The planet Venus: known for love, rotational contrariness, crushing atmospheres, furnace-like temperatures and acid rain.

Venus is the second closest planet to the Sun and, like Mercury, it has no moon. With a diameter of 12,104 kilometres it is the most similar planet in size to the Earth.

In orbit

Its orbit about the Sun takes 224.7 days with its mean distance from the Sun being almost three-quarters that of the Earth. Highly unusually, the planet rotates in the opposite direction to its orbit in 243 days with respect to the stars (117 days with respect to the Sun, the Venusian day).

A lot like Earth?

Because the size and mass of the planet Venus are close to those of the Earth it was supposed by many that Venus might be Earthlike and might even have life-forms on its surface. The truth is that Venus is very different from the Earth and it is extremely unlikely that there is any possibility that life has formed on Venus.

The atmosphere

On the surface of the planet Venus, the pressure is 90 times that of Earth's. Unlike our atmosphere, which is mainly composed of nitrogen and oxygen, Venus' is made up of 97% carbon dioxide with most of the remainder being nitrogen and argon. One consequence of all that carbon dioxide is that Venus suffers from a severe greenhouse effect and the surface reaches 470°C.

The clouds in the atmosphere of Venus which obscure our view of the surface are not composed of water droplets but are believed to be composed of droplets of sulphuric acid and particles of sulphur – making Venus a far from lovely place for humans to contemplate visiting.

The surface of the planet Venus

The most modern information about the surface comes from the Magellan Venus orbiter. This uses radar to map the surface. It has revealed mountains, valleys, cliffs, craters and huge volcanoes, at least one of which is believed to be active. Active volcanoes are known to exist on only two planets in the solar system, Venus and Earth.

The interior of Venus is believed to be similar to that of the Earth with a metallic core and silicate mantle. Unlike the Earth, Venus has a very small magnetic field apart from that induced by the effect of the solar wind.

UFOs

Venus is best seen in the evening when it is to the east of the Sun and in the morning when it is to the west of the Sun. It is hard to mistake it for any other object as it is so bright. When near the horizon, the ‘twinkling' can give rise to amazing flashing colour effects which are often reported as peculiar objects and even UFOs.

Love

Venus is named after the Roman goddess of love and beauty (Greek Aphrodite).

The transit of Venus

The transit of Venus is a rare astronomical event, when Venus passes directly between the Earth and the Sun, appearing as a small black dot against the Sun’s face. Transits come in pairs, eight years apart. The most recent were in 2004 and 2012 and the next will occur in 2117.

Historically, transits of Venus were used by astronomers to give the first accurate measure of the distance between the Earth and the Sun. To be sure of observing transits of Venus, expeditions were sent around the world in the 18th and 19th centuries. Famously, Captain Cook was sent to Tahiti to observe the transit of 1769, and King George III had Kew Observatory built so that he could personally view the transit.

The Royal Observatory is open daily from 10am

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