Venus

Venus
	Image of Venus, as captured by MESSENGER. A cloud layer permanently obscures the surface.
Designations
Pronunciation	/ˈviːnəs/ ( listen)
Adjectives	Venusian or (rarely) Cytherean, Venerean
Orbital characteristics
	Epoch J2000
Aphelion	0.728213 AU; 108,939,000 km;
Perihelion	0.718440 AU; 107,477,000 km;
Semi-major axis	0.723332 AU; 108,208,000 km;
Eccentricity	0.006772
Orbital period	224.701 d; 0.615198 yr; 1.92 Venus solar day;
Synodic period	583.92 days
Average orbital speed	35.02 km/s
Mean anomaly	50.115°
Inclination	3.39458° to ecliptic; 3.86° to Sun's equator; 2.19° to invariable plane;
Longitude of ascending node	76.680°
Argument of perihelion	54.884°
Satellites	None
Physical characteristics
Mean radius	6,051.8±1.0 km; 0.9499 Earths;
Flattening	0
Surface area	4.6023×108 km2; 0.902 Earths;
Volume	9.2843×1011 km3; 0.866 Earths;
Mass	4.8675×1024 kg; 0.815 Earths;
Mean density	5.243 g/cm3
Surface gravity	8.87 m/s2; 0.904 g;
Escape velocity	10.36 km/s (6.44 mi/s)
Sidereal rotation period	−243.025 d (retrograde)
Equatorial rotation velocity	6.52 km/h (1.81 m/s)
Axial tilt	2.64° (for retrograde rotation); 177.36° (to orbit)
North pole right ascension	18h 11m 2s; 272.76°;
North pole declination	67.16°
Albedo	0.689 (geometric); 0.76 (Bond);
Apparent magnitude	−4.92 to −2.98
Angular diameter	9.7″–66.0″
Atmosphere
Surface pressure	92 bar (9.2 MPa)
Composition by volume	96.5% carbon dioxide; 3.5% nitrogen; 0.015% sulfur dioxide; 0.007% argon; 0.002% water vapour; 0.0017% carbon monoxide; 0.0012% helium; 0.0007% neon; trace carbonyl sulfide; trace hydrogen chloride; trace hydrogen fluoride;
	↑ 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°. ;

Venus is the second planet from the Sun.^[2] Venus is the only planet in the Solar System that has a day longer than a year. The year length of Venus is 225 Earth days. The day length of Venus is 243 Earth days.^[2]

Overview

Venus is a terrestrial planet because it has a solid, rocky surface like other planets in the inner Solar System. Astronomers have known Venus for thousands of years. The ancient Romans named it after their goddess Venus, goddess of love and beauty.^[2]

Venus is the brightest thing in the night sky except for the Moon. It is sometimes called the morning star or the evening star as at some elongations it is easily seen just before the Sun comes up in the morning. At other times, it can be seen just after the sun goes down in the evening. Venus comes closer to the Earth than any other planet does.

Composition

Venus is sometimes called the sister planet of Earth as they are quite similar in size and gravity. In other ways the planets are very different. Venus' atmosphere is mostly carbon dioxide (CO₂) with clouds of sulphuric acid (H₂SO₄).^[3] H₂SO₄ is a chemical that is poisonous to life. For this it is sometimes known as the Earth's "evil twin".^[4]^[5]

The thick atmosphere makes it hard to see the surface. Until the late twentieth century many thought there might be life there. The pressure on Venus' surface is 92 times that of Earth. Venus is one of only two planets in the Solar System (the other being Mercury) that has no moons. Venus spins very slowly on its axis and it spins in the opposite direction to the other planets.

Physical properties

Radar view of the surface of Venus (Magellan spacecraft)

Venus is a terrestrial planet so, like the Earth, its surface is made of rock. Venus is much hotter than Earth. All the carbon dioxide in the atmosphere acts like a blanket, trapping heat from the Sun. This effect is called the greenhouse effect and it is very strong on Venus. This makes the surface of Venus the hottest of any planet's surface in the Solar System with an estimated average temperature of 480 °C (896.0 °F).^[6]^[7] This is hot enough to melt lead or zinc.

Geography

Venus has no oceans because it is much too hot for water. Venus' surface is a dry desert. Because of the clouds, only radar can map the surface. It is about 80% smooth, rocky plains, made mostly of basalt. Two higher areas called continents make up the north and south of the planet. The north is called Ishtar Terra and the south is called Aphrodite Terra. They are named after the Babylonian and Greek goddesses of love.^[8]

The surface of Venus looks like it has been shaped by volcanic activity. Venus has a lot of volcanoes.^[9] The surface of Venus is estimated to be 300–600 million years old.^[9]^[10]

Unlike Earth or Mars, Venus does not have defined highlands or lowlands, and it does not have tectonic plates.

Atmosphere

Venus' atmosphere is mostly carbon dioxide and nitrogen gas with clouds of sulphuric acid. Because the atmosphere is so thick or dense the pressure is very high. The pressure is 92 times the pressure on Earth, enough to crush many things.

It is impossible to see the planet's surface from space as the thick cloud layer reflects 60% of the light that hits it. The only way scientists are able to see it is by using infrared and ultraviolet cameras and radar.

Scientists believe that billions of years ago, the atmosphere of Venus could have been like Earth's atmosphere. There may have been lots of water on the surface of Venus. But after 600 million to several billion years, the evaporation of the water put greenhouse gases into its atmosphere.^[11]

Magnetic field

In 1967, Venera 4 found that the magnetic field of Venus was much weaker than that of Earth. This magnetic field is induced by an interaction between the ionosphere and the solar wind. Venus' magnetosphere is not strong enough to protect the atmosphere from cosmic rays.^[12]

Transit of Venus

Main page: Transit of Venus

Venus can sometimes be seen passing between the Sun and Earth. Venus looks like a black dot when seen through a special telescope. These passages are called "transits". These "transits" happen in pairs eight years apart. Then it is more than a hundred years to the next pair.

Orbit and rotation

Main page: Orbit of Venus

Orbit of Venus compared to the orbit of the Earth

Venus orbits the Sun at an average distance of about 108 million km (68~ million mi). It completes an orbit every 224.7 days.^[13] The rotation of Venus is slow. A Venusian sidereal day is longer than a Venusian year.

List of satellites sent to Venus

Many man-made satellites have been sent to Venus to study it. They are:

Mariner

{{#section-h:List of satellites sent to Venus|Mariner Satellites}}

Venera

{{#section-h:List of satellites sent to Venus|Venera Satellites}}

Venus Media

Radar mosaic of two pancake domes in Venus's Eistla region—both 65 km (40 mi) wide and less than 1 km (0.62 mi) high
Impact craters on the surface of Venus (false-colour, 3D projection image reconstructed from radar data)
The differentiated structure of Venus
Venus interacts with the solar wind. Components of the induced magnetosphere are shown.
Cloud structure of the Venusian atmosphere, made visible through ultraviolet imaging
Atmospheric profile by altitude (left scale): cloud layers, temperature change (VIRA thick line and bottom scale), pressure change (right scale) and wind speed (PV dotted lines and top scale)
Venus is the second planet from the Sun, making a full orbit in about 224 days.
Venus and its rotation in respect to its revolution
Earth is positioned at the centre of the diagram, and the curve represents the direction and distance of Venus as a function of time.