The Sky This Week, 2011 July 5 – 12 — Naval Oceanography Portal
The end of the week marks an interesting historical “anniversary†of sorts. On July 12th the far-flung planet Neptune will complete its first full orbit of the Sun since its extraordinary discovery on the night of September 23rd, 1846. On that crisp autumn evening nearly 165 years ago two German astronomers, Johann Galle and Heinrich d’Arrest, pointed the 9-inch refractor at the Berlin Observatory to a patch of sky in the constellation Aquarius where the French mathematician Urbain J.J. Le Verrier predicted that they would find a planet. Using a newly-compiled but unchecked star atlas the astronomers quickly found a “star†that was not on the map about one degree away from the place where the new planet was predicted to be. Careful examination showed the “star†to have a tiny pale blue disc, and thus Neptune was revealed. Le Verrier’s prediction was based on irregular motions of the planet Uranus, and similar reasoning by the English mathematician John Couch Adams led to a similar solution. Neither Adams nor Le Verrier could muster much interest in the search for the planet in their own countries; Le Verrier’s letter to the director of the Berlin Observatory ultimately led to the find. While Galle and d’Arrest are given credit for Neptune’s discovery, they were not the first people to see it. In December of 1612 and January of 1613 none other than the famous Galileo recorded it as a faint background star near Jupiter, but his crude telescope couldn’t show Neptune’s slow movement against the background stars.
The Sky This Week, 2011 July 5 – 12 — Naval Oceanography Portal