CHSI

Have Instruments, Will Travel

Exploring Harvard's Observations of
the Transit of Venus

TRANSITS OF VENUS are rare astronomical alignments in which the planet Venus crosses the face of the Sun as seen from Earth. They occur in pairs (eight years apart) separated at intervals of 105.5 and 121.5 years.

In 1717, astronomer Edmond Halley explained how simultaneous observations of a transit from far flung places could be used to calculate the distance from the Earth to the Sun. He urged astronomers to collaborate in order to determine the dimensions of the solar system–one of the great unsolved problems of the day!

In response, many astronomers sailed to remote parts of the world in order to observe the transits of 1761 and 1769. Harvard professor John Winthrop observed the first from St. John's, Newfoundland, and the second from Harvard Yard.

In recognition of Harvard's important role in transit viewing history, Currator Sara Schechner has assembled a special collection of the instruments involved in the two Winthrop expeditions in Waywiser, our online database.