Astronomy 115 - SFSU Physics & Astronomy

Astronomy 115
Instructor: Dr. Chris McCarthy
Sorry! This class is full. If you are not already
on the waitlist, you will not be admitted :(
However there might be room in:
Sec. 5: W 7:05 PM

Handouts Today:
Astronomy 115
-Course Syllabus
-Homework & Exam Schedule + AstroLingo
-Homework #1
Also: Please mark your name on roster.
Office Hours: Wed. 3:00 PM
Tuesday 2:00-3:00 PM
Office: TH 520

Textbook
Commins, “Discovering the Universe: From Stars to
Planets” (1st edition)
• Chapter 1: Night Sky
Reading
• (Optional: Sec. 1:6,1:7,1:8)

What is Astronomy?
Astronomy is the study of Everything, the entire
universe, and everything in it.

What is Astronomy?
Astronomy is a science.
It is based on the scientific method involving hypotheses,
experiments & theories
Understanding the world around us depends on our
ability to use critical thinking to distinguish valid ideas.
Ideas are not considered valid unless confirmed by
different groups of researchers.
To challenge or confirm a hypothesis, astronomers use
observations, made by eye or with a telescope.

Don’t Call it “Astrology”!
• Astronomy & Astrology were once one field,
trying to explain the heavenly motions.
• Today, astrology seeks to predict people’s fates,
based on “cosmic influences”
• Astrology can’t be verified

What is Astronomy?
• Astronomy is Thinking Big.
• Astronomers deal with quantities of time and space
much larger than normal experience.
• 1,000,000 years (1 million years) is less than 0.1%
of the age of a typical star.
• Our Galaxy alone has over 100 billion
(100,000,000,000) stars.
• The energy released by the Sun in one second is:
• 380,000,000,000,000,000,000,000,000 Joules
• (This is 10 trillion times the energy used by all
humans on Earth)

Dealing with large numbers
1. Give them Names
• 1,000 = thousand (kilo-)
• 1,000,000 = million (mega-)
• 1,000,000,000 = billion (giga-)
10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,00
0,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,
000,000 = 1 “googol”

Dealing with Large Numbers
• 1,000 = 10 3
• 1,000,000 = 10 6
• 1,000,000,000 = 10 9
2. Use Scientific Notation
• This makes calculations easier:
1,000 x 1,000,000,000 = 1,000,000,000,000
• Multiplying, add the exponents.
10 3 x 10 9 =10 12
• Dividing, subtract the exponents.
10 12 / 10 3 =10 9

• With Scientific notation, even googol seems
reasonable:
1 googol =
10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,
000,000
= 10 100
• READ Appendix A of your book to review
scientific notation.

A Quick Tour of the Entire Universe
You are here

South West San Francisco

Wait. Stop.
...be sure to mark your name
on the sheet!
Ok. Keep going

Moon’s Orbit around Earth
Earth
1,000,000,000 meters

Sun

The Sun and All Planets in our Solar System
15

The Nearest Stars

Sun
Our Home Galaxy, the “Milky Way” looks like this
Our Sun is one of over 100 billion stars here.

Milky Way and nearby, smaller galaxies

Thousands of these galaxies are grouped together into Clusters

The study of the entire universe is called Cosmology.
It raises many interesting questions.
Where did it all come from? Or has it always been here?
What will ultimately happen to the universe?
Could it collapse?
Will it blow itself apart?
Are we alone in the universe?
Or is someone else out there waiting to contact us?
???