Phases of Venus

The phases of Venus vary from a thin crescent to full phase in 584 days.

Related Topics:
Phases - Venus

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They can be seen without a telescope by those with exceptionally acute eye-sight, at the limit of human perception. The angular resolution of the naked eye is about 1 minute of arc. The apparent disk of Venus measures between 60.2 and 68 seconds of arc, according to the distance from Earth. Nevertheless it is possible for observers with an extreme acute eyesight to see a crescent Venus under ideal atmospheric circumstances.

Related Topics:
Telescope - Angular resolution - Seconds of arc

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There have been numerous reports stating such observations. The phases of Venus were apparently already seen in Mesopotamian times by priest-astronomers. Ishtar (Venus) is being described in cuneiform text as 'having horns'.

Related Topics:
Mesopotamia - Ishtar - Cuneiform

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The first written record of the phases of Venus comes from Galileo in his book 'The Starry Messenger' of 1610. They were however observed with a telescope. The existence of these phases was proof to him that Venus was orbiting the Sun and not the Earth, and that the orbit of Venus was situated between Earth and the sun. This was a confirmation of the heliocentric model, advocated by Copernicus in 1543 in his book in De revolutionibus orbium caelestium ('On the Revolution of Heavenly Spheres'). Furthermore, it proved than the planets appear to "shine" by reflecting light from the sun.

Related Topics:
Galileo - Heliocentric - Copernicus

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