Scientists Say: Transit

This is when a planetary body passes in front of a star, or a moon in front of a planet


This is the moon Io in transit across the face of Jupiter.

NASA/JPL/University of Arizona

Transit (noun, “TRAN-sit”)

A transit has a specific meaning in the field of astronomy. It is when a planet, asteroid or moon passes in front of a star. A moon passing in front of a planet is also a transit. To our eyes, a transit usually looks as though a small, dark dot is crossing the face of a star or planet.

Transits are useful to astronomers searching for new planets outside of our solar system. If the scientists see the light from a star dip a little, this could be because a planet is in transit in front of that star.

In a sentence

When an object in transit is big enough to block out the light from the object behind it, scientists call it an eclipse.

This video shows the transit of Venus across the face of the sun, an event that happened in 2012. The next transit will occur more than a century later, in 2117. NASA Goddard

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Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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