Read more at —

 

Discovery of Neptune (Wikipedia)

 

Discovery of planets (St Andrews)

 

How Britain put the spin on Neptune  (Guardian review)

 

The Case of the Pilfered Planet  (Scientific American)

 

Books —

 

Tom Standage  ‘The Neptune File’ Berkley 2000

 

Morton Grosser  ‘The Discovery of Neptune’  Dover Pub. 1978

 

Flamsteed Astronomy Society

Huygens, Halley & Harrison

— Anniversaries 2006

1846, September 23rd — 160 years ago the planet Neptune was discovered by Johann Gottfried Galle and Heinrich Louis d’Arrest working at the Berlin Observatory.  They were deliberately searching for a previously unrecognised planet in a small area calculated by the French astronomer-mathematician Urbain LeVerrier.  His impressive prediction was the culmination of the work of many astronomers following the discovery of the first planet in recorded history :  the planet Uranus, found by the British astronomer William Herschel working in Bath on March 13th, 1781.   As Uranus was carefully observed over the following 65 years it became clear that its orbit persistently refused to follow the path calculated from Newton’s law, including adjustments for the disturbances (perturbations) caused by the giant planets Jupiter and Saturn, inside Uranus’s orbit.   Various explanations were proposed, including the existence of an unrecognised planet outside the orbit of Uranus.  LeVerrier was a proven master of the complex calculations needed to work backwards from the discrepancies in Uranus’s orbit and deduce the size, orbit and present position of the unrecognised planet, if indeed it existed.  He began working very systematically on the problem and presented a preliminary paper in Paris in November 1845.  LeVerrier distributed all his papers to leading astronomers across Europe including the Astronomer Royal in Greenwich, George Airy.  Airy’s replies expressed great interest and encouragement.  By summer 1846 LeVerrier had completed the calculations needed to predict the alleged planet’s approximate size and present position.  He correctly surmised that the Berlin Observatory would be the one most likely willing to interrupt its regular programme and conduct a search.  Johann Galle there was keen to do so and persuaded the director Enke to let him.  Helped by a young assistant, Louis d’Arrest, they luckily had access to a newly published star chart of the exact area given by Le Verrier.  On the very first night of their search they found the planet : “That star is not on the map!”

Such a discovery, based on a calculated prediction, would have been sensational enough, but the entire episode then blew-up into an international incident.  Out of the blue (so far as the rest of the world was concerned), George Airy announced that the same calculation had already been done, before LeVerrier, by a young Cambridge mathematician John Couch Adams.   Airy had asked Prof James Challis to search for the planet where predicted by Adams (using the Cambridge Northumberland telescope because Greenwich didn’t have a suitable instrument).  Challis had dragged his feet and been pipped to the post by lucky Berlin — but luck favours the well-prepared.  Apparently Airy had known about Adam’s work since October 1845 but hadn’t said anything about it except to a few of the Cambridge ‘inner circle’.  The Cambridge astronomers campaigned for Adams to be recognised as co-discoverer.  The French indignantly rejected the claims.  As the astronomers developed a slanging match over who had done what first, the media had a field day.  The French newspapers accused perfide Albion of trying to muscle-in on the action.  Airy and Challis were castigated by the British press for fumbling the ball —  clearly, discovering new planets should have been a British thing.  Recent research suggests that the British claim is murky.  It would appear that Adams had indeed completed a calculation ahead of LeVerrier but whether his early predictions had sufficient precision for a successful search is in some doubt.  Airy was at least guilty of being too busy, attempting to engineer a ‘one-two’ prediction and discovery for Cambridge, and then may well have over-egged the case for Adams.

One positive outcome was that Airy decided Greenwich must have a suitable telescope to do such searches itself in future.  He got funding for the Great Equatorial Building which originally from 1860 housed the 12.75-in Merz refractor.  In 1894 this was replaced by the 28-in refractor there today.

 

Johann Galle 1812-1910

Two more 2006 astro-anniversaries — these two shouldn’t be forgotten, and one has distinct Greenwich involvement, but neither benefit from the advantages of superb alliteration, like those on the previous pages.   First Neptune —

Urbain Le Verrier 1811-1877

John Couch Adams  1819-1892

George Biddell Airy 1801-1892

James Challis 1803-1882

Turn over for one more 2006 anniversary

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