Why Does This Image Mean The Apocalypse?

Here's a science riddle or should I say an emoji symbol with science annotations because it's a riddle showing the Earth and the Moon plus the Sun but in a sequence that for the third riddle it means it's the apocalypse but why?
If you can guess why this image means it's the apocalypse then good on you. But why does it mean it's definitely the apocalypse? I got it pretty much straight away, well within 10 seconds when you think about time and the relativity blah blah.

If you guess it right you win a biscuit, go get one. If you guess incorrect wait til mom gets home your dead! Answers on a postcard.

Hovering over the image looking for the answer is cheating by the way.

Original post can be found here.
The answer is, it would be real bad if the sun got between the Earth and the Moon. They call that "the apocalypse".