Talk:Stephenson:Neal:Quicksilver:222:The sun becomes an oval (John B.)

From the Quicksilver Metaweb.

Thanks John B. for this annotation. It's interesting. The premise of Hooke's experiment, if I recall it correctly, was that he couldn't get sufficiently precise observations if his telescope was aimed near the horizon, and so he wanted to point it vertically. It would be interesting to know whether his reasoning on this was bogus (i.e. was Hooke unduly influenced by optical illusions) or solid (i.e. is refraction enough of an issue that he really would not have been able to measure parallax well near the horizon).Nealstephenson 11:09, 6 Oct 2003 (PDT)

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There is a detailed discussion of Hooke's parallax measurement attempts in chapter 8 of "Parallax - The Race to Measure the Cosmos" by Alan W. Hirschfeld. The whole chapter describes Hooke's attempts to measure the parallax of gamma draconis using his "Archimedean Engine", the fixed vertical telescope he built at Gresham's College. He gave up when the lens on the telescope broke, but declared that he had results which justified a parallax of 30 arcseconds (somewhat less than 1/100 of a degree) which is more than 1000 times the modern measurement !

On page 144 Hirschfeld states that the atmospheric refraction near the horizon can be up to half a degree (a whole moon's width) this is certainly enough to destroy any attempt at parallax measurement !

jcownie 10:45pm 2 Jan 2004 (GMT)