A reference pic of Eclipse Gazer (or Eclipsegazer), brand new and re-done! :3

Including a new version of her cutie mark.

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TL;DR: Cutie Mark meaning
Her cutie mark represents the moment of the eclipse, which is the darkness for many. But for her (and me), it means a moment when everything it's showing a new face, under two lights, and she considers this the moment of fair judgement. Nothing is black or white, but grey for Eclipse.

The three stars represent Eclipse's Precepts. All her family has three stars that symbolize their own Three Precepts. In Eclipse's case, they mean "Understanding - Decomposition - Re-composition", like in Alchemy, since she wants to understand everything.

So, long story short, her cutie mark represents the concept of Science, Alchemy and Magic. She wants to understand it, and for that she has to first decompose it, to later recompose it. For that, she tries her best to have a "gray" look over things, so she can be fair and learn more.