Star maps from the Terran perspective

I’ve previously done some posts on star maps that use the stars’ X, Y and Z coordinates to show where they are relative to each other (the first one is here and the rest were on succeeding days).  With this kind of map, you’re looking at your assortment of stars from a position in space that is light years away -- usually, farther to the galactic north.  This kind of star map is useful if you’re doing a story where the stars are not all visible from Earth at the same time and place -- for example, a story set in the first centuries of interstellar exploration, such as Larry Niven‘s “Known Space” series or Gordon Dickson’s “Childe Cycle”.

On the other hand, suppose your story takes place in an interstellar empire like the one we created over the last couple of days.  That is, it’s set among a number of stars that, as seen from Earth, are all located within one or two constellations.  An Earthbound observer could then point a telescope at the right patch of the night sky and locate all the stars in question.

If that’s the case, then you might be better off doing a map based on right ascension and declination.  This is the kind of map you will find in any star atlas or online astronomy guide, so it’s easy to consult one and visualize what your end result should look like.

You will recall that we created our empire using the HabHyg database.  Unfortunately, HabHyg doesn’t include the RA and declination of the stars it lists.  However, there are plenty of other resources that do include this information.  One is the HYG database, which HabHyg uses as one of its sources.  Several versions of it are located at http://astronexus.com/node/34.  As with HabHyg, I suggest you download a copy for your own personal use.

From that valuable resource, here are the coordinates for the stars in the empire, rounded down to the nearest tenth of an hour or degree:

NN 4178: 21.1, -50.4

GJ 2151/Woolley 9716: 21.1, -57.0

Woolley 9724: 21.2, -43.6

NN 4198: 21.5, -40.7

HD 205390/Gliese 833: 21.6, -50.8

Gliese 838: 21.8, -47.3

NN 4224: 21.8, -41.6

Gliese 838.6: 21.9, -47.0

Gliese 841 A: 22.0, -51.0

Gliese 841 B: 21.9, -51.0

HD 211415/Gl 853 A and B: 22.3, -53.6

HD 211970/GJ 1267: 22.4, -54.6

Now to make the map.  At this point, I suggest you get a copy of a star atlas and make a scan or photocopy of the page that has this particular part of the sky on it.  Alternatively, you could find one online and print it out. (If you’re like me, you may want to make several copies in case you make a mistake... or use a pencil for what follows.)

Next, put each star on the copied map by drawing a dot at the proper intersection of RA and declination.  The atlas will probably break down RA and declination into minutes rather than tenths of an hour or degree, but converting should not be much of a strain.  21.5 hours, for example, would be the same as 21 hours and 30 minutes.  As you put down each dot, label it with the star’s catalogue number, or with whatever made-up name you choose to give it, or both, and with its distance from Sol, to give your reader an idea of how “deep” the map is.

What I find neat about a map like this is that it gives the Earthbound reader a sense of how the imaginary empire ties in with reality... and how small a part of the sky even something so unimaginably huge would actually take up.