They Told The Story
A Neptune Chronology
Adams Dated Computations
The Forgotten Diary
Within One Degree
The Crown Jewels Document
Announcing The Discovery
Challis' Unseen Testimony
A Retrospective History
A Cantab. Clique
Adam's July Ephemeris
Mapless In Cambridge
Airy Tells the Truth
The Radius Vector: A Trivial Question?
Airy Blows His Top
Eggen Takes the Papers
Selected Correspondence
Primary Sources
Related Links.



Soon the ideal excuse appeared, as to why Challis had failed to find Neptune. He hadn’t got the map. The new Berlin Sternkalendar (Hour 21, by Bremiker) covering the zone of the heavens in which it was discovered, had not yet been distributed: only the Berlin Observatory owned a copy. This explanation was mentioned by Challis in a Oct. 17th letter to the Athenaeum, and developed in his presentation to the RAS on November 13th, 1846:

‘If I had had this map [Hour 21], a first sweep would have been unnecessary: I should have compared my field of view with the map at once.’

The Dec 5th editorial of The Athenaeum made this issue central:
‘if the Cambridge library had possessed the twenty-first hour of the Berlin star-maps, Adams and Leverrier would have changed places.’

(This Editorial was by Augustus de Morgan, as his wife Sophie later disclosed in her biography). It became a central part of the story, e.g. Smart wrote in 1946:
‘There can be no doubt that if the star-chart had been distributed immediately after it had been engraved, Challis’s labours would have been immeasurably reduced and discovery at Cambridge would have been almost certain.’ (p.80)

Meanwhile, back in the real world, Challis owned the Hour 22 Berlin star-map, and Neptune was on that map for the first four weeks of his sky-search. ‘Hours’ here allude to Greenwich Hour Angles, of which twenty-four comprise the circle of Right Ascension. Each map therefore spanned fifteen degrees, with the hours subdivided into sixty ‘minutes’ and each map having an overlap zone of four minutes (‘Four minutes’ here equal one degree). Neptune, moving retrograde, exited from the map ‘Hour 22’ onto the ‘Hour 21’ towards the end of August 1846. Thus Challis had a good four weeks of his sky-search while Neptune was on the map in his possession. Only after this, in September, was map ‘Hour 21’ required.

His October 17th letter to the Athenaeum specified the two positions of what he later recognized as Neptune:

Aug 4th : RA 21h 58min, Aug 12th : RA 21h 57 m

These parameters were on the ‘Hour 22’ map which he presumably had in front of him, because the ‘Hour 22’ map extended out to 21h 56m (For comparison, when Challis started on July 29th Neptune was at 21h 59m GHA, then by Sept 23, still moving retrograde, it was at 21h 53m GHA).

For Galle and D’Arrest In Berlin the new star-map was indeed crucial. As Encke, the Berlin Observatory’s Director, wrote to M.Arago in Paris:

‘Sans cette circonstance infiniment favourable ... sans une carte où l’on pût être sûr de trouver les étoiles fixes jusqu’à la dixième grandeur, je ne crois pas qu’on eût trouvé la planète.’ (Comptes Rendues 12th October, p.662)