Scholla: The Transit of Venus-1769 6/27/1941
David Rittenhouse, the first American astronomer, was a man of many parts. In 1760 he surveyed the boundary line between Pennsylvania and Maryland with crude instruments which he devised. When Mason and Dixon established their famous line in 1763, they found that the previous surveys by Rittenhouse were correct in every detail. In 1794 Rittenhouse accompanied President Washington and other distinguished men in a journey into Berks and Lebanon Counties. It was he who made the original surveys for the Union Canal which followed the Tulpehocken creek through western Berks and joined with the Schuykill near Reading.
Among the great achievements of the colonial astronomer was the construction of an instrument with which to observe the transit of Venus across the sun. This astronomical event occurs at rare intervals. There has been only one transit since 1769, when Rittenhouse made his observations, and the next phenomena is scheduled to take place in the year 2012.
The importance of securing these observations may be understood if we keep in mind that in 1769 a transit of the planet Venus furnished the most accurate method for measuring the distance from the earth to the sun in terms of miles, and that distance served as the yardstick which the size of all planets was measured. If this data had not been made available in 1769 the world would have been forced to wait until the next transit, in 1882, to learn these vital facts. There were several observers in Europe who made diligent preparations to record the event of two centuries ago, but it happened that June 3, 1769 was overcast in Europe and scholars there had no chance to make their observations.
The weather was perfect in Pennsylvania and conditions were ideal for the task to which Rittenhouse and his associates had set themselves. With the instrument which he had made with his own hands the astronomer made his observations at his home in Norriton, near Philadelphia. It is recorded that when the great task was completed and known to be successful Rittenhouse swooned away. So great was his relief after weeks of planning and anxiety.
The undertaking was sponsored by the American Philosophical Society. Three observation stations were set up. In addition to the one at Norriton observers were placed at the State House (Independence Hall) and in Lewes Delaware. The instrument which Rittenhouse made and used to such great advantage is now on exhibit in the rooms of the American Philosophical Society in Philadelphia.
“Astronomers are greater men than politicians” said Thomas Jefferson in a tribute to Rittenhouse “because they find new worlds while politicians find only new governments.”
Graeff, Arthur D. Scholla: Transit of Venus 1769. Reading Times. June 27, 1941