TriAtlas is a set of star charts published as free, downloadable .pdf files by a Spanish astronomer. In spite of its limitations, it is a wonderful product, going much deeper, fainter, and at a much larger scale than would be practical, or even possible, with printed star charts. I heartily recommend it. Learn how to acquire this product, and some of its technical properties and details here:
http://www.uv.es/jrtorres/triatlas.html
Mr Torres also provides a downloadable planetarium program called CNebulaX (also free!). I’m not familiar with it, but it certainly looks impressive. CNebulaX was used to generate the TriAtlas map sheets.
http://www.uv.es/jrtorres/CNebulaX.htm
Triatlas consists of three separate star atlases, A, B, and C. each progressively more detailed, deeper, and at a larger scale. As pdf files, each 8 1/2 by 11″ sheet can be brought up as a screen, or printed out separately to be taken to the telescope. The A atlas covers the whole sky to magnitude 9.5 in 25 sheets. It can also be downloaded in A3 format.
The C atlas goes down to mag 12.5 and 571 sheets (corresponding to a scale of about a degree per inch. It contains more stars and deep sky objects than anything in print, but is too cumbersome to print out, much less use at the telescope. It is also a bit cluttered and hard to read for field work, but as a desk reference it is unequalled. Nothing else even comes close, it must be seen to be believed.
The B atlas is an intermediate product that bridges the gap between the two (107 sheets).
The advantage is that the A and B atlases have the C sheet numbers printed on the mapping itself allowing each atlas to be used as an index map and navigational aid for the next atlas up.
I’ve downloaded the whole shooting match, and set up the series in a file structure that allows me to find my way around very quickly. I’ve printed out the A maps as a folder of 25 maps. When I find an object or area of interest, I bring up the B or C chart pdf covering that part of the sky in detail.
So far, I have only one criticism of this product, and I recommend it for all astronomers (you certainly can’t beat the price!). The Deep Sky Objects in the C charts are well labeled, but not all the abbreviations and acronyms are familiar to me. I know most of the major ones, like the New General (NGC) or Index (IC) catalogues, Mel for Melotte, Tr for Trumpler, etc, but many of the more obscure ones are unknown to me. There is no complete map legend or bibliography, and some of the catalogue labels are not found in the authoritative Wikipedia List of Astronomical Catalogues. So if I try to look up an obscure cluster or nebula I don’t know how to enter it into a search engine.
Other than that minor quibble, I highly recommend Triatlas. Its dwfinitely worth going to the man’s website and checking it out.