Take a piece of space with you
I made this as a bonus present for a friend who bought galaxy shoes from me. I found the pendant at A.C. Moore and I thought I could make something galaxy themed with it. It's super easy and cheap. It turned out pretty cool, too.
Find pictures of galaxies or nebulae online. Load them into whatever program you like. I just put mine in Pages. Minimize them and make them smaller. They need to be seriously small. I went a little too big but one nebulae still looked good. Once you find the picture that looks best under the the heart, trace around the heart and cut it out. Glue the picture to the back of the heart using Elmer's clear glue. Let it dry (I didn't and should have).
Once the picture is affixed to the heart, put super glue (I used waterproof in case she showers with it or wears it in the bath. I have done these things) in the pendant backing. Press the glass heart into the pendant back until it is positioned properly. Wipe away excess glue immediately with a paper towel or cloth. Let dry and wear with whatever chain you like. I used the ball chain and make it kind of long. Have fun!