It is thousands of years old and was made by the elf Datharian Mistwatcher when his home city was destroyed by the drow. After Datharian was slain in battle, the sword came to a female elf known only as the Stargazer, and she slew hundreds of drow with it. When she realized her sister had been killed in the Battle of Nine Arrows, she died of grief, whereupon another elf picked up the sword. It has been in the possession of many different elves since then.
The sword harms evil creatures who touch it and it is rumored if the longsword is held by a good drow, it will shatter into a thousand shards of moonstone, each worth around 50 gp, and would cast atonement on the drow. The blade is worth around 100,315 gp.