Eclipses and the path of light: Geometric optics
How do we get a solar eclipse?
Details about this, and the Earth-moon system in general, are here: Kaiserscience Earth-moon system.
But here are the basics:
How do we get a lunar eclipse?
First we need to know about the three types of shadows.
umbra (Latin “shadow”) is the innermost, darkest part of a shadow.
Where the light source is completely blocked.
penumbra (Latin paene “nearly”) is where only a portion of the light is obscured.
An observer in the penumbra experiences a partial eclipse.
antumbra (Latin ante, “before”) is where the occluding body appears entirely contained within the disc of the light source.
An observer here sees an annular eclipse, in which a bright ring is visible around the eclipsing body.
Here we see rays of light from the Sun, hitting the Earth. This happens 24-7.
Behind the Earth the three types of shadows always exist, 24-7.
If the moon passes through one of these regions, then we get one of these types of eclipses.
What are the conditions for a lunar eclipse?