Does Mt. Everest cast a shadow on the moon? (Intermediate)

Does Mt. Everest cast a shadow on the moon? If yes,where can I see it in "black and white". Thank you for your effort, I've had no luck

The answer to this is a very definite yes and no!

Ignoring the effects of the Earth's atmosphere (which I have no idea how to take into account), and assuming the Moon has a smooth surface (which I'll comment on below) the shadow of the Earth on the Moon would not have a sharp edge, but would be bumpy due to variations in height of the Earth. Every once in a while the Earth-Moon system would be set up such that Mount Everest is on the edge of the shadow of the Earth on the Moon. Mount Everest has a peak elevation of 29,035 feet (8850 meters, see Mnt Everest), or 0.1% of the radius of the Earth (which at the equator is 6378.137 km or 3963.19 miles), so the bump on the shadow would stick out by about 0.1% of the radius of the shadow. This is the largest the shadow of Everest could ever be.

The next question to ask is if that is large enough to be visible. Lots of clever things have been done in the past by measuring the radius of the Earth's shadow on the Moon. Check it out: Measuring the Solar System.

The ancient Greeks knew that the radius of the Earth's shadow on the Moon was about twice that of the Moon itself (a fact which they used to find an estimate of the distance to the Moon among other things). The angular radius of the Moon is 0.25 degrees, so the angular radius of the Earth's shadow in the Moon is about 0.5 degrees, so the angular size of the shadow of Mount Everest on the Moon is about 2 arcseconds (where an arcsecond is 1/3600 of a degree). This is barely visible using a good telescope in a place where our atmosphere doesn't create too much "twinkling" of the stars.

But we assume that the Moon is smooth - which it is not. The mountains and craters on the Moon will create bumps and wiggles at the edge of the Earth's shadow which I think would completely hide the shadow of Mount Everest. Also (as I said above), I'm not sure of the effect of the Earth's atmosphere. It might blur out the edges of the shadow anyway (because of refraction of light from the Sun).

So I suspect that while technically Mt Everest does sometimes cast a shadow on the Moon, it could not actually be seen.

This page was last updated on July 18, 2015.

About the Author

Karen Masters

Karen Masters

Karen was a graduate student at Cornell from 2000-2005. She went on to work as a researcher in galaxy redshift surveys at Harvard University, and is now on the Faculty at the University of Portsmouth back in her home country of the UK. Her research lately has focused on using the morphology of galaxies to give clues to their formation and evolution. She is the Project Scientist for the Galaxy Zoo project.

Twitter:  @KarenLMasters

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