Hunting Uranus, the Solar System’s Azure Ice Giant

This image shows a full, sunlit hemisphere of Uranus during NASA’s Voyager 2 spacecraft flyby in 1986. Credit: NASA

Amateur astronomers the world over enjoy regular views of Venus, Mars, Jupiter, Saturn and even elusive Mercury. The outer solar system planets Uranus and Neptune, however, are often overlooked.

Certainly they are fainter, as they are further away, so there is much less detail to be seen. That said, they are worthy targets and should be seen as a challenge and not avoided.

My personal interest in Uranus, which can be seen to the west in evening skies through December and January, started when I decided to have a bash at imaging it. To my surprise, it was easy enough to find and with a CCD plugged into the back of my telescope, easily revealed the planetary disk and four of its moons.

Uranus was discovered when 18th Century British astronomer William Herschel was engaged in the systematic study of stars in the night sky to identify double stars. For two years he studied the night sky almost every night and on March 13, 1781, he noticed a star in Taurus that seemed to appear a little different to the others.

As with all good astronomical observations Herschel studied the same object few nights later and noticed it had moved with respect to the background stars proving to Herschel that it was a new solar system object. He originally suspected it was a comet but later, its planetary nature was unveiled. Clearly a supporter of the monarchy, Herschel wanted to name the new planet Georgium Sidius after King George III but it was officially named Uranus, a Latinized version of the Greek god of the sky, Ourano.

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The planet Herschel discovered increased the size of the known solar system to about 5.6 billion kilometers. Future observations revealed a world just over 50 thousand kilometers in diameter and gaseous in nature. Due to the presence of ices in its atmosphere such as ammonia and methane, Uranus is referred to as an “ice giant,” differentiating itself from Jupiter and Saturn. The presence of methane leads to the absorption of red light and the reflection of blue light giving Uranus is stunning blue color.

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