A solar eclipse happens when the moon the moon completely blocks the sun casting a shadow. The shadow is created when a new moon is present because the part of the moon that is facing the sun is lit and the other side isn't. So, the moon reflects with a shadow. The umbra is the darkest part of that shadow and is where you can see the total eclipse. Even if you are not in the umbra, you can still see a partial eclipse if you are standing in the penumbra. The penumbra is the lighter part of the shadow.