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Astroboffins capture video of Mercury passing across the Sun's surface

Daedalus Silver badge

It has to happen when Mercury crosses the ecliptic, which is the plane of Earth's orbit. Mercury's orbit is inclined at 7 degrees to the ecliptic and the apparent diameter of the Sun from Earth is 0.5 degrees, so the alignment doesn't happen easily. Also the Earth has to be in the right place in its orbit, which is a space about the diameter of the Sun across: 800,000 miles: that's about a 15 hour window.

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