ay45c1-page5 - Note there is a geometrical magni cation...

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Unformatted text preview: Note there is a geometrical magni cation factor that helps: D = 0:72 : d 0:28 So from di erent latitudes on  one sees di erent tracks. Separation is here exaggerated! It is only ~ 1 Venus diameter. Sun How to measure small separation from opposite sides of globe? Not by subtracting measurements of height from \top" of sun | too imprecise. Rather, take the average height to get the geometry, and use the di erence of transit ingress/egress times or durations to infer the small di erences. Order of magnitude (ignoring magni cation factors, geometry, etc.):  and diameters  12000 km  104 km + diameter  1:5  106 km  106 km +  velocity  10 km= s ) 103 s to move diameter, 105 s  1 day to move across + In 1761 and 1769 various discrepant results 10% were obtained. Not until 1835 was an accurate value obtained (by Encke) from these same measurements: Gauss had, in the meanwhile, discovered least squares tting for combining observations! 5 ...
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