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A brief history

by Pierre Causeret last modified Jul 11, 2012 05:26 PM
Contributors: Florence Trouillet

Venus is the brightest celestial body in the sky, after the Sun and the . Man has observed it for many thousand years. It is visible in the evening after sunset and before sunrise in the morning.  It can even be seen in daylight if you know where to look and if the atmosphere is transparent enough.

Venus sous Lune

Venus under the Moon

 

It was called Innana (Sumer), Ishtar (Babylon), Aphrodite (Greece), Vesper (in the evening) or Lucifer (in the morning) ... The Mayans had noticed it returned to the same position every 584 days (synodic period). It is also called the Morning Star. In many cultures, Venus represents woman, love and beauty.

Venus morning star

Venus and the Morning Star

 

In the Greek system of epicycles, Venus rotates in a circle, the centre of which revolves around the Earth; this epicycle centre remains aligned with the Earth and the Sun. Ptolemy explained that this was the reason why Venus never moves very far from the Sun

venus ptolemy model

Venus in Ptolemy's model

 

Copernicus explains it in a simpler way by making Venus an inferior planet, closer to the Sun than the Earth.

venus copernicus model

Copernicus model

 

In autumn 1610, Galileo observed the phases of Venus through his telescope. These observations are incompatible with the Ptolemaic system. The phases can be explained simply in Copernicus’s heliocentric model and in Tycho Brahe’s model in which the Sun moved around the Earth and other planets around the Sun.

venus galileo

The phases of Venus drawn by Galileo

 

venus flammarion

The phases of Venus explained by Flammarion

 

There is virtually no visible detail  when Venus is observed through a telescope. For a long time, Venus was believed to be Earth’s twin on which life might have developed.

venus rudaux

The surface of Venus as it was imagined less than a century ago (drawing Lucien Rudaux).

 

 

In 1957, an amateur astronomer observing Venus in ultraviolet found out that the planet rotates in 4 days. This is actually the period of rotation of the atmosphere. In 1962, a radar observation showed that the planet revolves around its axis in 243 days in a retrograde direction.

Venus was explored by spacecraft in 1962 (overview by Mariner 2). Since 1965, several Venera probes have entered Venus’s atmosphere and were able to photograph the surface. The Magellan probe mapped the terrain in the 90's and Venus Express is currently in orbit around the planet.

At the present time, we know that the surface temperature is over 450 °C and the atmosphere, which is mainly composed of carbon dioxide, generates a significant greenhouse effect.

 

venus magellan

The topography of Venus reconstructed from the data of the Magellan probe

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