Venus

Venus
	A real-colour image taken by Mariner 10 processed from two filters, the surface is obscured by thick sulfuric acid clouds
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.^[3] 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.^[3]

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.^[3]

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.

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 (air) is mostly carbon dioxide with clouds of sulphuric acid.^[4] Sulphuric acid is a chemical that is poisonous to life. For this it is sometimes known as the Earth's "evil twin".^[5]^[6]

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.

↑ Lakdawalla, Emily better (21 September 2009). "Venus Looks More Boring Than You Think It Does". The Planetary Society. Archived from the original on 6 January 2012. Retrieved 4 December 2011.
↑ "Planets and Pluto: Physical Characteristics". NASA. 5 November 2008. Archived from the original on 7 September 2006. Retrieved 26 August 2015.
↑ ^3.0 ^3.1 ^3.2 "Venus". NASA Solar System Exploration. Archived from the original on 2021-10-19. Retrieved 2021-10-19.
↑ "The Atmosphere of Venus". Archived from the original on 2009-03-02. Retrieved 2008-08-19.
↑ Hall, Shannon (June 5, 2019). "Venus is Earth's evil twin — and space agencies can no longer resist its pull". Nature. Archived from the original on June 5, 2021. Retrieved June 6, 2021.
↑ Greenfieldboyce, Nell (June 2, 2021). "NASA Picks Twin Missions To Visit Venus, Earth's 'Evil Twin'". NPR. Archived from the original on June 5, 2021. Retrieved June 6, 2021.

[3] 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°.

[Lakdawalla2009-1] Lakdawalla, Emily better (21 September 2009). "Venus Looks More Boring Than You Think It Does". The Planetary Society. Archived from the original on 6 January 2012. Retrieved 4 December 2011.

[2] "Planets and Pluto: Physical Characteristics". NASA. 5 November 2008. Archived from the original on 7 September 2006. Retrieved 26 August 2015.

[:2-4] 3.0 ^3.1 ^3.2 "Venus". NASA Solar System Exploration. Archived from the original on 2021-10-19. Retrieved 2021-10-19.

[5] "The Atmosphere of Venus". Archived from the original on 2009-03-02. Retrieved 2008-08-19.

[6] Hall, Shannon (June 5, 2019). "Venus is Earth's evil twin — and space agencies can no longer resist its pull". Nature. Archived from the original on June 5, 2021. Retrieved June 6, 2021.

[7] Greenfieldboyce, Nell (June 2, 2021). "NASA Picks Twin Missions To Visit Venus, Earth's 'Evil Twin'". NPR. Archived from the original on June 5, 2021. Retrieved June 6, 2021.

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