• noun the apparent movement of a star or planet across the meridian from which it is being observed, caused by Earth’s rotation
  • Passage of Mercury or Venus across the face of the Sun, as seen from the Earth, or of any astronomical body across the meridian. Transits of Mercury and Venus were observed closely in early attempts to discover the size of the astronomical unit, and hence the scale of the solar system, by timing transits as seen from different points on the Earth, whose distance apart was known.

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