Venus is the second planet from the Sun and is named after the Roman goddess of love and beauty. As the brightest natural object in Earth's night sky after the Moon, Venus can cast shadows and can be visible to the naked eye in broad daylight. Venus's orbit is smaller than that of Earth, but its maximal elongation is 47°; thus, at latitudes with a day-night cycle, it is most readily visible for up to a few hours following the start of sunset or before sunrise. Unlike Mercury, which can only be observed during twilight, Venus can be seen in a completely dark sky. Venus orbits the Sun every 224.7 Earth days, but rotates around its axis in 243 Earth days. Consequently, it takes longer to rotate about its axis than any other planet in the Solar System, and does so in the opposite direction to all but Uranus. This means that the Sun rises from its western horizon and sets in its east. This retrograde rotation creates a synodic day of only 117 Earth days. Venus does not have any moons, a distinction it shares only with Mercury among the planets in the Solar System.
|Adjectives||Venusian / - /,, rarely Cytherean // or Venerean / Venerian //|
Average orbital speed
|10.36 km/s (6.44 mi/s)|
|−116.75 d (retrograde)
1 Venus solar day
|−243.0226 d (retrograde)|
Equatorial rotation velocity
|6.52 km/h (1.81 m/s)|
|2.64° (for retrograde rotation)|
177.36° (to orbit)
North pole right ascension
North pole declination
|Surface absorbed dose rate||2.1×10−6 μGy/h|
|Surface equivalent dose rate||2.2×10−6 μSv/h|
0.092–22 μSv/h at the habitable zone
|−4.92 to −2.98|
|93 bar (9.3 MPa)|
|Composition by volume|
The third smallest planet in the Solar System, Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to the Sun, and bulk composition. It is radically different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet's surface is about 92 times the sea level pressure of Earth, or roughly the pressure at 900 m (3,000 ft) underwater on Earth. Even though Mercury is closer to the Sun, Venus has the hottest surface of any planet in the Solar System, with a mean temperature of 737 K (464 °C; 867 °F). Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from Earth in light. It may have had water oceans in the past, but after these evaporated the temperature rose under a runaway greenhouse effect. The water has probably photodissociated, and the free hydrogen has been swept into interplanetary space by the solar wind because of the lack of a planetary magnetic field. Because of the lethal surface conditions, the planet is sometimes referred to as Earth's "evil twin".
As one of the brightest objects in the sky, Venus has been a major fixture in human culture for as long as records have existed. It has been made sacred to gods of many cultures and has been a prime inspiration for writers and poets as the "morning star" and "evening star". Venus was the first planet to have its motions plotted across the sky, as early as the second millennium BCE.
Its proximity to Earth has made Venus a prime target for early interplanetary exploration. It was the first planet beyond Earth visited by a spacecraft (Venera 1 in 1961) and the first to be successfully landed on (by Venera 7 in 1970). The planet's thick clouds render observation of its surface impossible in the visible spectrum, and the first detailed maps did not emerge until the arrival of the Magellan orbiter in 1991. Plans have been proposed for rovers or more complex missions, but they are hindered by Venus's hostile surface conditions. The possibility of life on Venus has long been a topic of speculation; in recent years, the topic has received active research.