Uranus at opposition

¡SkyCaramba! Weekly astronomy blog for the week ending September 28, 2013

Uranus is at opposition on October 3. It will be nearly opposite the sun in the sky, so the planet will rise as the sun sets. You’ll find Uranus on the meridian almost exactly 12 hours after local high noon.

Opposition is often the best time to look at some planets. A planet at opposition is closest to Earth at that time. Uranus will be 19 astronomical units, or earth-sun distances, from us on October 3.

You may be able to spot the faint blue dot with the naked eye. But you’ll need a very dark sky and enough time in the dark to let your eyes adjust to it. Some people can’t see objects that dim without help. It’s okay if you’re one of them. Nearly everyone prefers the telescope or binocular view anyway.

You’ll still need to know exactly where to look to find Uranus with binoculars or a telescope. A planetarium program can be a big help. So can a finder’s guide. In any case, it’s best to look on several nights so you can get used to the arrangement of stars in that part of the sky and detect the planet barely moving among them.

Uranus is a big ball of gas. Most of the gas, about 83%, is believed to be hydrogen. Helium is 15% of it. Methane is 2%. The gas ball also contains very small amounts of water and ammonia. The water and ammonia are frozen.

Astronomers had seen Uranus dozens of times and mistook it for a star before William Herschel recognized that it was different in 1781. Herschel, however, thought he had spotted a comet. He and many other astronomers had to make many observations before he was persuaded that he had discovered a planet.

The axis of Uranus is tilted nearly 98°. That’s so far, it’s easy to think of the planet as not only being on its side but also spinning backwards and upside-down.

Here are some links to help you get the most out of observing Uranus.