Artemis astronaut Jessica Watkins marvels at the moon from space station (photo)

Aug 6, 2020
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Ms. Watkins writes...

"Every moonset on @Space_Station brings us one step closer to earthrise on the moon"

...and I would hope if she is lucky enough to get there she learns more about our largest natural satellite before she does.

There is no "Earthrise" on the Moon. You may have thought you saw film of one taken by Bill Anders on Apollo 8, but that's because it was taken from a spacecraft orbiting the Moon.

Because the Moon is tidally locked with the Earth, while you'll see our home planet go through phases like the Moon, it hangs eternally in the same spot in the lunar sky, day after day, month after month, year after year, albeit with a bit of a wobble.
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I'm going to give her some credit for thinking about seeing "Earthrise" from lunar orbit in the same way that she is currently seeing "moonset" from the space station, now.

But, nope, she is not going to see the Earth "set" from a base on the moon itself.
The Moon librates 6.5° north-south due to its orbital plane being tilted and east-west 7° due to a varying orbital speed due to an eccentric orbit. The Earth subtends 1/2° as seen from the Moon so there will be an Earth rise and Earth set seen each month from both the east and west edges and from the poles.

Here is an animation showing the movement:
Lunar Libration - Bing video
Well, OK, if somebody has the luxuries of placement and time to stand in the right place and watch for a day or so, just to see the Earth go from completely below the horizon to completely above the horizon. I suspect astronauts on the moon would be too busy to watch the whole transition.

But, what exactly is "moonrise" here on Earth, anyway. Most people think of it simply as the moon being near the horizon on its way "up", where it has an illusionary effect of looking bigger. At the right places on the moon , that would be a nearly constant condition, rather than a short term transient event.

The picture that most people think of as "Earthrise on the Moon" was taken from Apollo 8 as it rounded the Moon without ever sending down a lander. See .
Yes, we assume that someone has the luxuries of placement and time to see the Earth go from completely below the Moon's horizon to completely above. This would involve a 1/2 degree movement out of a 14 degree circuit over a one month period. It would take about 24 hours for the Earthrise to be witnessed. It would take lots of coffee, but it could be done. Now the question becomes: Is there enough coffee on the Moon to make this happen? I believe Philip Huggan could probably expound upon that question.

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