Tuesday, September 22, 2009

Solar System - Venus

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Things you don't know about the Solar System

I've always found space fascinating, and among my first books was a book about astronomy. It was just a small, general guide that had a number of interesting facts about the solar system and the stars and galaxies. This was 1980 or before, and we've made a LOT of discoveries since then, and I've kept up on it, partly thanks to Ars Technica, the Science Channel, and NASA.

I'm going to present a few curious things to you about what surrounds you that I'll bet you don't know. It's time to discover the hottest planet: Venus.

Known in ancient times as both the Morning Star and the Evening Star, Venus is one of the brightest objects in the sky. When Galileo turned his telescope upon it, he discovered that it went through phases, just like the Moon. It does this because it's closer to the Sun than we are - Mercury also goes through phases, but the outer planets do not.

Better telescopes revealed that Venus was about the same size as Earth, and that it was covered in clouds. It gained the name of Earth's Twin, or even Sister Planet, because of this. It was believed for a long time that with it being of similar size and with clouds that it was probably like Earth, only warmer. When space probes finally reached it, they discovered it was just about the worst place you could be! The temperature was over 800 degrees - hotter than Mercury even though it's twice as far away from the Sun! - and the atmosphere was crushing - 90 times the pressure of Earth's atmosphere - and it was mostly carbon dioxide, plus the winds were constantly howling at supersonic speeds and the clouds were too thick for much light to get to the surface.

It wasn't until we started turning our radars on the planet that we made an interesting discovery: Venus rotates backwards! Very slowly! They also discovered something else: Venus always points the same face at Earth.

Okay, that's not precisely true; here’s a more accurate statement: When Venus is closest to the Earth, it always points the same face at Earth. Because Venus is so covered in clouds that we can’t ever see the surface, except by bouncing radar signals off it, we didn’t know this until fairly recently.

Some of you may be aware that Venus rotates “backwards”, or “retrograde”. The Earth and most other solar-system bodies, when viewed from above the North Pole, spin counter-clockwise, but Venus spins clockwise instead. The Sun, if it was visible from Venus’ surface, would go from west to east.
Venus needs 225 Earth-days (about 7.5 months) to revolve around the Sun, and 243 Earth-days (usually listed as -243 days to denote that it rotates backwards) (about 8 months) to rotate 360 degrees. Its “day” is a little longer than its “year”.

Because it takes Venus 2/3 of an Earth-year to rotate, and about that long for Venus to go around the Sun, Venus comes closest to Earth in the same part of the sky every 2 Earth-years. In this time, Venus has gone around the Sun 3 times and also had three full “days”. The same side of Venus is always facing toward Earth when the two approach!

Future study of the planet is likely to reveal that this is not a coincidence, but rather that there is probably a concentration of mass on Venus that Earth “grabs onto”, in much the same way as the near-side of the Moon is heavier than the far side. Over billions of years, Earth’s gravity grabbed hold of these mass concentrations and caused both Venus and the Moon to always face this way on a regular basis. Chances are good that in its past, Venus rotated much like Earth does, then got hit by something big enough to cause it to slow down enough for Earth to grab hold of it and create this interesting 3-to-2 resonance.

I'm going to tell you one more interesting thing about Venus that you don't know: It's possible to live there without terraforming it. How? I'm glad you asked!

You know that Earth's atmosphere is about 100 miles thick, right? And that the higher you go, the thinner the air is, right? The same is true of other planets. Even though the atmospheric pressure on the surface of Venus is 90 times that of Earth, a few dozen miles above that there is a point where it's a lot closer to Earth-normal pressure. By living in what amounts to giant balloons, we could build floating habitats - not much different from living in ships, which we do all the time here on Earth. The conditions in this band are a lot less hostile. The temperatures are better, and the clouds and storms are at a lower level, so it's calmer too. Plus, it's a lot easier to gather sunlight! It might even rain real water up there!

Okay, that's all I've got from Venus for you. Later!

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Further reading to whet your appetite for knowledge:
Solar System - Earth
Solar System - Mercury
To Your Health - Part 2

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1 comment:

  1. Bonus fact (forgive today's date): Many Equatorial civilizations, who don't have seasons like the rest of us do, used Venus to denote the passage of years. I just found this out yesterday.

    ReplyDelete

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