At the bottom of the workspace select "Create Frame Animation." (The triangle button beside this option will let you toggle between Frame timeline and Video timeline.)
On the timeline, click on the "duplicate frame" icon. With the next frame selected, make a new layer and click on it. With a soft round brush set at 30% opacity, paint a glow around the edge of the star.
Duplicate the previous frame, make a new layer and expand the glow.
Repeat step 5 a few more times, gradually increasing the size and amount of glow on each layer.
Check each frame in order, and activate only those layers you want to appear on each frame.
Change the repeat to "forever," and play your animation.
Adjust timing as needed:
Change timing of each frame.
Add in-between frames.
Reverse the action
Shift-select all the frames EXCEPT your first and last frames, and click the duplicate frames button.
Move those frames to the end of your timeline.
Rearrange them, or turn layers on/off to reverse glow action.
Play your animation. The action should loop smoothly.
File > Save for Web (newer versions of CC use File > Export > Save for Web).
Select GIF 128 No Dither.
Make sure Looping Options are set to Forever.
Can't change a rubric once you've started using it.