Monday, May 21, 2012

Transit Trivia: The Challenges of 1761

During the 1761 transit of Venus, astronomers observed the event from about sixty locations around the world. In addition to Mason and Dixon observing at the Cape of Good Hope, and Lomonosov observing from St. Petersburg, Russia, the list of others reads like an astronomical Who’s Who of the day.

French astronomer Jean-Baptiste Chappe d'Auteroche (1722 – 1769) was chosen to go to Tobolsk in Central Siberia. The trip was arduous and Chappe arrived in Tobolsk with little time to spare, although he was able to observe the lunar eclipse of May 18th, which enabled him to calculate the longitude of Tobolsk. The spring floods of the Tobol and Irtysh rivers had been particularly severe that year, and some of the local peasants blamed the foreigner with his strange equipment who was "messing with the Sun": Chappe had to be protected by a cordon of armed Cossacks to make his observations. Fortunately, the weather conditions were excellent, and Chappe was able to observe the entire transit. He published his results from Saint Petersburg (Mémoire du passage de Vénus sur le soleil, avec des observations sur l'astronomie et la déclinaison de la boussole faites à Tobolsk, en Sibérie), and did not return to France until 1763.

French astronomer, priest, and naval geographer Alexandre Guy Pingré (1711 – 1796) was chosen to observe on Rodrigues Island near Madagascar, of the southeastern coast of Africa. Pingré had poor eyesight, but outstanding mathematic skills. As it turned out, the visibility of the transit from this location was less than ideal.

American mathematician, physicist and astronomer John Winthrop (1714 - 1779) observed from St. Johns, Nova Scotia. Winthrop traveled there in a ship provided by the Province of Massachusetts - probably the first scientific expedition ever sent out by any incipient American state.

French astronomer and cartographer César-François Cassini de Thury (1714 – 1784) observed at Vienna in Austria. Cassini de Thury was a grandson of Giovanni Domenico Cassini, and would become the father of Jean-Dominique, comte de Cassini.

Many observers failed to get to their primary observing sites due to military action of the ongoing Seven Years’ War. For instance, Mason and Dixon were traveling to Bencoolen in Sumatra, but settled for the Cape of Good Hope.

French astronomer Guillaume Le Gentil (1725 – 1792) tried to reach Pondicherry in India. When his expedition had nearly arrived they learned that the British had occupied Pondicherry, so the frigate was obliged to return to Île de France. On June 6, the day of the transit, came, and the sky was clear, but he could not take astronomical observations with the vessel rolling about. After having come this far, he thought he might as well wait for the next transit of Venus, which would come in 1769.

The next transit of Venus will occur over June 5-6. To learn more, visit these links.

2012 Transit of Venus, NASA/Goddard Space Flight Center:

Transit of Venus, Sun-Earth Day 2012, NASA:


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