Uranus on July 29, 2009

Uranus is a gas giant planet about the size of Neptune and four times larger than Earth. Its gas composition is mostly hydrogen and helium with small amounts of other gases. A telescope view will not reveal any surface features because a thick, high altitude haze layer hides most of the cloud features below. Even most images taken by the Voyager space probe showed Uranus as a featureless globe. The planet's axis of rotation is tipped almost parallel to the plane of its orbit. This means that at certain points in its orbit, one of the poles is pointed in the direction of the Sun, the other half of the planet remains in constant darkness. Because it takes the planet 84 years to complete one orbit, such a dark season can last for well over 20 years. It is believed that sometime in the past, Uranus was hit by a large body that almost destroyed the planet. The tilted rotational axis and a ring system of left-over debris circling the planet may be evidence of that cataclysmic event.

Uranus is one of three planets in the solar system that rotates backwards. The planet is 2,870,990,000 kilometers from the Sun, and has a diameter of 51,118 km. Uranus completes one rotation on its axis every 17.9 hours. Although Uranus has 14-1/2 times the mass of the Earth, if you could stand on Uranus, you would weigh only 79 percent of your weight on Earth because of the planet's low density. Uranus has at least 21 moons.

All of the planets from Mercury out to Saturn were known to the ancients, because Mercury, Venus, Mars, Jupiter, and Saturn are all easily visible to the naked eye. Uranus was the first planet discovered in modern times. William Herschel is credited with the discovery in 1781. He discovered two of its moons a few years later. Thereafter, Neptune was discovered after the motion of Uranus indicated that another then-unknown planet seemed to be perturbing the orbit of Uranus.

This image was taken from my back yard in Scottsdale, Arizona, using a Takahashi FCT-150 telescope with a 4x PowerMate, achieving an effective focal ratio of approximately f28. An SBIG ST-8XE CCD and a CFW-8 color filter wheel were used to capture the image.

Constellation: Pisces
RA: 23h 47m 44s Dec: -02d 11' 09"
July 29, 2009
Image by Sid Leach
Scottsdale, Arizona

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