http://www.sina.com.cn 2008年01月23日 11:16
Originally named after the Roman goddess of love, the planet Venus also used to be known as the morning star and the evening star because it shines so brightly that it is visible on Earth even when the Sun is only partially visible in the morning and the evening.
Why does Venus shine so brightly? One reason is certainly because Venus is so close to Earth; it is, in fact, the closest planet to Earth. However, its proximity to Earth is not the only reason that Venus appears to shine so brightly. Another reason that Venus shines so brightly is that it is covered in thick white clouds that reflect sunlight off of them.
For quite some time, all that we have been able to see of Venus is the thick clouds that surround it, and little else was known of the planet itself. Dozens of space probes were sent to Venus in the last part of the twentieth century, and most of them were destroyed before they were able to send back information about Venus’s surface. One probe, however, did manage to transmit some messages before it, too, failed.
From this one partially successful probe, numerous amazing facts about Venus have been learned. The thick clouds that cover Venus, for example, are made of sulfuric acid rather than oxygen, and these thick clouds never part to let any sunshine in at all. Most amazingly, the temperature on Venus is extremely hot, somewhere around 900 degrees Fahrenheit.
It was really surprising to scientists when they found out that Venus was so hot because the clouds around Venus reflect almost all the light from the Sun back into space. The small amount of sunlight that’s able to filter through the clouds doesn’t seem like anywhere near enough light to make the temperature on Venus so high. Instead, because it’s always so cloudy on the surface of Venus, the temperature should be rather cool.
You might think that the temperature on Venus is so hot because Venus is so close to the Sun, but this isn’t really a good explanation for the heat on Venus. The temperature on Venus is even hotter than the temperature on Mercury, which is closer than Venus to the Sun, so the proximity of Venus to the Sun doesn’t explain the high temperature on Venus
Scientists are still not certain why the temperature on Venus is so high, but one possible explanation is Venus’s carbon dioxide atmosphere. The very dense atmosphere on Venus is almost entirely carbon dioxide. This carbon dioxide may create a barrier that traps any heat that gets through beneath it and doesn’t let it escape.