April 25, 2009

Twin Crescents, Critical Observation

image by Jorge Figueroa, Guatemala City, Guatemala

In 1610 when Galileo made humanity's first telescopic observation of Venus he followed the planet long enough to see it change its shape. He realized that it was exhibiting phases, just as the Moon does. This was perhaps Galileo's most important discovery for solar system science because it disproved the Ptolemaic theory that Venus was always between Earth and Sun. Galileo recognized from his discovery of Venus' phases that sometimes Venus was on the opposite side of the Sun from the Earth. Copernicus was right*, Ptolemy was wrong and Galileo proved it.

Chuck Wood

• Tycho's theory of the solar system was wrong, but in it Venus showed phases.
  

Technical Details
This is the first LPOD from Guatemala!
April 22, 2009, 5:33. Canon XTi, 1/80sec, ISO 200, prime focus at Takahashi FS 78 Refractor.

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