President's Message - Aug 2005

August 2005

Scott Mair

They're big; they're cold; they're gassy and August is the best time this year to look for them. Say hi to Uranus and Neptune. Both planets will be at opposition (with the Earth directly between the planet and the Sun) in August: Neptune on the 7th; Uranus on the 31st. That means they're as about as close as they get to the Earth. Mind you that's still pretty far away: Uranus will be about 2.7 billion kilometers from the Earth; and Neptune 4.35 billion kilometers away.

Uranus was the first planet to be found in the modern era, discovered by William Herschel on March 13, 1781 (all the other planets at that time from Mercury to Saturn had been known from ancient times). Uranus had actually been seen many times before, but ignored as simply another star. Herschel was the first to recognize it as a planet.

You'd think that if you discovered a planet you'd get to name it but, not the case for Herschel. He wanted to call it, George (actually, Georgium Sidus the Georgian Planet). I guess it was too clearly a case of sucking-up (George was the King of England at the time) so most of his friends called it planet Herschel. Apparently though, naming something as important as a planet after the discoverer is just not done in 18th century England. Herschel's second choice was to call the planet Neptune, but that didn't take either. Eventually the community of astronomers agreed on Uranus which just goes to show that planets should never be named by committee - no matter how much 10 year-old boys like saying "your anus".

Something catastrophic seems to have happened to Uranus, because it is the only planet in the solar system that spins on its side as if it was struck by a massive object early in its life, Thanks to the Voyager 2 spacecraft we also know that Uranus (and Neptune, too) has rings like Saturn.

NASA's Solar System Exploration Planets Uranus Overview

NASA's Solar System Exploration Planets Neptune Overview

Neptune has the distinction of being the first planet whose presence was predicted before it was actually discovered. Some weirdness in the way Uranus travels around the Sun suggested that the gravity of an unknown planet was affecting Uranus's orbit. After some clever calculations by French and English astronomers Neptune was discovered by the Galle and d'Arrest on September 23, 1846.

It's only through bad luck that Neptune wasn't discovered by Galileo 233 years earlier. He saw Neptune while observing Jupiter in 1613 and thought it was a star. Although he noticed some movement of the 'star' on subsequent nights it wasn't enough to confirm it as a planet before it was out of his field of view. If the previous days hadn't have been cloudy Galileo would certainly have noticed the relative movement of Neptune and identified it as a planet.

If you want to see Neptune and Uranus for yourself point toward Aquarius for Uranus and Capricorn for Neptune. You'll need binoculars or a telescope and a good star chart, but with a little imagination you might just feel the presence of Herschel and Galileo as track down these elusive planets.

Sky and Telescope - Uranus and Neptune in 2005