Mythology and Astronomy.
Star Table -- table of brightness/size of the stars in the constellation. I suggest using a star map with the greek letters to help.
Detailed star maps.
The idea I was trying to tattoo was the actual constellation of Scorpius, with stars in approximate position and size. On second thought, I decided I might want some shape behind the stars, so as not to be so bland. You may think it's heresy, but I didn't want an enormous scorpion... kind of cliche, if nothing else. So I looked into other mythologies to see what I could come up with.
Mythology surrounding Antares, the brightest star in Scorpius (and called the 'heart' of the Scorpion), led to the Chinese constellation of the Jade/Azure/Blue Dragon of the East. Wikipedia's article. We're the constellations Xin and Wei. More on Chinese Astrology.
Antares was also associated with the Egyptian goddess Selkhet.
More on Antares.
"The Witness of the Stars".
In the end, I decided to go back to just the constellation and working in some other ideas. However, I also decided to join the Navy, whom won't allow me to get any new tattoos until I'm done with basic training... some 10 months from now. :(