All the Earths sunsets at Once: Prof. Kristen Thompson on Rare Lunar Trifecta
January 30, 2018
Sunset brought a very rare lunar confluence: a supermoon, blue moon and blood moon all on the same night.
We talked with Assistant Professor of Physics Kristen Thompson to understand the ultra-rare celestial shindig. Thompson is 91әs astrophysicist and has conducted research across the country. In August of last year, she led the 91 expedition to Winnsboro, South Carolina, for the Great American Eclipse.
Lets start with some basic definitions, in descending order of perceived menace. What is a blood moon?
The term blood moon refers to the reddish color the moon takes on during a lunar eclipse when Earth moves between the sun and the moon.
What produces that red color?
Its related to the same atmospheric effect that makes sunsets look so colorful. The atmosphere is very good at scattering blue light from the sun thats why the sky is blue.
When the sun is low in the sky, the light is passing through the most atmosphere possible, which can give the sky a reddish color. When the moon turns red, its because the light from the Sun is passing through Earths atmosphere, which is refracted as red light on to the moon. When you get to see a red moon, its like seeing all the earths sunsets at once.
Will we be able to see the blood moon on campus?
Unfortunately, the eclipse is happening right before sunrise, meaning the Moon will be extremely low in the western sky. To see even a partial eclipse, you will need a clear view of the horizon, which is not easy to get where we are.
Now, if you live farther west in the United States, you stand a much better chance of seeing the blood moon as long as youre willing to get up in the middle of the night.
But everyone will be able to see the supermoon, right?
Yes. Supermoon means that the moon is full when it is at perigee or closest to Earth. A supermoon can look up to 14 percent larger and 30 percent brighter although brightness can be hard to detect.
One interesting note about the moon is that it will look largest near the horizon, but it is actually the same size throughout the night. The horizon effect is purely psychological; a function of the brain using items on the horizon to exaggerate the sense of scale.
How rare is the supermoon?
Not terribly rare; it occurs approximately once every 14 months. Whats special about this one is its combination with the lunar eclipse.
And last: tonight also marks a blue moon which actually has nothing to do with color.
Thats right. A blue moon simply means a second full moon in a calendar month. A blue moon is actually more rare than a supermoon; the last one was in 2015. Even more surprising, we will have a second blue moon in March.
Jay Pfeifer
japfeifer@davidson.edu
704-894-2920
