From Thinkgeek:

TWO DEATH STARS? Well, yeah, okay, so there were two Death Stars. Just not both fully-operational at the same time. In this image the front Death Star has all the callouts and the rear Death Star has all the awesome. What do we mean? Turn the lights off. We thought for sure the green bit was going to be the glow-in-the-dark part of the design, but no. It’s that rear Death Star. *cues Imperial March*

Two Death Stars on a black 100% cotton shirt. Rear Death Star glows in the dark.

[Death Star Schematics Glow T-Shirt]