Star date: 03:08:99

Venus: Our (not so) Sister Planet

Venus has been called Earths sister planet. In some ways, this is the case. In other ways, Venus is more like Hell than Earth.

Venus is almost the same size as the Earth, and has nearly the same mass. But the atmosphere of Venus is almost all carbon dioxide and has pressures greater than 90 times that of the Earth. This is about 1/10 as dense as water. If that were not enough, the surface of Venus also experiences rain. That seems like a good idea for such a hot area, until you consider that the rain is composed of sulphuric acid.

Venus is, by far, the brightest object in the night sky other than the Moon. At magnitude -4, Venus is over nine times brighter than the brightest star in the sky, Sirius. Coincidently, Sirius is also in the evening sky this week! Look for it in the south to southeast sky, less than 30 degrees above the horizon. If you hold your clenched fist at arms length (generally speaking), it will span about 10 degrees side to side. So three of these on top of each other would bring you to a point slightly above the altitude of Venus. Sirius will reach its maximum altitude at about 7:20 each evening this week, when it will be nearly due south and 30 degrees above the horizon. It will be the brightest object in this area of the sky.

The surface of Venus has never, until recently, been seen by mankind. When Galileo first turned his telescope toward this world in the opening years of the 17th century, he saw no detail, only clouds. People spent the next 300 years looking at Venus, waiting for a break in the clouds which never came. There are days here in New England when I know what that must feel like from the other side. The technology to see beneath these clouds only arrived after the second world war.

The first peeks beneath the eternal cloud layer of Venus arrived in the form of radar images. These early maps, although there resolution was very poor, were still significant in the fact that they were our first glimpse of this alien world. If the crushing pressures and sulfuric acid rain were not enough to make you cancel your vacation plans for Venus, the surface temperature of 470 c (900 f) should be. Lead, tin, or cadimium would all melt at this temperature. Due to all the carbon dioxide in the atmosphere of Venus, that planet experiences a runaway greenhouse effect. Almost none of the energy which Venus receives from the Sun is reflected back into space, and is transformed into tremendous amounts of heat. A similar process happens when you leave your car in the Sun with the windows rolled up. The energy your car receives from the Sun strikes material in your car (like the seats), and is turned into heat. That heat cannot travel effectively through glass, and is stuck inside the car.

None of the spacecraft which have landed on Venus have operated very long before failing. About an hour at the most. The few images which have been returned from the surface of Venus reveal a desert world, dominated by volcanos. The soil tests done by these robot explorers show that the composition of the surface of Venus is mostly basalts, much like the surface of the Moon. An interesting aspect of Venus is that if it were posiible to survive on the surface of this torrid world, the atmosphere would be so dense that you could easily fly with the simplest of wings. Another advantage to having a winter home on Venus is that the temperatures are so hot, that many of the rocks on Venus are partly molten, and seem to sway in the powerful winds.

So when you are viewing Venus this week in the west/southwestern sky (it's the BRIGHT one!) early in the evening (it sets at 8:30), think of strapping on wings and flying over a molten, volcanic world.

Clear skies, and good viewing.

"Understanding is joyous" - Carl Sagan

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