27th December:Diameter of Venus measured

The planet Venus has always been visible in the night sky, so was not discovered like the outer planets - but on this date in 1722 James Bradley used what is the longest ever recorded telescope to measure the diameter of Venus. The telescope measured 212 feet and was difficult to use. 10 facts about Venus:

Radar image of Venus, by NASA

1. Its day is longer than its year. It orbits the Sun every 224.7 Earth days, but it takes 243 days for the planet to rotate. It rotates slower than any other planet in the solar system.
2. It is one of the brightest objects in the sky as seen from Earth. Only the sun and Moon are brighter. It can get so bright that it would cast shadows on Earth, and would be visible even in bright daylight.
3. It's always cloudy on Venus. The whole planet is covered in clouds made of sulphuric acid which never clear, so it would not be possible to see Earth or the Sun from the surface. The winds on Venus carry the clouds on a complete trip around the planet every four Earth days. It rains sulphuric acid, but the rain evaporates before it hits the ground. The clouds also produce Lightning. The clouds make studying the surface of Venus quite difficult. The surface cannot be observed with visible light, although scientists have managed to get an idea of what the surface looks like using radar.
4. It's also very hot. Even though it's not the closest planet to the sun (Mercury is) it is the hottest planet in the solar system. The temperature is around 462 °C on the surface, hotter than the temperature required to sterilise things. The clouds are to blame for this along with the carbon dioxide rich (96%) atmosphere. Together they create the most extreme greenhouse effect in the solar system.
5. Venus is one of just two of the planets not to have a moon (the other is Mercury) and one of only two to rotate clockwise instead of anti-clockwise (the other being Uranus).
6. Using radar, scientists have managed to study surface features on Venus. They found that it doesn't have impact craters less than one and a quarter miles across, because small asteroids would be crushed to powder by the high atmospheric pressure (92 times that of Earth). Most of the surface is made up of volcanic plains but it has two higher masses, which, if Venus had oceans, would be continents. The northern continent is called Ishtar Terra, after Ishtar, the Babylonian goddess of love, and is about the size of Australia. The southern continent is called Aphrodite Terra, after the Greek goddess of love, and is the larger of the two highland regions at roughly the size of South America. Most surface features are named after women, both mythological and historical. One exception is the highest mountain on Venus, Maxwell Montes, named after James Clerk Maxwell.
7. Venus has been observed by astronomers since ancient times. Because of the nature of the orbits of Earth and Venus, Venus is sometimes visible in the evening and sometimes in the morning, so many of those ancient astronomers assumed they were looking at two different objects and gave it two names, Phosphorous and Hesperus. By 1581 BCE the ancient Babylonians had figured out these two were actually the same thing, and they called it the "bright queen of the sky". The Chinese called it Tai-pe or “the beautiful white one,” the Egyptians called it Bonou for “bird,” and the Chaldeans named it the “bright torch of heaven.”
8. It is now thought that the UFO that former US President Jimmy Carter claimed to have seen in 1969 was actually Venus.
9. The day of the week, Friday, derives from the Anglo Saxon name for the goddess Venus, Friga. Many other languages have named the last day of the working week after Venus as well, for example, vendredi in French, venerdì in Italian, viernes in Spanish.
10. The astrological symbol for Venus is a circle with a cross underneath. The same symbol is used in biology for the female sex, and in alchemy for the element copper (because copper was used for mirrors in ancient times and so it stands for the mirror of the goddess). The same symbol is sometimes used to represent Friday.