The sun and the moon look the same size in the sky because they are of equal size and distance from Earth.
This is untrue. We know from years of observation that the sun is about 400 times larger in diameter than the moon, and also happens to be about 400 times further away.
The moon and the sun are not the same size, contrary to a claim made on Facebook and X (formerly Twitter).
The posts say: “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. 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.”
But this is not true, and is contradicted by evidence established over thousands of years.
The reason the sun and Earth appear the same size is because the sun is roughly 400 times farther away than the moon, and—as the Facebook post says—also about 400 times bigger in diameter. This is a complete coincidence.
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The sun lies at the centre of the solar system where it dwarfs all other objects. It holds 99.8% of the solar system’s mass and is roughly 109 times the diameter of the Earth.
About one million Earths could fit inside the sun. The sun’s radius—the distance from the edge to the centre—is 432,450 miles, making its diameter about 864,938 miles.
And scientists are now investigating whether the sun could be slightly larger than previously established.
On the other hand, the moon, Earth’s only natural satellite, has a diameter of only about 2,159 miles.
The fact that the sun and moon are different distances away from the Earth was recorded by astronomers in Ancient Greece, with the distance from our planet to the moon determined with some accuracy during the 2nd century BC.
A fairly accurate distance between the Earth and the sun was calculated in 1771 by observing the transit of Venus (when the planet’s silhouette passes in front of the sun). It has since been established as about 93 million miles on average.
The average distance between the Earth and the moon is 238,855 miles. This number varies over the 27.3 days it takes for the moon to go round the Earth, as its orbit isn’t a perfect circle.
We have previously debunked other false claims about space, including that the Earth is flat, and that a large asteroid was projected to collide with our planet last year.
Image courtesy of Sebastien Lebrigand
This article is part of our work fact checking potentially false pictures, videos and stories on Facebook. You can read more about this—and find out how to report Facebook content—here. For the purposes of that scheme, we’ve rated this claim as false because the sun is not the same size as the moon or the same distance from Earth, but vastly bigger and further away.
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