Sunday, May 27, 2012

Transit Trivia: David Rittenhouse

The above image is a portrait of the American astronomer, inventor, mathematician, surveyor, scientific instrument craftsman, and public official, David Rittenhouse (1732 - 1796). The portrait includes a telescope of his own construction. The portrait was painted in 1796 by Charles Willson Peale (1741–1827) and is part of the Smithonian National Portrait Gallery. Image Credit: The image is in the Public Domain.

When Pennsylvanian David Rittenhouse was very young, his uncle died and left David his carpentry tools and instructional books. David used these to begin a career as an inventor. He also enjoyed building scale models. Rittenhouse was self-taught and showed great ability in science and mathematics. By the age of 13, Rittenhouse had mastered Isaac Newton's laws of motion and gravity.

When he was 19, Rittenhouse started a scientific instrument shop at his father's farm. His skill with instruments, particularly clocks, led Rittenhouse to construct two orreries (scale models of the solar system) for Rutgers University in New Jersey. In return for the gift, the college gave him a scholarship to attend the college, enabling him to obtain a degree in philosophy.

At the age of 28, Rittenhouse published his first mathematical paper. This would be one of many he published throughout his life.

Rittenhouse was one of the first to build a telescope in the United States. He used natural spider silk to form the reticle for the instrument, he used im his own observatory on his family farm.

In 1768, Rittenhouse was elected to membership in the American Philosophical Society, where he served as librarian, secretary and, following the death of Benjamin Franklin in 1790, vice president.

In the year that he joined, Rittenhouse announced to the Society his plans to observe the pending transit of Venus from several locations. In favor of the plan, the Society persuaded the legislature to grant 100 toward the purchase of new telescopes, and Society members volunteered to staff half of the 22 telescope stations. Rittenhouse worked tirelessly for a year in preparation for the event, even to the point of becoming ill a week before the appointed day.

Rittenhouse rallied before June 3rd and was able to begin his observations on time, but he fainted during the transit. Lying on his back beneath his telescope, trained at the afternoon sun, Rittenhouse regained consciousness after a few minutes and continued his observations. Rittenhouse's account of the transit, which was published in the American Philosophical Society's Transactions, does not mention his fainting, but it is otherwise meticulous in its documentation.

Rittenhouse used the observations to calculate a distance from Earth to the Sun of 93-million miles. (This is the approximate average distance between Earth and the Sun.) The published report of the transit was hailed by European scientists, and Rittenhouse would go on to correspond with famous contemporary astronomers, such as Jérôme Lalande and Franz Xaver von Zach.

There are many tributes to the work of David Rittenhouse. Outside of his Philadelphia farm house is an historic marker commemorating Rittenhouse's observations of, and the resulting calculations from, the 1769 transit of Venus. Elsewhere in the town, one of William Penn's original city squares — Southwest Square — was renamed Rittenhouse Square. And nearby, on Walnut Street, the University of Pennsylvania houses its Physics and Mathematics departments in the David Rittenhouse Laboratory.

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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