The Orange Lunar Eclipse

This week's lunar eclipse was the most orange one that I have ever seen. A lunar eclipse is when the earth casts it's shadow on the moon and a solar eclipse is when the moon casts it's shadow on the earth. There is a difference of about five angular degrees between the plane of the moon's orbit around the earth and that of the earth's orbit around the sun. If the two were in exactly the same plane then there would be both a lunar and a solar eclipse every month.

The orange or red color of the moon that is often seen during a lunar eclipse is due to light from the sun being refracted through earth's atmosphere before it reaches the moon. The blue end of the spectrum is of the shortest wavelength and is thus refracted the most. The red-orange end of the spectrum is of the longest wavelength and is thus refracted the least. 

The following diagram, which is not to scale, shows how sunlight is refracted by earth's atmosphere. The blue light (outer lines) is reflected the most so that it misses the moon. The red or orange light (inner lines) is refracted less so that it reaches the moon. Whether the red or orange light reaches the moon depends on the exact angle between the plane of the earth's orbit around the sun and the plane of the moon's orbit around the earth.

Here is a link to the posting about eclipses, that I wrote last year before the solar eclipse.

www.markmeeksideas.blogspot.com/2024/02/eclipses-and-associated-science.html?m=0