns in the sky with the help of star charts.
Sky & Telescope / photo: Akira Fujii
1. Learn the sky with the unaided eye.
Astronomy is an outdoor nature hobby. Go out into the night and learn the starry names and patterns
overhead. Use the monthly naked-eye star charts in Sky & Telescope, the hobby's essential monthly
magazine. Or download our free Getting Started in Astronomy flyer (which only has bimonthly maps).
Even if you live in a densely populated, light-polluted area, there's more to see up there than you might
imagine. Even if you go no further, the ability to look up and say, "There's Polaris" or "That's Saturn"
will provide pleasure, and perhaps a sense of place in the cosmos, for the rest of your life.
2. Ransack your public library.
Astronomy is a learning hobby. Its joys come from
intellectual discovery and knowledge of the cryptic
night sky. But you have to make these discoveries, and
gain this knowledge, by yourself. In other words, you
need to become self-taught.
The public library is the beginner's most important
astronomical tool. Comb the astronomy shelf for books
about the basic knowledge you need to know, and for
guidebooks to what you can see out there in the wide
universe. Read about those stars and constellations
you're finding with the naked eye, and about how the
stars change through the night and the seasons. If your
library doesn't have enough, cruise your local
bookstores (not to mention our own online store). And
check the magazine racks for Sky & Telescope. It offers
a big, user-friendly sky map each month, observing tips
and projects for all skill levels, and reports on frontline
The Internet has put a gateway to the entire
astronomy world on everybody's desktop. But
what beginners really need is a coherent
starting place, and that usually means books.
Sky & Telescope / Craig Michael Utter
Of course the Web is a tremendous resource. But the Web is a hodgepodge. There are excellent beginner's
sites (hey, you found this one!), but what you really need right now is a coherent, well-organized
framework into which to put the knowledge that you will pick up as you go along. In other words, you
need books. Go to the library.
3. Thinking telescope? Start with binoculars.
Even lightweight binoculars will reveal
hundreds of cosmic wonders, from lunar craters
and double stars to galaxies millions of lightyears
SkyWatch / Chuck Baker
Binoculars make an ideal "first telescope" — for several
reasons. They show you a wide field of view, making it
easy to find your way around — whereas a higherpower
telescope magnifies only a tiny, hard-to-locate bit
of sky. Binoculars show a view that's right-side up and
straight in front of you, making it easy to see where
you're pointing. (An astronomical telescope's view, by
contrast, is often upside down, is sometimes mirrorimaged
as well, and is usually presented at right angles
to the direction you're aiming.) Binoculars are also
relatively cheap, widely available, and a breeze to carry
And their performance is surprisingly respectable. Ordinary 7- to 10-power binoculars improve on the
naked-eye view about as much as a good amateur telescope improves on the binoculars — for much less
than half the price.
For astronomy, the larger the front lenses the better. High optical quality is also important, more so than
for binoculars that are used on daytime scenes. Modern image-stabilized binoculars are a tremendous
boon for astronomy (though expensive). But any binoculars that are already knocking around the back of
your closet are enough to launch an amateur-astronomy career.
4. Dive into maps and guidebooks.
Once you have the binoculars, what do you do with them?
You can have fun looking at the Moon and sweeping the star
fields of the Milky Way, but that will wear thin pretty fast.
However, if you've learned the constellations and obtained
detailed sky maps, binoculars can keep you happily busy for
They'll reveal dozens of star clusters, galaxies, and nebulae.
They'll show the ever-changing positions of Jupiter's moons
and the crescent phases of Venus. You can identify dozens
of craters, plains, and mountains on the Moon. You can split
scores of interesting double stars and follow the fadings and
brightenings of numerous variable stars. If you know what
to look for.
A sailor of the seas needs top-notch charts, and so does a
sailor of the skies. Fine maps bring the fascination of
hunting out faint secrets in hidden sky realms. Many
guidebooks describe what's to be hunted and the nature of
the objects you find. Moreover, the skills you'll develop
using binoculars to locate these things are exactly the skills
you'll need to put a telescope to good use.
A neat star-chart trick is to make a wire
ring the size of your binocular's or
finderscope's field of view. Slide it from
point to point on the chart, and you'll see
the star patterns that will appear in your
view as you navigate the sky. Here we're
narrowing in on NGC 2392, the Eskimo
Nebula in Gemini (dark green symbol),
using Sky Atlas 2000.0. See our starhopping
article to learn more on navigating
the sky this way.
Sky & Telescope
Plan indoors what you'll do outdoors. Spread out your charts and guides on a big table, find things that
ought to be in range of your equipment, and figure out how you'll get there. Plan your expeditions before
heading out into the nightly wilderness.
5. Keep an astronomy diary.
This one is optional. But we notice that the people who get the most out of the hobby are often those who
keep an observing logbook of what they do and see. Keeping a record concentrates the mind — even if
it's just a jotting like "November 7th — out with the 10x50 binocs — clear windy night — NGC 457 in
Cassiopeia a faint glow next to two brighter stars." Get a spiral-bound notebook and keep it with the rest
of your observing gear. Being able to look back on your early experiences and sightings in years to come
gives deeper meaning to your activities now.
For some people, anyway. If this isn't your thing or becomes too much of a chore, never mind.
6. Seek out other amateurs.
For good company and free advice, attend a
club meeting or a star party like the annual
Table Mountain Star Party near Ellensburg,
Washington, shown here.
Self-education is fine as far as it goes, but there's
nothing like sharing an interest with others. Hundreds of
astronomy clubs exist worldwide; see our directory. Call
or e-mail a club near you, or check out its web site, and
see when it holds meetings or nighttime observing
sessions — "star parties." These events, some of which
draw hundreds of amateurs, can offer a fine opportunity
to try different telescopes, learn what they will and will
not do, pick up advice and new skills, and make friends.
Astronomy clubs range from tiny to huge, from moribund to vital, from ingrown to extremely welcoming
of newcomers. You'll have to check them out yourself. But none would be publicizing themselves in our
directory if they weren't hoping that you would call.
7. When it's time for a telescope, plunge in deep.
Eventually you'll know you're ready. You'll have spent hours
poring over the ads and reviews. You'll know the different kinds
of telescopes, what you can expect of them, and what you'll do
with the one you pick.
This is no time to skimp on quality; shun the flimsy, semi-toy
"department store" scopes that may have caught your eye. The
telescope you want has two essentials. The first is a solid, steady,
smoothly working mount. The second is high-quality, "diffractionlimited"
Naturally you'll also want large aperture (size), but don't lose sight
of portability and convenience. Remember, the best telescope for
you is the one you'll use most. Sometimes gung-ho novices forget
this and purchase a huge "white elephant" that is difficult to carry,
set up, and take down, so it rarely gets used. How good an
astronomer you become depends not on what your instrument is,
but on how much you use it. (For more specific tips on buying, see
"A Guide to Choosing a Telescope").
Big ones, little ones, fat ones, skinny
ones — whatever kind of telescope
you choose, don't skimp on quality.
A good one will serve you for a
Sky & Telescope / Craig Michael
Many new telescopes have built-in computers and motors that can, in theory, point the scope to any
celestial object at the push of a few buttons (after you do some initial setup and alignment). These "Go
To" scopes are fun to use and can certainly help you locate sights you might otherwise overlook. But
opinions in the amateur-astronomy world are divided about whether "flying on automatic pilot," at least
for beginners, keeps you from learning to fly on your own. We think it's important, at least for backup
purposes, to be able to use your charts and constellation knowledge to find telescopic objects by yourself
— especially if the scope's batteries die after you've driven 50 miles to a dark-sky location!
It's true that telescopes can cost thousands of dollars, but some good ones can be had for only a few
hundred. Can't afford the scope you want? Save up until you can. Another year of using binoculars while
building a telescope fund will be time you'll never regret.
If you choose to start with a small but high-quality scope, it can serve as your traveling companion for a
lifetime — whenever it's impractical to bring along the big, more expensive scope that you eventually buy
when your commitment to the hobby has passed the test of time.
8. Lose your ego.
Astronomy teaches patience and humility — and you had better be prepared to learn them. Not everything
will work the first time. You'll hunt for some wonder in the depths and miss it, and hunt again, and miss it
again. This is normal. But eventually, with increasing knowledge, you will succeed.
There's nothing you can do about the clouds that move in to block your view, the extreme distance and
faintness of the objects you're looking for, or the special event that you missed because you got all set up
one minute too late. The universe will not bend to your wishes; you must take it on its own terms.
Most objects that are within the reach of any telescope, no matter what its size, are barely within its reach.
So most of the time you'll be hunting for things that appear very dim or very small, or both. If flashy
visuals are what you're after, go watch TV.
9. Relax and have fun.
Part of losing your ego is not getting upset at your telescope because it's less than perfect. Perfection
doesn't exist, no matter what you paid. If you find yourself getting wound up over Pluto's invisibility or
the aberrations of your eyepiece, take a deep breath and remember why you're doing this. Amateur
astronomy should be calming and fun.
Learn to take pleasure in whatever your instrument can indeed show you. The more you look and
examine, the more you will see — and the more you'll become at home in the night sky. Set your own
pace, and delight in the beauty and mystery of our amazing universe.
Copyright © 2008 New Track Media. All rights reserved.
8 Telescope Basics
There are many resources to use when looking for information and advice concerning telescopes. The
internet has become a large electronic vault of information including astronomy and associated items like
telescopes and accessories. And libraries and bookstores still contain many written resources about
telescopes. If you aren’t familiar with telescopes, or would to refresh your knowledge about telescopes,
this section includes a presentation by BAS on Telescope Topics, and an excellent article about how to
choose a telescope. And don’t forget, there are many members in the BAS club who would be happy to
talk about the telescopes they have and recommendations.
DO NOT OBERVE THE SUN WITH A TELESCOPE UNLESS YOU HAVE THE
PROPER EQUIPMENT/FILTER AND YOU ARE COMPLETELY FAMILIAR
WITH THE SAFE USE OF IT.
Below is a reprint of a presentation given at a BAS meeting concerning telescope
definitions, types, and suggestions.
Aperture: Aperture refers to the size of the light gathering part of the telescope. Often measured in
Focal Length: The distance required for the light gathering part of the telescope to focus the light to a
single point. Often measured in millimeters. To convert inches to millimeters, multiply the inches by
Focal Ratio: The number calculated by dividing the focal length by the aperture, in the same units, of
course! Focal ratio is often written as f/5, which means a focal ratio of 5.
Newtonian Reflector: A telescope invented by Sir Isaac Newton that uses mirrors instead of lenses to
collect and focus light.
Refractor: A telescope that uses lenses to collect and focus light. Refractors are what most people think
of when they think of a telescope.
Schmidt-Cassegrain: A compound telescope that uses the refractive qualities of glass and a reflective
mirror to collect and focus light.
Eyepiece/Ocular: Device used to magnify the image formed by a telescope.
Magnification: Calculation of magnitude is accomplished by dividing the focal length of the scope by
the focal length of the eyepiece, i.e..., 1000mm ‘scope with a 25mm eyepiece results in magnification of
40 (1000/25 = 40).
Eye Relief: The distance the eye must be held from the rear of the eyepiece to form a good image.
Eyepiece design impacts eye relief, as does eyepiece focal length. In general, the longer the focal length
the better the eye relief. Also, some eyepieces are designed for eye relief, for those who wear glasses.
They normally sacrifice field of view. The TeleVue Panoptic series, their longer plossls, as well as the
Vixen Lanthanum series, and the Pentax XL series of eyepieces all offer good long eye relief that allow
many observers to use glasses.
Barlow: A device that is capable of increasing the effective magnification of an eyepiece. Most barlows
multiply the eyepiece magnification by 2 or 3 times. Barlows are effective at increasing the range of
magnifications available, but at an expense. Barlows often add small errors to the final image, but, if
designed well, they are often negligible. Many astronomers use barlow lenses since they allow higher
magnifications while maintaining the longer eye-relief of the lower power eyepiece.
Finder ‘scope: A small ‘scope attached to the main telescope that has a wider field of view than the main
instrument. It is used to find and center an object, or piece of sky where an object exists. Finder’s come
in two flavors: one-power finders, or magnifying finders. One-power finders are popular at real dark
sites, because they facilitate finding objects with crosshairs or a bulls-eye target projected against the
night sky, like a Heads-Up-Display. Magnifying finders are most useful if the aperture is wide enough:
50mm or larger. They are often sold or advertised as 5X20 or 7X50. Like binoculars, the first number is
the magnification and the second is the aperture in millimeters.
8.2 Telescope Types
As mentioned in the definitions, there are three basic types of telescopes used by amateurs and
professionals: the refractor, the reflector, and the compound telescope. All three have advantages and
disadvantages. Which is right for you? That answer depends on several things, but the most important
are observing interests, lifestyle, and the need for easy portability. Each of these must be considered
before making a choice. In the following paragraphs, the advantages and disadvantages of each, as well
as their fit to the above criteria are discussed.
Refractors are the visual representation of the classical telescope. The refractor was the first type
developed, and has had a steady following all these years.
1. Refractors are the most rugged of the three designs. In general, the tube is closed and the
objective is well protected. Refractors seldom need collimating.
2. Refractors offer the most efficient transfer and use of light. The transmission efficiency often
exceeds 93 percent on good designs.
3. Refractors offer the best performance, if well made, with respect to contrast and resolution in
the same aperture range.
1. Refractors are subject to an aberration (error) called chromatic aberration. This results in
false color and rings of violet light around bright objects like Venus or Sirius. Special
combinations of glass can compensate for chromatic aberration.
2. Refractor lenses are very difficult to manufacture. They require perfect glass and precise
3. Mounting large refractors is not a trivial problem.
4. The above make refractors the most expensive ‘scope for the aperture.
1. Refractors are used mostly to observe bright objects such as planets, the Moon, and brighter
deep sky objects. Recently, wide field or short focal length refractors have become popular.
They allow wide field views of deep sky objects and, with their good contrast, are very good
at viewing large bright nebulae (North America, Lagoon, Orion) and bright galaxies.
2. Many premium refractors are used by astrophotographers because of their superior light
transmission, quality of images, and contrast.
3. Double star and variable star observers also use premium refractors.
4. The smaller models of refractors are very portable. Besides their ruggedness, they are often
lighter than other scopes of similar aperture. In the larger models, the tube length becomes
such that they require larger mounts and are much less portable.
5. Refractors under 5 inches in aperture reach thermal equilibrium very quickly, and are very
good for quick or short observing sessions.
Reflectors are telescopes that use mirrors. The primary mirror is shaped such that the light striking it is
reflected to a focus point in front of it. Reflectors are popular because of their ease of construction, low
cost per inch of aperture, and ability to be mounted low to the ground.
1. Reflectors use mirrors to reflect light vs. refractors actually bending light. Because of this
they do not suffer from chromatic aberration.
2. Reflectors offer the most aperture per dollar of the three designs.
3. If well constructed and designed, contrast and resolution can approach that of refractors of the
4. Since you observe from near the top of the tube, the ‘scopes center of gravity will almost
always be low to the ground, offering the potential for extremely stable mounts.
1. While reflectors do not suffer from chromatic aberration, they do have the potential for
spherical aberration, caused by the primary mirror being slightly the wrong shape.
2. Most reflector designs use a small secondary mirror to divert the converging cone of light
from the primary to the side of the tube, where it can be viewed. This secondary will
adversely affect the resolution and contrast of the ‘scope.
3. Reflectors are open tube designs; the optics will eventually get dirty and require cleaning.
4. Reflectors require frequent mirror collimation to operate at peak performance.
5. Large reflectors with over 12 inches of aperture are very dependent on seeing conditions, and
require long cool down times to reach thermal equilibrium.
1. Reflectors are popular among amateurs because of the aperture and mount considerations.
Reflectors are good general purpose scopes and they can be specialized into planetary ‘scopes
by using high focal ratios, or wide field use by using lower focal ratios.
2. Reflectors can be constructed to be extremely portable. With a truss tube design, telescopes
with apertures of 16 inches or more can fit into a small car, such as an Escort wagon.
3. Because of collimation and cleaning requirements, reflectors are not carefree. If built well
and handled gently enough, the need for collimation can be reduced. Careful storage can
reduce the accumulation of dirt.
Compound telescopes such as the Schmidt-Cassegrain (SC), use both mirrors and a thin lens called a
corrector plate to achieve focus. They have become popular because of their ease of use and portability.
Since observing is done from the rear of the ‘scope, many find them easier to aim, and to use for
astrophotography. The folded optical path design results in a very short tube for its focal length.
1. The SC design allows for a very short tube that can be mounted on a simple mount, known as
2. The short tube makes them very portable for their aperture.
3. There are a wide variety of accessories available for SC’s.
4. Because of the short length, their balance is affected the least when using attachments for
5. They are very popular, and available in several different models, from basic tube to computer
guiding and tracking.
1. The SC is not the most inexpensive per inch of aperture.
2. SC’s are subject to both spherical and chromatic aberrations, but in most cases chromatic
aberration is negligible. Spherical error resulting from inaccurately figured optics can occur.
3. Quality control at the two major manufacturers of SC’s over the past few years has been
erratic. Lately, it has improved, but you still take somewhat of a chance with buying one of
these ‘scopes. A few companies will test the ‘scope before shipping it to you. This increases
the cost a little, but it’s a lot easier to let them deal with any problems.
4. SC’s are very susceptible to dew. In larger models they also require long cool down times.
5. SC’s will need collimation from time to time, but less often than reflectors.
6. SC’s use a larger secondary mirror than most reflectors. This adversely affects light
transmission, resolution, and contrast.
1. SC’s are good general ‘scopes. The fork mount/wedge combination is simple to use and easy
2. If your pocketbook can swing it, the computerized models will show you hundreds, if not
thousands, of objects, with no knowledge required beyond the names of a few bright stars.
3. Many CCD users and astrophotographers use the SC or another compound design, the
Maksutov, because of the ease of balance, good aperture, and available accessories.
4. SC’s are very portable compared to other equatorially mounted ‘scopes of the same aperture.
8.3 Telescope Suggestions
As you can see, the choice of a telescope is not straightforward. There is no best telescope for all
applications, but rather a need to weigh your needs against the pros and cons of the various designs. We
can offer a few suggestions.
First astronomical scope
If your interests are viewing the planets and the Moon, then we suggest an equatorially mounted small to
medium sized refractor. These telescopes are not inexpensive, but for this type of observing they are the
best. A good alternative is a longer focal ratio reflector (f/7 or up) 6 inches in diameter or larger. Of
course, the tube will become very large if you go above f/9.
General purpose observing
We would recommend a 6- or 8-inch reflector with the equatorial or altazimuth mount. The choice of
mount depends on how much high power observing you wish to do. If the tube for a reflector is too
much, then an 8-inch SC is a good alternative.
Deep sky observing
An 8- to 10-inch f/6 or f/5 Dobsonian mount (altazimuth) reflector. While these tubes are long, the
aperture is what you need. If the tube is too big, the same diameter SC is a good choice.
Finally, remember that any telescope can be made to do any type of observing. However, different
telescope types have different strong points. When picking one, try to line up your interests with its
strengths. Two excellent books with more information on telescope selection are Starware and The
Backyard Observers Guide.
The following article about choosing a telescope was written by Adrian R. Ashford and is
reprinted with permission from Sky and Telescope, New Track Media, 2008.
Note: Within this article are references to a magnification calculator and lunar gif movie
file showing turbulent viewing conditions, but they are only usable while viewing
this article on the S&T website.
8.4 Choosing Your Equipment: How to Choose a Telescope, by Adrian R. Ashford
S&T's Guide to Telescope-Buying
This is an exciting time to become an amateur
astronomer. Never have novice stargazers been
presented with such a vast array of telescopes and
accessories to pursue their hobby. Naturally, this brings
the burden of choice: the bewildering variety makes it
hard for an uninformed consumer to make the right
Big scopes, little scopes, fat scopes, skinny
scopes — which one is right for you? This
guide will help you tell. And whatever kind of
telescope you decide to buy, don't skimp on
quality. A good one will serve you for decades.
Sky & Telescope / Craig Michael Utter.
Whether you're seriously considering buying that first
telescope or just daydreaming about it, this guide will
help you narrow your options. First we'll explore the
types of telescopes available, and then we'll discuss their
key features — the size of the primary lens or mirror,
type of mount, portability, computerization, and
accessories. We'll also look at the tradeoffs, because
every instrument has its advantages and disadvantages.
Before you buy anything, you must determine what's important to you. What do you most want to look
at? How dark is your sky? How experienced an observer are you? How much to you want to spend? What
storage space do you have, and how much weight do you want to carry? Answer these key questions,
familiarize yourself with what's on the market, and you'll be well on your way to acquiring a scope that
will satisfy you for many years to come.
Before examining the different telescopes available, it's worth knowing the basics of how they work.
The most important aspect of any telescope is its aperture, the diameter of its main optical component,
which can be either a lens or a mirror. A scope's aperture determines both its light-gathering ability (how
bright the image appears) and its resolving power (how sharp the image appears).
What does this mean? The bigger the aperture the better. With a 6-inch telescope you can discern craters
on the Moon as small as about a mile across — half the size of those visible in a 3-inch scope (under the
same conditions using the same magnification). The same two instruments turned toward a faint galaxy
on a moonless night would tell an even more dramatic story. Because the surface area of a 6-inch mirror
is four times that of a 3-inch mirror, it collects four times as much light, meaning the galaxy would appear
four times brighter. (Astronomically speaking, that's 1.5 magnitudes brighter.)
Power Isn't Everything
It may surprise you, but a telescope's aperture is not what determines its magnification ("power"). When
seeing a telescope for the first time, a novice will usually ask, "How much does it magnify?" The answer
is, "Any amount you want." Any telescope can provide an almost infinite range of magnifications,
depending on the eyepiece you put into its eye end.
But don't get the idea that super-high powers will do you any good. Two main factors limit the power that
shows a decent view with a given instrument: aperture (again) and the atmospheric conditions.
Only so much detail exists in the image created by a telescope's main mirror or lens, so you must find the
optimum magnification to see this detail — without spreading out the target's precious light too much,
making a dim object too dim to see or turning a bright object into just a big blur.
This is why observers generally use low powers for looking at faint things like galaxies and nebulae, and
no more than medium-high powers for bright things like the Moon and planets. Just as enlarging a
photograph too much will simply show you the grain in the film or the pixels on the chip, so too will
excess magnification just make your target blurry.
How much power is too much? There's a simple rule to find the top useful magnification: 50 times your
telescope's aperture in inches, or twice its aperture in millimeters. And that's if the scope has perfect
optics and the night air happens to be unusually steady.
This means that a high-quality 4-inch (100-mm) scope should not be pushed beyond about 200x. To put
this in perspective, even a small instrument that has good optics will show you Saturn's rings or the
principal cloud belts on Jupiter, since these can be seen at a magnification of 75x. On the other hand, if
you see a small, 60-mm department-store telescope scope labeled as delivering "300 power!!!", you'll
know it's advertising hype and you should wisely look elsewhere.
Now you know the maximum practical power for any given instrument. But how do you get it? What do
those little numbers on the eyepieces tell you about the magnification they give?
Every scope has a focal length, which is effectively the distance from the primary lens or mirror to the
image it forms. (This is not always the same as the length of the tube, since, as we'll see later, some
telescopes optically "fold" the light path internally.) Focal length is the large number you'll often see
printed or engraved on the front or back of the scope, usually between about 400 and 3,000 millimeters
depending on the scope's aperture and type.
Eyepieces have focal lengths too — 25mm or 10mm, for example. Simply divide the focal length of the
scope by that of the eyepiece; that's the magnification. For instance a 1,000-mm focal length scope, used
with a 25-mm eyepiece, delivers 1,000 / 25 = 40 power (or 40x).
Here's a simple magnification calculator:
Telescope focal length = 0
Eyepiece focal length = 0
Magnification = 0
Why Does the Moon Look Fuzzy?
Even with the best telescope, you'll notice that you can discern
finer lunar or planetary detail on some nights than on others.
Sometimes the sharpness of the view even changes from one
second to the next. At high power, you'll see that planets and
stars shimmer and blur on most nights. The fault lies not with
the scope but with Earth's turbulent atmosphere, and
sometimes with very local conditions such as warm air rising
from a nearby asphalt driveway that soaked up solar heat all
day. Astronomers refer to turbulent nights as having bad
Even the best telescope will give fuzzy
views on nights of poor atmospheric
‘seeing’. This lunar image shows the
Altai Scarp mountain range leading to the
90-km-diameter crater Piccolomini (lower
right). It’s a frame in a short GIF movie
(102k) you can run by clicking the image,
showing how turbulent air ripples and
distorts the view, blurring fine detail.
Large apertures allow observers to pick out faint objects and
fine detail on the Moon and planets, but regardless of aperture,
the better the seeing, the more you can see. Since steady air is
so important, large telescopes — even those in the 10-inchplus
category — are often limited to 250x or 300x on all but
the very steadiest nights.
Any experienced observer will tell you that with practice, you'll see more detail in an image — not only
because your eye gets better trained, but because the longer you look, the better your chance of catching a
few moments of unusually steady atmospheric seeing.
Is Bigger Always Better?
So why go for a telescope larger than 10-inch aperture if the sky conditions will limit you? Large
apertures are most often chosen by observers who want to gather as much light as possible for viewing
dim things: galaxies, nebulae, and star clusters. These so-called "deep-sky" objects are generally viewed
at much lower powers than the Moon or planets, so the quality of the atmospheric seeing is less of an
issue. Also, larger aperture generally leads to shorter exposure times for those interested in
astrophotography, especially when combined with a short focal length.
But even if a large instrument is within your budget, there's the question of portability. A really large
amateur scope requires either a permanent observatory so you never have to move it, or willing buddies to
help you lift and assemble it for each observing session, then take it down afterward. Clearly, there's a
tradeoff between convenience and performance &$151; and everyone will have his or her own definition
of what is "portable." It's easy to succumb to "aperture fever," in which you're seized by a compulsion to
buy the largest telescope you can. The sad fact is that the leviathan is all too often consigned to the
basement or closet, being too heavy and unwieldy for regular use. Remember, the telescope that you use
most often is the one that will actually show you the most.
Pay close attention to the weight of the scope you're considering buying, usually listed in the small print.
Get a barbell or a log that weighs this much on your bathroom scale. Carry the log around with you. Carry
it back and forth from where you'll store the telescope to where you'll use it. Are there stairs along the
way? How often will you want to do this at the end of a long day?
Scopes of Every Size and Shape
Having gained an appreciation of a few important optical principles governing a telescope's performance,
and the tradeoff between performance and portability, we can now explore the different types of scopes
You'll be forgiven for thinking there's an infinite variety from the ads in the astronomical press. Yet for all
their varied shapes and sizes, telescopes can be divided into three classes: refractors, reflectors, and
A refractor is the stereotype of how a telescope is supposed
to look — a long, gleaming tube with a large lens in front
and an eyepiece at the back. The front lens (the objective)
focuses light to form an image in the back. The eyepiece is a
little magnifying glass with which you look at the image.
High-quality refractors are often sought out by lunar and
planetary observers who value their crisp, high-contrast
images that can take high magnification. In fact, when well
made a refractor can provide the finest images attainable
with a given aperture.
A cross-section of a modern short-tube
refracting telescope. Most refractors have
tube lengths between 8 and 12 times their
aperture, which can make them unwieldly.
However, lunar and planetary observers
favor the high-contrast images such
SkyWatch / Gregg Dinderman.
Another advantage of the refractor is that it's generally more
rugged than other types of scopes, because its lenses are less
likely to come out of alignment. For this reason refractors
are well suited to those who wish to have a "pick up and go"
instrument or who have no desire to tinker with the optics.
But these nice features come at a price. A really fine large objective lens is a work of art that requires
special glass and individual hand-crafting. For this reason, refractors are the most expensive instruments
of any given aperture. Also, in their commonly encountered forms, refractor tube lengths can be
unwieldy. A 4-inch refractor can be 4 feet or more long. And since the eyepiece is at the lower end of the
tube, a tall tripod is required if you expect to observe objects overhead. Such a tripod has to be very
solidly built to prevent wobbles at high powers, so it may be heavy or unwieldy, not to mention
expensive. For deep-sky observers a refractor may not have enough light grasp for viewing faint objects,
and the fields of view may be narrow. Modern optical design has led to shorter, more manageable
refractors, but at a correspondingly higher cost.
It's Done With Mirrors
The second type of telescope, the reflector, uses a
mirror to gather and focus light. Its most common form
is the Newtonian reflector (invented by Isaac Newton),
with a specially curved concave (dish-shaped) primary
mirror in the bottom end of the telescope. Near the top a
small, diagonal secondary mirror directs the light from
the primary to the side of the tube, where it's met by a
conveniently placed eyepiece.
A cross-section of a typical Newtonian, the most
common reflecting telescope. Dollar for dollar, a
reflector is the best-value scope you can buy.
Occasional cleaning and realignment of the
optics may lessen its appeal to some users.
SkyWatch / Gregg Dinderman.
If you want the most aperture for your money, the
reflector is the scope for you. When well made and
maintained, a reflector can provide sharp, contrasty
images of all manner of celestial objects at a small
fraction of the cost of an equal-aperture refractor.
The tube of a Newtonian is considerably more manageable, too. Its length is rarely more than eight times
the diameter of the primary mirror, and frequently less. This means an 8-inch Newtonian can be housed in
a tube hardly over 4 feet long, fitting in the back seat of a small car for transportation to dark, rural skies.
Combine this with the Newtonian's generally low center of gravity well below the eyepiece, and you end
up with an instrument on a compact, stable mounting that presents the eyepiece at a convenient height for
just about any sky orientation.
And there's another benefit. A reflector is, by and large, the only type of telescope that shows you a
"correct-reading" image rather than a mirror image. This is especially important when you're trying to
compare what you see in the eyepiece to what's on a star map.
For the best value of all, much consideration should
be given to a particular type of reflector known as the
Dobsonian. This is a Newtonian on a very simple,
very rugged mount. These extremely popular
instruments are available in apertures from 4 inches to
more than 30 inches and represent the ultimate in
observer convenience for casual viewing.
Like all reflectors (there are other types, but we'll skip
them because they're rarely encountered in amateur
hands), a Newtonian will require occasional
maintenance. Unlike a refractor's solidly mounted
lens, a reflector's mirrors can get out of alignment and
hence will need periodic collimation (adjustment) to
ensure peak performance, particularly if the telescope
is moved frequently. This is no big deal once you get
the hang of it, and the mirrors of the average
Newtonian may not require tweaking for months at a
time. But for those not mechanically inclined, having
to collimate a reflector even occasionally may be
A variant of the Newtonian telescope known as the
Dobsonian, shown here, has become extremely
popular thanks to its low cost, ease of use, and
SkyWatch / Craig Utter
The reflector's open tube means that dust and dirt are more likely to accumulate on the optical surfaces
even if you're careful to cover the tube in storage, and this will mean occasional cleaning. Also, the
aluminized surfaces of a reflector's mirrors may need to be sent off for recoating every 10 or 20 years —
more frequently if you live in a badly air-polluted urban area or by the sea.
The Best of Both Worlds
A cross-section of a Schmidt-
Cassegrain telescope. Roughly
midway in price between Newtonians
and refractors, catadioptrics are both
compact and easy to upgrade owing
to a wide range of accessories. Click
the image to see one popular variant,
SkyWatch / Gregg Dinderman.
Then there's the third category of instruments, the catadioptric or
compound telescope. These were invented in the 1930s out of a
desire to marry the best characteristics of refractors and reflectors:
they employ both lenses and mirrors to form an image. The
greatest appeal of these instruments is that, in their commonly
encountered forms (the Schmidt-Cassegrain and Maksutov-
Cassegrain), they are very compact. Their tubes are just two to
three times as long as wide, an arrangement allowed by "optical
folding" of the light. The smaller tube can use a lighter and thus
more manageable mounting. The upshot is that you can obtain a
large-aperture, long-focus telescope that's very transportable.
But here too there are caveats. Like the Newtonian, the Schmidt-
Cassegrain needs occasional optical collimation that lessens its
appeal to those disinclined to tinker. Their fields of view can be
rather narrow, too. In terms of cost, aperture for aperture, the
catadioptric lies midway between the reflector and the refractor.
Like a Newtonian, the popular forms of compound telescopes have
a secondary mirror in the light path of the instrument, and this
slightly degrades performance for critical lunar and planetary
observations. Even so, when well made, a Schmidt-Cassegrain or
Maksutov will deliver very fine images of a wide variety of
In common with refractors, the tubes of catadioptrics are sealed so that dirt and dust are largely excluded
— a big plus for an instrument that you're going to take out into the country. But if you live in an area
where dew occurs (which is almost everywhere), some sort of collar or extension to prevent misting of the
exposed corrector plate at the front of the tube is a must.
In practice, many people seeking a highly versatile, very portable (for the aperture) scope that can be used
for all sky subjects and for astrophotography will tend to opt for some form of compound instrument.
Scopes of this type also tend to be the most highly "technologized," with many options such as
computerized pointing and photographic adaptations. In short, they're excellent general-purpose scopes
that can use a wide variety of accessories.
The best telescope in the world is useless unless it's on
a solid, stable, smoothly-working mount, one that
permits it to be directed to the desired part of the sky
and to follow a celestial object smoothly and precisely
as the Earth turns beneath it.
The mount of a Dobsonian, as illustrated here, is a
prime example of an alt-azimuth, or 'alt-az' scope.
The tube moves up-and-down (in altitude) and
left-to-right (in azimuth). Other alt-az mounts may
have slow-motion controls to permit easy tracking
at high powers.
Sky & Telescope / Chuck Baker
In realistic terms, a "stable" mount is one that, when
you're using a moderate to high power, will not
vibrate for more than a second or so after you rap the
tube. In particular, the view can't wiggle so much
when you hold the focus knob that you can't see when
you've found the sharpest focus. And when you let go,
the aim must not jump to one side. This completely
eliminates the typical "department-store" semi-toy
telescope from consideration.
While there are variations on a theme, you'll encounter
two types of mount: altitude-azimuth (or "alt-az") and
An alt-az mount operates like a tripod's pan-and-tilt head, moving the scope up-down (in altitude) and
left-right (in azimuth). Equatorial mounts also possess two axes, but they're tilted so that one can be
aligned with the rotational axis of the Earth.
If you're intending to use a small telescope for casual sky viewing or daytime use (say, birdwatching),
you'll find the alt-az mount preferable. Well engineered mounts of this type will have finely threaded
slow-motion controls that enable the scope to be moved smoothly by tiny amounts, especially important
when you're using high powers. The value of such refinements will be all too apparent when you are
tracking a star or planet at high magnification.
The Dobsonian is a form of alt-az mount. Inexpensive materials such as particleboard and Teflon figure in
its construction, resulting in a low-cost, low-center-of-gravity mount that (ideally) glides smoothly about
both axes with fingertip control. A Newtonian reflector mounted in this fashion is not only extremely easy
to set up and intuitive to use, but very good value, too.
For a telescope intended for astronomy, and for which
photography is a future prospect, consideration should be given to
some form of equatorial mount that automatically counteracts
Earth's rotation. It's far easier to track a celestial object with a
scope mounted this way, since you need only concern yourself
with turning the scope about one axis — not two simultaneously,
as in the alt-az. When an equatorial mount is properly set up,
turning the slow-motion control of its polar axis is all that's
required to keep an object in view.
More sophisticated mounts, including modern high-tech alt-az
mounts, have built-in electric motor drives to do this, freeing you
to concentrate on observing.
So is one type of mount better than the other? Not really, since
each has its strengths. For the casual observer who wants a highly
portable scope that can be quickly set up in a variety of locations,
an alt-az is preferable — especially a Dobsonian. An equatorial,
while virtually mandatory for most forms of astrophotography
and critical observations of the Moon and planets at high power,
needs to have its polar axis aligned with the rotational axis of the
Earth. While polar alignment is not particularly difficult and
becomes routine with practice, it can take a little time at the start
of your observing session if you want to do it really precisely
(necessary for photography but not for just looking).
An equatorial mount makes the
tracking of celestial objects easier as
the Earth turns. Once correctly set up,
the scope need only be turned about
one axis to follow an object across the
sky — and a drive motor can do this
automatically. An equatorial is
mandatory for most astrophotography.
Sky & Telescope / Chuck Baker
"Go To" Scopes
Currently in vogue are the computer-controlled robo-scopes
appearing on the market in various guises. These have mounts that
are controlled either by a built-in computer or remotely by an
external PC. This allows you to direct the scope to any object in
the computer's database.
At first glance these "Go To" units would appear to be the answer
to a novice's dream, since they ostensibly take the hard work out
of finding elusive objects like faint galaxies, star clusters, and
asteroids. "Hey," you might think, "I don't have to learn the sky!"
A current trend is the robotic 'Go To'
telescope that has a built-in computer
and database to make finding objects
simple. . . in theory. The downside is
that most designs require you to
perform an alignment procedure each
time you use it, so you still need to
know your naked-eye stars!
Sky & Telescope / Craig Michael
But it's not quite like that.
There's no denying that when well engineered (read expensive),
these robotic scopes are great fun to use, as they almost magically
slew across the sky in search of whatever you've keyed in, zeroing
in on the target to be presented in the eyepiece. But this
technology is only beginning to mature to the point where these
scopes will automatically orient themselves when you take them
outside and switch them on. Almost all Go To systems will ask
you to enter the geographical location of your viewing site (or the
nearest city) and the date and time at the beginning of each
This lets the onboard computer calculate the positions of any celestial objects you may care to look at.
Often you'll also have to level the telescope's tube, point it north (or south in the Southern Hemisphere),
and then launch into an alignment procedure that uses two bright stars (which you must know by name) to
synchronize the telescope's coordinate system with that of the sky.
It's true that this setup routine is easily mastered with practice. But it does take time. And for someone
completely unfamiliar with the sky, the vast majority of the current batch of robotic scopes have the
potential to be very frustrating at first. Still, some help is on the way. The newest crop of Go To scopes
include their own Global Positioning System devices to at least tell you (and the telescope) exactly where
you are and what time it is, making setup a little easier.
Then there's the question of how accurately the mechanical parts actually point the telescope where the
electronics think it's pointing. At astronomical magnifications, there is no room here for even very tiny
errors — meaning any costcutting in the mechanical design and manufacturing. A cheaply made Go To
scope won't work, no matter how fancy the electronics are.
Here's one last thing to keep in mind: the money spent on a Go To scope's electronic mount could be
invested in a traditionally mounted scope of larger aperture.
When used at medium to high power, a telescope shows you
only a tiny little bit of sky. This make pointing at a target a
frustrating process unless the scope has a finder.
As the name suggests, a finder assists you in locating
celestial objects. All but the smallest scopes need one. Most
common is a miniature telescope attached by a bracket near
the eyepiece of the main scope. It has a low magnification
and hence a wide field of view, and is equipped with
crosshairs like a gunsight. Once you align it correctly with
the main scope, centering an object in the crosshairs gets it
into the main telescope's view.
You need a reasonably big, high-quality finderscope. Look
for one that has an aperture (front lens) larger than an inch
(25mm) and appears well-made. Dinky, nearly worthless
finders are all too common on cheap telescopes.
Some form of low-power, wide-field-ofview
finderscope needs to be mounted on
your main telescope, to help you point it
where you want. Look for optical finders
(top) that have front lenses (objectives)
larger than 1 inch (25 mm). Or, if you
prefer, opt for a reflex sight that projects a
red dot or bullseye onto the sky. A reflex
sight limits you to naked-eye targets with no
magnification, but you can still star-hop to
SkyWatch / Craig Michael Utter
A popular alternative is the reflex sight, which projects a
point or ring(s) of light on the background sky when you
look from behind. Many people prefer this intuitively simple
option, but you're limited to naked-eye objects because this
type of finder has no magnification and no more lightgathering
aperture than the pupil of your eyeball. You can,
however, still "star-hop" from naked-eye targets to deep-sky
objects using the main scope at its lowest power — if you
have sufficiently detailed sky maps.
Can I Photograph What I See?
Assuming you've bought a new scope, it's almost
inevitable that you'll wish to use it to capture the beauty of
a planetary image on film or to emulate the marvelous
gallery of deep-sky photographs that grace magazines
such as Sky & Telescope. In principle there's no reason
why you shouldn't be able to, given the necessary
equipment, inclination, and time. But it's wise to get used
to operating your new scope visually, and learning your
way around the sky, before embarking on the
Photography of the heavens can be incredibly rewarding,
but it's as much an art as a science. The learning curve can
be steep, the equipment can get expensive, and getting it
right can consume a lot of time. While any telescope will
permit you to shoot the Moon, for just about everything
else you'll need a scope on a very rigid, well-engineered,
and precisely driven mount.
Recording what you see, either on film or
digitally, can be a rewarding experience. A
quality telescope on a driven equatorial
mount, a guide scope, and a camera will get
you started in astrophotography. And these
days taking a photo is only half the fun.
Image-processing software lets you enhance
your picture to bring out things in it that may
otherwise escape the eye.
Courtesy Alan Dyer
Everything Has Its Price
While it may be tempting, resist the urge to buy the cheapest telescope available. Most of these are poor
quality optically, mechanically, or both, and will disappoint. If you've a budget of less than $200, consider
good binoculars instead.
That said, quality instruments can sometimes be obtained secondhand that an experienced member of
your local astronomy club may be willing to check out on your behalf. Or have you considered building
one yourself? If you're gifted with your hands and enjoy working in wood, it's possible to buy the optics
and make a top-quality Dobsonian reflector yourself. Again, members of your local club may help.
Even if you have lots of money to spend, don't buy the largest, most expensive telescope you can find just
yet. Start smaller and more manageable. If you're just learning to identify the constellations, many of the
advanced features of a really expensive instrument aren't likely to be any use to you. And remember not
to get something too heavy to set up, take down, and store.
And, remember you need more than glass and metal. Be sure to save some of your budget for additional
eyepieces to expand the scope's magnification range, a very detailed sky atlas (essential!) and good
guidebooks, and any number of other accessories — particularly if you have astrophotography in mind.
So, is there a perfect telescope out there waiting for you?
Actually, there is — it's the one you'll use most often!
An optically superb but massive refractor will be
effectively useless if you can't carry it outside, and the
largest Dobsonian will not show you the faintest galaxies if
the only place you can use it is a light-polluted parking lot
in a city.
Consider carefully what you feel to be your primary
observing interest, where you're likely to be able to
observe, and what is "portable." Weightlifting is good for
you, but not everyone enjoys it.
Whoever you are and wherever you live,
there's a telescope just right for you. One of
the rewards of amateur astronomy is sharing
the universe with others through your scope
— and you're never too young to start!
Sky & Telescope / Craig Michael Utter
Contact your local astronomy club, which may have
observing nights when you can try various scopes and chat
with their owners. Don't be shy. Your local club wouldn't
have put itself in our database unless they wanted you to
A telescope is a big investment for most people, and the universe is not going away. So take your time.
Use binoculars to get familiar with using star charts and guidebooks to ferret out faint, difficult wonders.
Doing this will develop exactly the knowledge and skills that you'll need to use a telescope well. When
you do buy, you'll then be more likely to make a decision you're really happy with, and you'll possess an
effective key to unlocking a lifetime of cosmic wonders.
It's a clear night — what are you waiting for?
Copyright © 2008 New Track Media. All rights reserved.
9 Useful Links
The following astronomy related links are accessible from the BAS Website and are reprinted here for
Astronomy in Brevard
BCC Planetarium and Observatory
KSC Amateur Astronomers
Melbourne Astronomical Society
FIT Astronomy & Astrophysics Public Lecture Series
KSC Launch Information
Kennedy Space Center
Central Florida Astronomical Society
Sky and Telescope
Free SkyCharts Planetarium Software
Free Celestia 3D Planetarium Software
Free Stellarium Planetarium Software
Night Sky Network
International Dark Sky Association
Jack StarGazer (Miami Planetarium)
Tonight's Sky (Online Presentations)
Andy's Shot Glass (Telescope Instruction)
Telrad Finder Maps
NGC/IC Object Catalogues
Used Observing Equipment
Cloudy Nights Classifieds
Solar Data Analysis Center
Astrophotography Forum on Cloudy Nights
Fine-Art Astrophotography by Warren Keller
Brian Lula Instrumentation and Imaging
Robert Gendler Astro Imaging
Richard Bennion’s Ewell Observatory
Johannes Schedler’s Panther Observatory (Austria)
Shevill Mathers’s Southern Cross Observatory
Christopher Go (Philippines) [Lunar & Planetary]
Damian Peach (UK)
Harald Paleske (Germany) [Solar]
Christian Buil (France) [Software]
This section contains forms used by BAS. Note that these are also available on the BAS Website:
BAS Club Membership Application
BAS Star Party Request Form
Application form for BAS Membership
Submittal form for requesting a Star Party
The Brevard Astronomical Society
Club Membership Application
Membership Form (Please print clearly)
Mailing Address: Street_________________________________________________________________________
City _____________________________ State ___________________ Zip _________________
Applicant’s Signature: ______________________________________________ Date: __________________
If applicant is less than 18 years old, parent or guardian’s signature: __________________________________
Membership Dues (circle one):
Regular Annual $25.00 per year, due in January
New Members (prorated dues schedule)
January through March $25.00
April through June $20.00
July through September $15.00
October through December $10.00
Life $500.00 (must be lumped sum)
Return form with dues to the club treasurer or mail to:
Brevard Astronomical Society
P.O. Box 1084
Cocoa, FL 32922
If paying by check, make payable to BAS.
BAS Star Party Request Form
Please provide the BAS with as much information as possible so we can support your Solar
Observing or Star Party event and at least 1 month lead time to allow us time to find Scope
volunteers to support your event.
Name of the event or Star Party:
Location of the event, name of School, Park, Library etc.:
(Complete address to include zip code)
Date of event or Star Party. (Day, Month and Year):
Requested Date: _________________________ Alternate Date: _________________________
Time of event or Star Party. When It Starts and Ends:
Set up time. 1 hour before event starts to set up telescopes and equipment:
Will electricity be available? Yes___ or No___
How many persons are planning on attending?
Age group. Elementary, Jr. High, High school:
Point of contact, Name of person requesting the event or Star Party:
Home or cell phone number of POC:
Please email this list to: email@example.com