[Chaos-l] Wil Tirion's _The Cambridge Star Atlas_

[Jon Stewart-Taylor]

Hi all.  During my observing session last night at Farrington Point, i  
was using a copy of Wil Tirion's _The Cambridge Star Atlas_ (which i'd  
checked out of the library) to hunt things down.  I currently use  
Tirion's _Bright Star Atlas 2000_ as my main atlas, and was curious  
how the two compare, especially since _BSA_ was out of print for some  
years.  The first obvious difference is that _TCSA_ has a  moon map,  
listing about 250 craters as well as the various mares.  The map is  
inverted as per Newtonian 'scopes, but at a scale perhaps more suited  
to binoculars.  The monthly whole-sky maps are divided per-hemisphere  
in _TCSA_, as opposed to the one-chart-fits all approach in the _BSA_,  
and are are a pretty blue with the Milky Way in a lighter blue.  More  
importantly, there are 12 in _TCSA_, intended for use from 9 to  
midnight, compared to 7 in _BSA_ labeled with  the 16 month//time  
combinations each of the 7 charts cover.

The most important differences between _BSA_ and _TCSA_ are limiting  
magnitude and scale.  _BSA_ is a  mag 6 atlas, and covers the sky in  
10 full-page charts. _TCSA_ is a mag 6.5 atlas, and covers the sky in  
20 full-page charts.  _TCSA_ also lists fainter objects, some as faint  
as 12th mag, in contrast to the usual mid 10th magnitude limit for  
BSA. These differences mean that BSA is a better unaided-eye,  
binocular, and Telrad reference, while _TCSA_ is a better finder-scope  
and telescope reference.  Using _TCSA_, i sometimes had to flip back  
and forth between pages to get the layout of the bright stars used for  
Telrad hopping.  Conversely, the extra half magnitude, and especially  
the finer detail, helped in using the finder to close in on the targets.

The _BSA_ has a set of tables at the front, one listing all the  
Messier objects and one each for the double stars, clusters, galaxies,  
and nebula shown in the whole atlas.  Both atlases (atlasi?) have  
tables for each chart listing the objects on that particular chart.   
_TCSA_ has 4 charts at the end showing the distribution of each kind  
of object over the whole sky: kinda fun, but not something you'd refer  
back to all that often.

Bottom line is that you probably don't need both of these.  If you  
want to do primarily unaided eye or binocular observing, _BSA_ is  
probably better, especially given you can usually get it for under $12  
including shipping.  For telescopic purposes, _TCSA_ has better  
charts.  It also costs about twice as much, on the order of $24 in  
hardback.  Either is a good choice to pair up with _Turn Left at Orion_.

Hope this was useful.

J.
-- 
Jon Stewart-Taylor:  joncst at earthlink.net
Chapel Hill Astronomy: http://www.rtpnet.org/chaos