In the year 1769 an observatory was built in Philadelphia, just a couple of hundred feet south of Independence Hall. It had been built so that astronomers could observe a transit of the planet Venus that year. A transit occurs when either Mercury or Venus passes directly between the earth and the sun; with protective filters, we see those planets as small, dark round dots against the sun’s face. Transits of Venus are rare; they occur in pairs every hundred and twenty years. Seven years after colonial astronomers saw this transit the observatory was still there, and its balcony made an excellent platform for the first public reading of the Declaration of Independence, on July 8th, 1776. During the Revolutionary War, the Philadelphia observatory housed British troops who occupied the city. And not too many years after the end of the war, the observatory fell into disuse, and sadly, is no longer there.