Venus

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.[18][19] 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,[20] 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.[21] Venus does not have any moons, a distinction it shares only with Mercury among the planets in the Solar System.[22]

Venus
False colour composite of Venus in visual and ultraviolet wavelengths (from Mariner 10). The surface is completely obscured by clouds.
Designations
Pronunciation/ˈvnəs/ (listen)
AdjectivesVenusian /vɪˈnjziən, -ʒən/,[1] rarely Cytherean /sɪθəˈrən/[2] or Venerean / Venerian /vɪˈnɪəriən/[3]
Orbital characteristics[4][5]
Epoch J2000
Aphelion
  • 0.728213 AU
  • 108,939,000 km
Perihelion
  • 0.718440 AU
  • 107,477,000 km
  • 0.723332 AU
  • 108,208,000 km
Eccentricity0.006772[6]
583.92 days[4]
35.02 km/s
50.115°
Inclination
76.680°[6]
54.884°
SatellitesNone
Physical characteristics
Mean radius
  • 6,051.8±1.0 km[8]
  • 0.9499 Earths
Flattening0[8]
  • 4.6023×108 km2
  • 0.902 Earths
Volume
  • 9.2843×1011 km3
  • 0.857 Earths
Mass
  • 4.8675×1024 kg[9]
  • 0.815 Earths
Mean density
5.243 g/cm3
  • 8.87 m/s2
  • 0.904 g
10.36 km/s (6.44 mi/s)[10]
−116.75 d (retrograde)[11]
1 Venus solar day
−243.0226 d (retrograde)[12]
Equatorial rotation velocity
6.52 km/h (1.81 m/s)
2.64° (for retrograde rotation)
177.36° (to orbit)[4][note 1]
North pole right ascension
  • 18h 11m 2s
  • 272.76°[13]
North pole declination
67.16°
Albedo
Surface temp. min mean max
Kelvin 737 K[4]
Celsius 464 °C
Fahrenheit 867 °F
Surface absorbed dose rate2.1×10−6 μGy/h[16]
Surface equivalent dose rate2.2×10−6 μSv/h
0.092–22 μSv/h at the habitable zone[16]
−4.92 to −2.98[17]
9.7″–66.0″[4]
Atmosphere[4]
Surface pressure
93 bar (9.3 MPa)
92 atm
Composition by volume
  1. Defining the rotation as retrograde, as done by NASA space missions and the USGS, puts Ishtar Terra in the northern hemisphere and makes the axial tilt 2.64°. Following the right-hand rule for prograde rotation puts Ishtar Terra in the southern hemisphere and makes the axial tilt 177.36°.

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,[23][24] but after these evaporated the temperature rose under a runaway greenhouse effect.[25] 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.[26] Because of the lethal surface conditions, the planet is sometimes referred to as Earth's "evil twin".[27]

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.[28]

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.


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