What is a transit in astronomy?
Quick Answer
A transit is when one celestial body passes directly in front of another as seen from an observer. In the Solar System, Mercury and Venus can transit the Sun from Earth’s viewpoint.
The Full Story
Astronomical transits are useful because they reveal alignment and size relationships. A planetary transit across a star causes a tiny dip in the star’s brightness, which is how many exoplanets are discovered. In our Solar System, Mercury transits the Sun much more often than Venus because Mercury’s orbit is smaller and more closely aligned with Earth’s viewing geometry. Transits of Venus are rare, appearing in pairs separated by more than a century.
Key Facts
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"The alignment trick astronomers use to find distant planets"
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