Conspiracy theory that moon didn't cause eclipse ignores basic science | Fact check

The claim: Moon not visible before or after eclipse proves 'it's not the moon blocking out the sun'

An April 8 Facebook video (direct link, archive link) shows the sun in the sky alongside text that reads, "Notice something missing from this picture?"

"No one has ever witnessed the approach or departure of the moon during an eclipse," reads more text in the video.

The video shows the moon appearing next to the sun, passing in front of it and reappearing on the other side.

"Have you ever stopped to think that when you see a solar eclipse, you never see the moon before or after the eclipse?" the video's caption reads. "A solar eclipse is not what they taught you in school. Nobody knows exactly what it is, but without a doubt, it's not the moon blocking out the sun."

A similar post on X, formerly Twitter, was reposted more than 1,000 times in five days.

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Our rating: False

A solar eclipse happens when the moon passes between the Earth and the sun and blocks its light. The side of the moon facing Earth is not illuminated during an eclipse. That, along with the brightness of the daytime sky, makes the moon virtually invisible to the human eye.

Dark half of moon faces Earth during solar eclipse

A solar eclipse is, by definition, when the moon passes directly between the Earth and the sun, contrary to the video's claim. It's exactly what you learned in school.

Scientists can predict the timing of eclipses like the one April 8 using computer models that show how the Earth and moon move around the sun.

"Current eclipse forecasts are accurate to less than a minute in time over a span of hundreds of years," NASA's website says.

Fact check: Video claiming to show 'The Simpsons' predict the April 8 eclipse is fabricated

Unlike the sun, the moon doesn't create its own light. Instead, it's visible because light from the sun reflects off its surface, NASA's website says. The sun always lights up half the moon, while the other half remains dark. The amount of the illuminated half that can be seen from Earth changes as the moon travels through its orbit and determines the moon's phase.

"When the moon is about to cross in front of the sun – or cross below or above the sun, as it does most months – this is the phase that we call 'new moon'," Tom Fleming, an astronomy professor at the University of Arizona, told USA TODAY. "At new moon, we are looking at the nighttime side of the moon. The sun is illuminating the side of the moon that is facing away from us."

So with the dark side of the moon facing Earth and scattered blue sunlight lighting up the sky during the day, the moon becomes practically invisible to the human eye, Fleming said.

"The only way we could 'see' the moon at this phase would be if it were to pass directly in front of the sun and block the sunlight coming to us, which is what happened (April 8)," he said.

The "full moon" phase, conversely, is when the moon is opposite the sun in the sky, meaning its light side is directly facing Earth. There are times before and after that phase when the moon can be seen during part of the day.

USA TODAY reached out to the social media user who shared the post for comment but did not immediately receive a response.

Reuters also debunked the claim.

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This article originally appeared on USA TODAY: Moon not visible when light side faces away from Earth | Fact check