Venus

Venus is often called Earth’s twin because it is the closest planet in size to Earth. Scientists estimate the diameter of Venus at about 7,520 miles, making it approximately 400 miles smaller in diameter than Earth.a Although it is called Earth’s twin, the surface conditions of Venus are very different from those on Earth. Scientists believe the planet’s surface is very hot and dry and contains no liquid water, due to extremely high surface temperatures.a Ancient astronomers called Venus both Phosphorous and Hesperus, mistakenly believing that the object visible in the morning and evening were two separate celestial bodies. The planet was later named Venus after the Roman goddess of beauty andlove.f Venus travels around the sun in a nearly circular orbit, with its average distance from the sun varying only slightly throughout the orbit. It takes the planet approximately 225 Earth days to travel completely around the sun, compared to Earth's 365 days.c With its faster orbit around the sun, Venus overtakes Earth every 584 Earth days, changing from an evening star (visible after sunset) to a morning star (visible before sunrise), and then vice versa.a Venus is one of only two planets that rotates on its axis clockwise from east to west. The only other planet to do so is Uranus.a Because Venus rotates very slowly on its axis (taking 243 days to make a complete rotation), a day on Venus is longer than its year.f Venus is the brightest star or planet visible from Earth When seen from Earth, Venus is brighter than any other planet or any star in the sky. At certain times of the year, it is the first planet or star visible in the western sky at night—and at other times, it is the last planet or star visible in the morning.d Venus is constantly covered by thick clouds of sulfuric acid, through which no visible light can penetrate. For this reason, astronomers have been unable to view the planet’s features through optical telescopes. Most of the knowledge about Venus’ surface has been gained through radar images acquired from U.S. and Soviet space probes.c Approximately 65% of Venus’ surface is covered in flat, smooth plains, and the remaining 35% is made up of six mountainous regions. The mountain range Maxwell, which is about seven miles high and 540 miles long, is the highest feature on the planet.a