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Old 05-23-2021, 06:03 AM
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Exclamation Explained: What Astronauts On The Moon Would See And Feel During This Week’s Total Lu

Explained: What Astronauts On The Moon Would See And Feel During This Week’s Total Lunar Eclipse
By: Jamie Carter - Forbes News - 05-22-21

A Nasa scientific visualization of such an event:

This Wednesday’s total lunar eclipse—the so-called “Blood Moon”—will see the lunar surface turn a reddish-copper color for 14 minutes and 30 seconds.

Since Earth will be aligned with the Sun and the Moon, our atmosphere will filter the Sun’s light onto the Moon as it enters the Earth’s shadow, essentially projecting thousands of sunrises and sunsets onto the lunar surface.

That’s the glowing red full Moon those west of the Mississippi will see in the early hours of Wednesday, May 26, 2021, but what would the event look like from the Moon’s surface itself?

It would be nothing less than a total eclipse of the Sun by the Earth!

With Earth hiding the Sun, astronauts on the surface would see a red ring—the sum of all Earth’s sunrises and sunsets—around the limb of the Earth.

“You would look up and see the Earth, potentially also the city lights on Earth, and you would notice the ground around you turn red,” said Dr. Noah Petro, Project Scientist for NASA’s Lunar Reconnaissance Orbiter mission that’s currently orbiting the Moon.

It would also get really cold.

“The lunar surface then cools down substantially during an eclipse as the Moon goes from intense midday Sun to being in darkness,” said Petro. “Hopefully you wouldn’t feel the cooling through your spacesuit.” However, the ground around would cool substantially.

“It would be a pretty immersive affect the same way as on on Earth during a total solar eclipse when shadows look different and the atmosphere around you cools,” said Petro.

A lunar eclipse can be a risky time to have a space mission on the Moon.

NASA is planning to send astronauts to the Moon in late 2024, though that could and probably will slip—and there are two total lunar eclipses in 2025 and one in 2026.

“It depends on what that mission and its experiments are designed to survive, but it puts your equipment into a totally different thermal regime,” said Petro. “During the Apollo missions the astronauts were not going to be on the Moon during an eclipse, but the experiments they left behind were.”

Day-night cycles are, of course, normal on the Moon. “The one big difference of course, is that it's gets really hot and then it gets cold really quickly, so that thermal change is pretty dramatic—and dramatic temperature shifts can do strange things,” said Petro, mentioning windshields that crack in temperature extremes.

Video of 09-27-15 Total Lunar Eclips:

Plenty of science can be done during a total lunar eclipse and NASA’s Lunar Reconnaissance Orbiter (LRO) will, on Wednesday, measure the temperature change on the lunar surface.

Will it survive the sudden onset of cold?

With no sunlight to shine on the solar panels that power its heaters, a spacecraft in orbit can freeze during a total lunar eclipse unless it’s been specifically designed to cope with that challenge.

The LRO is designed to withstand an eclipse.“We've been at the Moon now for 12 years so we’ve gone through a number of eclipses and we know how the spacecraft will respond,” said Petro. “But early on in the mission, we didn’t, so we were very cautious.”

NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE)—a robotic probe that orbited the Moon in 2013/2014—was purposefully designed not to withstand a total lunar eclipse, but it just managed to survive, regardless.

“Because it’s a very short eclipse we know that the battery will not completely deplete during the eclipse and so we can leave the one experiment on to measure the temperature change,” said Petro about LRO this week. “If it were a longer eclipse we might not do it,”

So for missions to the Moon lunar eclipses have become engineering mileposts that have to be planned for in advance.

A total lunar eclipse occurs when a full Moon passes through Earth’s 870,000 miles/1.4 million km long shadow in space. That happens just occasionally, and it can take anywhere from 105 minutes (like in 2018) to just five minutes (like in 2015).

On May 26, 2021 it will last for such a short time because instead of traveling through the center of Earth’s shadow it will pass through its northern part, just 21 miles (34 km) from its outer edge. So the Moon’s northern limb is predicted to be rather bright during totality.

Either way, it’s an event not to be missed if you happen to be on the night-side of Earth at the right time.

Wishing you clear skies and wide eyes.

About this writer: Jamie Carter: I'm an experienced science, technology and travel journalist and stargazer writing about exploring the night sky, solar and lunar eclipses, moon-gazing, astro-travel, astronomy and space exploration. I'm the editor of and the author of "A Stargazing Program for Beginners: A Pocket Field Guide" (Springer, 2015), as well as many eclipse-chasing guides.

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