Lance Kuester, age 11, of Phoenix, Arizona, for his question:
How does Uranus orbit the sun?
Uranus is a retrograde planet, which has something to do with the way in which it orbits the sun. This hazy, apple green planet is the seventh from the sun and because of its great distance from us, it has been somewhat mysterious. However, in the near future we can expect some close up information. Mariner spacecrafts are scheduled to brush past Uranus on their grand tours of the outer realms of the solar system.
All the planets, including Uranus, travel eastward around their solar orbits. Most of them have direct rotation, which means that they spin toward the east to match their orbital direction. But, Uranus rotates backwards, so to speak, towards the west. This is why it is called a retrograde planet.
Its great oval orbit is the seventh planetary orbit from the sun, between Saturn and faraway Neptune. Its average distance from the sun is 1,785 million miles. But because its orbit is off center, this average distance varies by 166 million miles. Its closest approach to Earth is about 1,700 million miles.
Though Uranus is almost four times wider than Earth, it is barely visible in our skies. It can be seen as a dim dot on very clear nights if we know just where to look. It was discovered about 200 years ago.
The event caused a great stir of excitement and after some debate; it was named for the Greek god of the starry heavens.
We orbit the sun at 18 11 miles per second, but the outer planets orbit more slowly. Uranus pokes along at 4.25 miles per second and takes about 84 earth years. However, a day and night period whizzes by in 10 hours and 49 minutes.
Day and night, of course are related to rotation and the big planet's fast spin may account for the fact that its globe is quite flattened at the poles. There is another remarkable fact about the rotation of Uranus. So far as we know, the rotational axes of all planets are tilted toward the plane of their orbits. The earth leans forward at 23; degrees. Most axes are nearly perpendicular, not far from an angle of 90 degrees.
The axis of Uranus is tilted 93 degrees, which is more than a right angle. It seems to bowl around its orbit, lying on its side. Possibly this peculiar position gives Uranus a backward or retrograde rotational spin.
Though a big planet, Uranus is much smaller than the two giants, Jupiter and Saturn. Its diameter of 29,000 miles makes it almost four times wider than Earth. However, little Earth is 511 times the density of water while the density of Uranus is merely 1.27. The big light¬weight planet spins fast as it dawdles eastward around its huge orbit. And it rolls along lying down, rotating in a retrograde direction towards the west.