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Despite appearences from Earth's surface, the sun is larger than the moon | Fact check

Kate S. Petersen   Paste BN
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The claim: The sun and the moon are the same size and the same distance from Earth

A Dec. 28, 2023, Facebook post (direct link, archive link) claims humanity's basic understanding of the solar system is flawed.

"They say the sun is 400 times larger than the moon and that it only appears to be the same size as the moon because, miraculously, it is 400 times further away," reads the post. "Occam’s razor states the simplest explanation is usually the best one; they are of equal size and distance from us, and both reside within our local system."

The post was shared more than 100 times within three weeks.

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Our rating: False

The sun and moon are different sizes and located at different distances from the Earth, as confirmed by an array of measurement approaches including radar, lasers and calculations based on planetary movement.

Sun is larger and farther from the Earth than the moon

The sun is around 400 times larger than the moon and also around 400 times farther away from Earth than the moon, according to NASA. Because of this, the moon and the sun may appear to be almost the same size when observed from Earth, such as during a total solar eclipse.

However, at other times, such as during an annular solar eclipse, the sun and moon appear to be different sizes. This is because the moon's orbit around Earth (and Earth's orbit around the sun) are elliptical, so the precise distances between the three bodies change, according to NASA.

An annular solar eclipse occurs when the moon is farther away from Earth in its orbit, making it appear smaller.

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Researchers have confirmed the sun and moon's actual sizes and positions in space through various techniques.

For instance, the distance between Earth and the moon − 238,855 miles on average − has been measured by bouncing radar and lasers off the moon and counting the time it takes for the signal to return to Earth, according to the Institute of Physics. The diameter of the moon − around 2,159 miles − can be calculated mathematically based on the distance from the Earth to the moon and other measurements, Phil Sutton, an astrophysics lecturer at the University of Lincoln, explained on his YouTube channel.

The distance between Earth and the sun (around 93 million miles on average) can be extrapolated from the distance between the Earth and Venus, Jo Dunkley, a Princeton astrophysicist, wrote in "Our Universe: An Astronomer's Guide." This distance can be measured by observing a transit of Venus − the movement of the planet in front of the sun with respect to the Earth − from different positions on Earth.

The distance to Venus can also be measured with radar. The diameter of the sun − about 865,000 miles − can be determined by measuring the amount of time it takes for Mercury to transit in front of the sun.

Paste BN reached out to the Facebook user who shared the post for comment but did not immediately receive a response.

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