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The science behind the total lunar eclipse Sunday night

Published: May. 15, 2022 at 6:14 PM CDT
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BISMARCK, N.D. (KFYR) - Look up tonight! Something pretty cool will be happening in the night sky for the first time since January 2019: a total lunar eclipse!

Total lunar eclipse timing in North Dakota
Total lunar eclipse timing in North Dakota(KFYR)

A lunar eclipse is caused by the Earth blocking sunlight from reaching the moon and causing a shadow across the lunar surface. The Earth has to be perfectly positioned and aligned in between the sun and the moon for a total lunar eclipse to occur. The sun-blocking Earth casts two shadows that fall on the moon during a lunar eclipse: the umbra is a full, dark shadow, and the penumbra is a partial, outer shadow.

During a total lunar eclipse, the moon turns a rusty red color, earning the nickname “blood moon.” The red appearance is caused by sunlight interacting with Earth’s atmosphere.

When sunlight reaches the Earth, our atmosphere scatters and filters different wavelengths of light (due to the composition of our atmosphere). Remember that the white light from the sun is made up of a full spectrum of colors from red to violet. Shorter wavelengths, such as blue light, are scattered outward (which is the same reason why our sky appears blue during the day), while longer wavelengths, like red, pass through the atmosphere and are bent — or refracted — into Earth’s umbra. When the moon passes through Earth’s umbra during a total lunar eclipse (as shown below), the red light reflects off the lunar surface, giving the moon its blood-red appearance. This process of scattering different wavelengths of light in Earth’s atmosphere, called Rayleigh scattering, is essentially the same process that makes our sunsets red.

Science behind the total lunar eclipse
Science behind the total lunar eclipse(KFYR)

There’s no need for any special equipment for viewing the total lunar eclipse Sunday night, contrary to the special sunglasses that you need to view a solar eclipse — simply go outside, look up and enjoy. However, binoculars or a small telescope will bring out the details on the lunar surface.

The name of the full moon Sunday night is the “flower moon,” and some may call it a “blood flower moon” because of the red appearance during the full lunar eclipse. The name comes from the fact that flowers are usually blooming during this time of the year — “May flowers!”

Flower moon Sunday night
Flower moon Sunday night(KFYR)

Another thing to look out for Sunday night along with the total lunar eclipse: a great viewing opportunity of the International Space Station (ISS)! Look to the southwest at 10:28 p.m. CDT/9:28 MDT with a seven minute viewing window.

International Space Station viewing opportunity Sunday night
International Space Station viewing opportunity Sunday night(KFYR)

And sky conditions should cooperate for the eclipse viewing and to watch the ISS fly by. Below is the cloud cover forecast for around 11 p.m. CDT. The scattered cumulus clouds that we saw Sunday afternoon will dissipate once we lose the heating of the day. There might be a couple of upper-level cirrus clouds after sunset, but that should not prevent us from seeing the moon during the eclipse.

Cloud cover forecast at 11 p.m. CDT. The different colors are the different height clouds that...
Cloud cover forecast at 11 p.m. CDT. The different colors are the different height clouds that are forecasted.(SPC HREF)

A total lunar eclipse can be seen from any given location — on average — once every 2.5 years. The next one will actually be pretty soon: November 8, 2022!

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