This Week: a Total Eclipse of the Moon

Last August 21, millions of people traveled to view a total eclipse of the Sun.  This Wednesday, January 31, 2018, there will be a total eclipse of the Moon.  While the total solar eclipse was visible only inside a narrow band of land, the total lunar eclipse will be visible to everyone on an entire side of planet Earth!

Here’s the short explanation of a lunar eclipse: On some orbits, the Moon travels through the shadow cast by the Earth.  If the Moon is above our horizon, we can watch our shadow darken the surface of the Moon.  If the Moon is completely darkened by the shadow, this is a total eclipse of the Moon.  Otherwise, it is a partial eclipse of the Moon.

Here are some links to detailed explanations, and information about viewing this eclipse:

https://spaceweatherarchive.com/2018/01/22/blue-moon-lunar-eclipse/

http://www.skyandtelescope.com/observing/january-lunar-eclipse/

For this eclipse, people on the eastern portion of North America can watch the beginning stages of the eclipse.  However, the Moon will set before it is totally covered.  For those to the west (i.e. from North America, across the Pacific Ocean, and through most of Asia), the total eclipse will be visible.  For detailed visibility maps, see:

https://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2018Jan31T.pdf

As with the total solar eclipse, the simplest viewing techniques are often the most enjoyable.  While going about your other activities, you can go outside from time to time, and see the progress.  And, there is no law against staying inside and watching through a window!

When the eclipse is total, the Moon is illuminated by a small amount of sunlight which is “scattered” by Earth’s atmosphere.  If you were standing on the Moon, you would see an orange ring around the Earth.  This ring is a view of all the sunrises and sunsets all around the Earth!   This ring of light casts an orange glow onto the Moon.  This strength of the glow is affected by volcanic activity on Earth.  Dust and aerosols from volcanic eruptions can darken the glow so that the Moon will be almost invisible.

Enjoy the Lunar eclipse and keep looking up!

John

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