What Will You See?
A Lunar Eclipse is when observers on Earth see a full moon eclipsed by the Earth's shadow. The lunar eclipse will already be occurring when the moon rises at 5:45 PM. The sun will set at 6:45, and when it does so, you will see that the moon is glowing a deep red color; this phenomenon is explained below. As time passes, we will see the Moon slowly creep out of the Earth's shadow, and become much brighter. After that is done, it will in fact creep out of a second shadow, this also is illustrated below.
This is a simulation of what the Lunar Eclipse will
look like.
This is a 3 hour simulation condensed into a 10 second
video!
What's Going On Here?
As we learned in the last paragraph, the eclipse will already be happening when the moon rises. All that means is that the Moon already passed into the shadow of the Earth before it rose over our horizon. People who live in other parts of the world (East of Massachusetts - i.e. England) where night starts before it does in Amherst, MA would have seen the eclipse start.
Why does this happen?
To understand this phenomena, we first remember that the moon orbits around the Earth. It turns out that the Moon is tilted in its orbit, so occasionally (not every time) the moon will be directly lined up with the Earth and Sun, and it will pass behind a shadow of the Earth.
This is an illustration of what the Earth Moon Orbit looks like.
Remember this is NOT to Scale!
If the orbit of the moon around the sun were NOT inclined, if would look like this:
Remember: This is NOT the way the Earth-Moon system behaves
So it turns out that total lunar eclipses are rare occasions, but there is still a little more behind the total lunar eclipse that just the inclination of the moon to the earth.
There are two parts to a total lunar eclipse, penumba and umbra.
The penumbra is a partial shadow. This is the result of the sun light only being partially blocked.
Whereas the umbra is a total shadow, and no light is allowed to reach behind the Earth.
Here's another way to look at it:
Why is the moon red? I thought it was supposed to be in a total shadow?
During the middle of an eclipse, the moon appears to be a deep red. This is NOT an illusion. To understand what is happening here, lets think about what happens to white light when it passes through a prism. We have all seen demos where when white light is passed through a prism, it is broken down to its components.
The Earth has an atmosphere, which acts as a prism to the light coming from the Sun. When the light hits the top of Earths atmosphere, it breaks into components and bends around the Earth.
So because the atmosphere acts like a prism, it can bend light through it, and shine it where there is a total shadow.
However, notice that there is no blue light being bent through the atmosphere towards the moon? This is for the same reason the sky is blue - molecules of nitrogen in the Earth's atmosphere scatter blue light. Scattering blue light is just a scientific way of saying, "the atmosphere doesn't allow blue light to pass through it easily and sends it off in all different directions, which prevents it from passing cleanly through the atmosphere like the other colors can."