Venus

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

Orbit and Rotation

• Averages 67.3 million miles from the Sun. With the most nearly circular orbit, this distance varies only half a million miles on either side.
• Revolves around the Sun in 225 days, rotates, BACKWARDS, in 243 days.

Atmosphere of Venus

• Has a dense carbon-dioxide atmosphere, with trace amounts of carbon monoxide, hydrogen chloride, and hydrogen fluoride.
• Covered with a thick layer of clouds which are made up mostly of sulfuric acid droplets.
• The atmosphere of Venus traps solar heat and has created a "runaway greenhouse effect."
• Surface temperatures average 400 degrees C or about 900 degrees F.
• Pressures at the Surface are about 90 atmospheres.

The Surface of Venus

• Close-up images of the surface show that some form of deposition and erosion occurs.
• Thanks to the Pioneer, Magellan and Venera radar orbiters, the surface of Venus is now mapped more completely and uniformly than the Earth.
• Radar mapping from earth and from orbit indicate large valleys and plateaus, probably craters, and large volcanic complexes. The plateaus on Venus are not continents as on the Earth, and overall Venus is much smoother than Earth.

Topography of Venus

Geography of Venus

• Venus has numerous volcanoes. Some scientists think the sulfuric acid in Venus' atmosphere may be of volcanic origin.
• Venus seems to have had a planetwide volcanic episode about 600 million years ago that covered much of its surface and covered its earlier craters.

  Venus and Earth

  • Venus is nearly a twin to the earth in terms of size and density.
  • Venus is smoother than the Earth and does not show evidence for two kinds of crust as does Earth.
  • Although volcanically and tectonically active, Venus lacks plate tectonics.
  • Probably has a core but lacks a magnetic field.

  Venus and Earth Near Resonances

  • 8 Earth years = 2922.048 days
  • 13 Venus Years = 2921.035 days
  • 5 Venus-Earth Synodic Periods = 2919.415 days
  • 12 Venus Rotations = 2916.224 days
  • Synodic period of Venus' rotation with respect to Earth = 145.927 days. 4 of these periods = 583.7 days. This is very nearly the synodic period of Venus with respect to earth. 20 Venus rotation/earth synodic periods = 2918.551 days.

  So Venus' rotation and orbital motion repeat the same configurations with respect to earth every 2920 days. Almost. But they are not perfect. For example, Venus transited the Sun on June 8, 2004 and did so again on June 4, 2012. But since the resonance isn't exact, the inferior conjunction date drifts and there will be no transit in 2020 because Venus will be too far from its node at inferior conjunction.

  Dan Brown blathers at length about these cycles in The Da Vinci Code, claiming that they are perfect. But they're not. However, they are close enough to make one wonder if there was a resonance in the past or perhaps will be one in the future.

  Venus' Rotation

  

  The animation above follows Venus and Earth through one synodic period. Note that because of its retrograde rotation, it takes less than 243 days for Venus to rotate with respect to the Sun. Also note that Venus rotates four times with respect to the earth during a synodic period (i.e., the red reference line points toward Earth four times).

  As Seen From Earth

  • Venus is the brightest (Mag -4) and nearest (as little as 26,000,000 miles) planet to Earth.
  • It can get up to 45 degrees from the sun and rise or set up to 3-1/2 hours before or after the Sun.

  References

  • Gerald Schubert and Curt Covey, 1981, The Atmosphere of Venus. Scientific American, vol. 245, no. 1, pp. 66-75
  • Gordon H. Pettengill, Donald B. Campbell and Harold Masursky, 1980, The Surface of Venus. Scientific American, vol. 243, no. 2, pp. 54-65
  • Ronald G. Prinn, 1985, The Volcanoes and Clouds of Venus. Scientific American, vol. 242, no. 3, pp. 46-53
  • Powell, Corey S., Three faces of Venus (radar images based on Magellan probe data) Scientific American, v268 p26-7 May 1993
  • Powell, Corey S., Venus revealed: stunning maps strip the clouds from a restless planet (Magellan radar images) Scientific American, v266 p16-17 January 1992
  • Saunders, R. Stephen, The surface of Venus (radar mapping by Magellan spacecraft) Scientific American, v263 p60-5 December 1990

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  Created 20 May 1997, Last Update 12 January 2020