The planet Uranus has always been an oddball. It lies on its side, so it rolls around the Sun like a giant bowling ball. Its magnetic field is tilted and offset more than any other planet’s.
And for the past four decades, it’s seemed that the planet radiated less energy into space than it receives from the Sun. The solar system’s other giant planets all radiate at least twice as much energy as they receive – mainly in the form of heat left over from their formation.
But two recent studies have changed that story – at least a little.
Most of the earlier estimates were based on observations by Voyager 2, which flew past the planet in 1986. But the new studies found that Voyager might have scanned Uranus at the wrong time. The Sun was especially active then, skewing the readings.
The studies combined decades of observations by telescopes on the ground and in space. Researchers then used computer models to analyze the results.
They found that Uranus emits up to 15 percent more energy than it gets from the Sun. But that’s still a lot less than the other giants. So Uranus is still an oddball – just not quite as odd as it seemed.
Uranus is at its best this week. It’s opposite the Sun, so it’s in view all night. It’s closest to us for the year as well, so it shines at its brightest. Even so, you need binoculars to see it. It’s in the east in early evening, to the lower right of the Pleiades star cluster.
Script by Damond Benningfield
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Uranus Opposition II
If you suffer from seasonal affective disorder during the dark winter months, then stay away from the poles of Uranus. The giant planet is tilted on its side. So during each 84-year-long orbit around the Sun, the polar regions have 42 years of daylight followed by 42 years of darkness – a looong time to feel sad.
Planetary scientists have been watching the slow change of seasons for two decades with Hubble Space Telescope. At visible wavelengths, Uranus looks like an almost-featureless ball – faint bands of clouds are about the only details. A smattering of methane in the atmosphere absorbs red light, giving the planet a pale green color.
But Hubble’s instruments split the light into its individual wavelengths. It also can see into the infrared, which isn’t visible to the eye. That reveals more details, providing a better picture of what’s going on.
Among other things, it’s revealed that there’s not much methane at the poles, regardless of the season. On the other hand, as the north pole warmed up during spring, it got hazier. At the same time, the haze thinned out over the south pole. Scientists are studying those results to learn more about the planet’s atmosphere and the slow march of its seasons.
Uranus is low in the east in early evening, to the lower right of the Pleiades star cluster. Through binoculars, it looks like a star with just a hint of color.
More about Uranus tomorrow.
Script by Damond Benningfield
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Uranus at Opposition
Uranus is the seventh planet of the solar system, so it’s a long way from both the Sun and Earth. Right now, it’s about 1.7 billion miles away. At that distance, under especially dark skies it’s barely bright enough to see with the eye alone. It’s easy to pick out with binoculars, though.
This is an especially good week to look for the planet because it reaches opposition, when it lines up opposite the Sun. It rises around sunset and is in view all night. And it shines brightest for the entire year. In early evening, it’s close to the lower right of another good binocular target, the Pleiades star cluster.
Even though Uranus is sometimes visible to the eye alone, it’s so faint that no one realized it was planet for a long time. Every astronomer who saw Uranus logged it as a star, missing out on a chance at immortality.
It was officially discovered as a planet by British astronomer William Herschel, in 1781. But even he was fooled by it for a while. When he first saw it, he thought it was a comet. But calculations of its orbit showed that the object was much too far away to be a comet – it had to be a planet, and a big one.
Herschel wanted to call it George’s Star after his patron, King George III. Astronomers outside Britain weren’t crazy about that. So almost 70 years later, they finally named it for a Greek god of the sky: Uranus.
More about Uranus tomorrow.
Script by Damond Benningfield
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Moon and Venus
A barely-there crescent Moon teams up with the disappearing “morning star” in tomorrow’s dawn twilight. But there’s not much time to look for them.
The Moon will cross between Earth and the Sun in a couple of days. It’ll be lost in the Sun’s glare. It will return to view, in the evening sky, by Friday or Saturday.
Venus is getting ready to disappear in the dawn twilight as well. It will cross behind the Sun on January 6th. It’s a slower passage, so the planet will be hidden in the Sun’s glare for about three months. It’ll emerge as the “evening star” in February.
Most cultures figured out that the morning and evening star were actually the same object thousands of years ago. Even so, they had different names for the morning and evening appearances. In ancient Greece, morning Venus was named for the god Phosphorus. In Rome, he was Lucifer. Both names mean “bringer of light” – the god lit the dawn sky with a torch.
Venus passes behind the Sun every 584 days – a bit more than 19 months. Before and after it disappears, it’s almost full. So if you look at Venus with a telescope now, it’ll be almost fully lit up – like a negative image of the “fingernail” crescent Moon.
Look for Venus and the Moon quite low in the eastern sky beginning about 45 minutes before sunrise. Because of the timing and the viewing angle, they’ll be a little easier to spot from the southeastern corner of the country.
Script by Damond Benningfield
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Moon and Spica
If you ever warp over to another star, it would help to know its distance. Say, for example, you wanted to visit Spica, the brightest star of Virgo, which is quite close to the Moon at dawn tomorrow. The system is worth visiting because it consists of two giant stars. They’re so close together that their shapes are distorted, so they look like eggs.
The best measurement we have says that Spica is 250 light-years away. But there’s a margin of error of about `four percent. So you could undershoot or overshoot the system by 10 light-years.
The distances of most stars are measured with a technique called parallax. Astronomers plot a star’s position at six-month intervals, when Earth is on opposite sides of the Sun. That can produce a tiny shift in the star’s position against the background of more-distant objects. The bigger the shift, the closer the star.
But the stars are so far away that the shift is tiny – like the size of a dime seen from miles away – or hundreds of miles. And Earth’s atmosphere blurs the view, so the stars look like fuzzy blobs instead of sharp points.
So the most accurate measurements have been made from space. Spica’s distance was measured by Hipparchos, a European space telescope. An even more accurate satellite, Gaia, measured the distances to more than a billion stars – but not Spica. The star was too bright for its detectors – leaving a big margin of error for this impressive system.
Script by Damond Benningfield
USA