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:
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.
- Fall '08