ay45c1-page4 - 1.2.2 Parallax of Mars transits of Venus...

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Unformatted text preview: 1.2.2 Parallax of Mars, transits of Venus determine scale Putting a scale on things requires that any one distance be known both in AU and in km. 1671: French expedition to Cayenne (French Guiana, home of hot peppers) measured parallax of Mars at opposition: France Background stars Mars Cayenne Not to scale Of course,what is actually seen is: France: Cayenne: Mars Mars They got the answer wrong (or right!) to  10%. [Technology aside: Micrometer sights were rst used in the 1670's.] Halley, in 1716 (age 60) pointed out that the \transit of Venus" in 1761 and 1769 could be used. He knew he would be dead by then and told all young astronomers about it. (These transits are quite infrequent: next ones were 1874, 1882, June 7, 2004, June 5, 2012.) Earth 0.72 AU d Venus D 1 AU 4 Sun ...
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This document was uploaded on 11/02/2011 for the course AST 345 at SUNY Stony Brook.

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