On June 5th a rare transit of Venus will occur that can be seen from most of North America.  During the transit, Venus can be seen from Earth as a small black dot moving across the sun.  A transit, in which Venus passes directly between the Sun and Earth, is exceptional in that it occurs about twice every hundred years, usually eight years apart. Because of their infrequency, humans are thought to have noted only six transits of Venus: 1639, 1761, 1769, 1874, 1882 and 2004.  The next one will not occur until 2117. Historically theses transits were anticipated and studied by astronomers all over the world as the transits helped determine the distance from the Earth to the Sun.  The New-York Historical Society’s library has many forms of documentation of  efforts to view and study these past transits of Venus.

Portrait of William Alexander (Lord Stirling), PR 52, Portrait File

William Alexander was an keen observer on the transit of Venus from 1769. This transit was important because it was one of the first times that a transit was being observed from many places in the New World.  William Alexander came from a prominent family and was appointed Surveyor-General of the Province of New Jersey. He went on to be a major general in the Revolutionary War and is also known for claiming the title of the Earl of Stirling. Although this title was disputed and was never recognized by British House of Lords, he continued to go by Lord Stirling throughout his life.  Skilled in astronomy, William Alexander observed and made careful notes on the 1769 transit from his residence manor in Basking Ridge, New Jersey. See here for more information on N-YHS’s collection of the Alexander Family Papers.

Notes of William Alexander on the preparations for the upcoming Transit of Venus, MS 758

Chatham Island Scientific Party, PR 020, Geographic File, New Zealand

Another transit of Venus documented in our collections is  the American expedition to Chatham Island in New Zealand to view the 1874 transit. This expedition was unfortunately ill-fated. It was led by Edwin Smith and included an Assistant Astronomer, three Photographic Assistants, and an Instrument Maker. On the way to Chatham Island, the main photographer died of yellow fever and surviving members of the party experienced difficulty in setting up the pier for the photographic plate holder.

Equatorial House on Chatham Island, PR 020, Geographic File, New Zealand

During the transit, the sun was mostly obscured by clouds. This and bad timekeeping all led to the expedition producing the poorest observations of all the eight American expeditions sent around the world. Thankfully for us, the photographers had better luck photographing the expedition than they did the transit.

If you plan on viewing the transit on Tuesday, take precautions to view it safely, just like astronomers in the past.  The Planetarium at the Museum of Natural History will have a live simulcast of this rare transit from the Mauna Kea Observatory in Hawaii. Or if you are in the Philadelphia area, check out  events at the American Philosophical Society relating to the transit.