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The Planet Venus

© Copyright 2000, Jim Loy

Here are two pictures of Venus, the one on the left is from NASA (Galileo spacecraft), the one on the right is from Broderbund's ClickArt. When I was young, Venus was considered likely to have life on it. It is just a little smaller than earth. It is in what I call the Momma Bear zone, not too hot (like Mercury) and not too cold (like the outer planets). And it is covered with clouds, much more so than Earth is. Just think of all the water on Venus. Well, Venus is now known to be hot and dry as a bone. It's atmosphere is mostly carbon dioxide, a greenhouse gas. That is what keeps it hot. Light from the sun enters the atmosphere but does not readily escape into space. Temperatures of 870 degrees Fahrenheit have been measured. In the upper atmosphere, sulphuric acid has even been detected. There is probably no life on Venus.

Venus rotates very slowly (once every 243 earth days) in the direction opposite to most of the other planets (and opposite to the motion of all of the planets around the sun). This opposite rotation is called retrograde. This is something of a surprise, because the clouds that we see are going around the planet in the correct direction, not retrograde. Its solar day is 116 days long.

Radar images have shown craters, lowlands, and mountains (including volcanos). A particularly huge mountain has been named Maxwell.

Venus goes around the sun once every 225 days. It has no measurable magnetic field. It is the brightest object in our night sky, except for the moon. This is because it is relatively close to us, it is larger than some planets, and its clouds reflect light very efficiently. It is sometimes called the morning star or the evening star, depending on when it is seen. I will include a photograph or two, later.

On the right are the phases of Venus (from Broderbund's ClickArt), as seen from Earth. The scale is distorted. These phases can be seen with a small telescope or binoculars.

Here are some data about Venus:

• Distance from the sun:
  • perihelion (closest): 66.8 million miles
  • semi-major axis (mean distance): 0.72333 AU (astronomical units, Earth=1) or 67 million miles
  • aphelion (farthest): 67.7 million miles
• Orbit:
  • Period of revolution around the sun: 224.74 days
  • Orbital eccentricity (circle=0): 0.06773
  • Orbital inclination (tilt): 3.3947 degrees
  • Velocity: 21.76 miles per second
• Rotation:
  • Synodic (solar) day -116.75 days
  • Siderial day: -243.018 days
  • Rotational inclination (tilt): 177.33 degrees (rotation is retrograde, so the axis point south with respect to the earth)
• Mass (Earth=1): 0.8151
• Mean radius: 6051km (3761 miles)
• Mean density (Earth=1): 0.943 (5.20 gm/cm)
• Gravity at surface (Earth=1): 0.91
• Mean Temperature at surface: 870 degrees Fahrenheit (temperature varies little from day to night)
• Moons: 0

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