The stunning Orion Nebula - The Royal Astronomical Society of ...

The Cambridge Double Star Atlas, by James Mullaney and
Wil Tirion, pages 154, 30 cm × 23 cm, Cambridge University
Press, 2009. Price $35 US, spiral bound (ISBN: 978-0-521-
49343-7).
The Cambridge Double Star Atlas
is a lush, beautiful, and very
nice book that is worth being
added to the list of observing
resources for regular doublestar
observers. It will provide
new ideas for observing targets,
and because of the high quality
of the charts, which include a
variety of other plotted objects,
can serve as a general-purpose
star atlas, not merely a supplementary
document.
The telescope I normally use has an excellent 8-inch refractor
as its finder scope, which is used for object identification
and centring. It provides an excellent instrument for general
stargazing and to try out the charts in The Cambridge Double
Star Atlas. The “showpieces” are indeed wonderful, and any
minor quibble with inclusion or exclusion is reflective of
individual tastes and preferences. The star charts are beautiful,
easy to read, and allow easy navigation for “star hopping.”
The biggest issue here is personal: when you turn to a page to
look at a specific system, those other green double-star names
seem to beckon (or taunt) the observer. I found that when
examining a pair, I would usually bounce around and make
incidental observations of many others.
The stellar duplicity rate, given as approximately 80 percent,
can be a contentious number. At the same astronomy meeting,
I have seen different posters claiming that all stars (within
uncertainties) are double and that no stars (within uncertainties)
are double. Charles Worley used to say that “three out of
every two stars are double,” which is accurate if you look at it
the right way. A useful relationship is to consider a sample of
N stars. The number of binaries is M (= N/2). The number of
tertiaries (triples) is L (= M/3). The number of quadruples =
L/4, etc. It is not a rule, but approximately right, especially for
the sample we know best: stars that are nearby.
The table of designations and WDS (Washington Double
Star) codes in the book appear to come from an antiquated
version of the WDS. It was certainly updated for our most
recent major release of the catalogue in 2006.5. One of the
more difficult issues in dealing with the WDS as a database
is the presence of duplicate discovery designations—in other
words, different systems assigned the same 3-character +
4-digit code. They generally fall into one of two categories:
systems given the same numbers but published in different
lists, and those given an additional designation appended to
the original one.
Examples of the first are the binaries first resolved by W.
Herschel and both F.G.W. Struve and O. Struve. Sir William
Herschel published seven lists (I to VI, plus “new,” or N),
with stars of each list starting at number 1. In addition to
their original discovery lists, each of the Struves published an
appendix. Such multiple lists were completely spelled out in
the Aitken Double Star Catalogue (e.g. H IV 48), but when
the Index Catalogue (IDS) was compiled at Lick Observatory,
all of the other double-star designators were dropped for lack
of space. As a result there were, for example, five components
with the designation H 48! The source Herschel list was
given in the notes file to the IDS. Also changed at that time
were Greek letters as designators, which did not work in the
electronic card catalogue format of the IDS.
In the second (and fortunately rare) case, systems found quite
near to known ones were given the same designation plus
trailing character(s), e.g. ES 1293a or BU 885½. Sometimes
both components were assigned the additional characters,
sometimes only one. Occasionally two pairs in an entirely
different section of the sky were given the same designation by
the author (probably by mistake).
Each case was handled in a different manner. For the William
Herschel discoveries, a list identifier is added to column
three of each designation. For example: H 19 (at 16 hours)
was originally H II 19 and is now known as H 2 19, H 7 (at
18 hours) was originally H V 7 and is now known as H 5 7,
and H 111 (at 06 hours) was originally H N 111 and is now
known as H N 111. In the case of the Otto Struve appendix,
an A is added following STT in the name. For Friedrich
Struve (STF), he provided two appendices: those from the
shorter list (Appendix II) are designated STFB. For example:
STF 11 (appendix I) is now STFA 11, STF 11 (Appendix II)
is now STFB 11, and STT 252 (Appendix) is now STTA252.
Stars of the second type are given the same 3-letter discovery
designation but a new number, starting with 9001, to indicate
that they originally had a different designation. For example:
BAL2356b is now BAL9001, and BU 885½ is now BU 9001.
The case of missing discovery numbers was changed in the
earlier edition, WDS 2001.0. The electronic version of the
WDS listed in the list of references provides corrections and
notes to many of them.
The idea of “training the eye” as described in the text
sounds quite interesting. As described, it would seem that
pre-knowledge of the marks, especially if repeated, could
influence the sketching. A more thorough description of how
to avoid biases would be handy. Another tool I have found
handy is an eye patch over the dark-adapted eye. With an
eye patch and a red head lamp, your appearance can be quite
comical, but if the goal is optimizing observing, that would
seem a small price to pay.
October / octobre 2011 JRASC | Promoting Astronomy in Canada
221