Author: Fraser Cain

[/caption]
One of the most bizarre weather patterns ever discovered is a hexagon-shaped storm located at Saturn’s northern pole.

The hexagon at Saturn was first seen by NASA’s Voyager 1 and 2 spacecraft when they first visited the planet more than two decades ago. More recently, the Saturn hexagon was imaged in great detail by NASA’s Cassini spacecraft, currently in orbit around Saturn. The Saturn hexagon is exactly that; a hexagon-shaped band of clouds sitting right at Saturn’s north pole. The hexagon is 25,000 km (15,000 miles) across. In fact, you could nearly fit 4 planets the size of Earth in there.

We have a similar feature here on Earth called the polar vortex. But on Earth, the polar vortex winds travel in a circular pattern around the north pole. The Saturn hexagon rotates exactly the same speed as Saturn rotates, and has been since it was first discovered by Voyager more than 25 years ago.

The northern hexagon is dramatically different from Saturn’s southern pole, which has a huge hurricane with a giant eye. Astronomers originally believed that there wasn’t a hexagon at Saturn’s south pole, but new research found one there too.

So why is the hexagon there? Astronomers have no idea. Here’s what Kevin Baines, atmospheric expert and member of Cassini’s visual and infrared mapping spectrometer team at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. had to say, “This is a very strange feature, lying in a precise geometric fashion with six nearly equally straight sides. We’ve never seen anything like this on any other planet. Indeed, Saturn’s thick atmosphere where circularly-shaped waves and convective cells dominate is perhaps the last place you’d expect to see such a six-sided geometric figure, yet there it is.”

We have written many articles about Saturn for Universe Today. Here’s the article where we first announced the updated images of the Saturn hexagon. And here’s an article with images of a hexagon at Saturn’s southern pole.

Want more information on Saturn? Here’s a link to Hubblesite’s News Releases about Saturn, and here’s NASA’s Solar System Exploration Guide.

We have recorded a podcast just about Saturn for Astronomy Cast. Click here and listen to Episode 59: Saturn.

Reference:
NASA

[/caption]
Jupiter is one of the 5 planets visible with the unaided eye, and so it has been known for thousands of years. But the movement of Jupiter and the other planets was a mystery until just a few hundred years ago. Jupiter moves across the sky in a very predictable pattern, but every now and then it reverses direction in the sky, making a tiny loop against the background stars – this is Jupiter retrograde.

Of course, Jupiter isn’t actually moving backwards in the sky – it orbits the Sun in the same counter-clockwise direction as the other planets. So what’s going on?

In ancient times, astronomers thought that the Sun, the Moon, the planets and the stars orbited around the Earth. This helped explain the movement of the planets, but there was a problem. The planets would occasionally reverse direction in the sky – move in a retrograde direction from the way they normally go. To explain these movements, astronomers developed a complicated model of orbiting spheres, where the planets followed a spiral path around the Earth.

This model was turned on its ear by Copernicus in the 1500s when he proposed that the planets orbited around the Sun. This also elegantly explained why Jupiter has a retrograde motion, as well as the other planets. Jupiter is following a roughly circular orbit around the Sun, but it takes 12 years to complete an orbit; while Earth takes just a year for an orbit.

The retrograde motion of Jupiter actually comes from Earth catching up to Jupiter in its orbit. As Earth passes Jupiter in orbit, we’re looking back at it as we go by. Think of a car passing another car on the highway. You see the car up ahead, and then as you pass it, the car appears to be moving backwards from your point of view. It’s not actually going backwards, of course, it’s all in your perspective.

Each Jupiter retrograde period lasts about 4 months, and happen every 9 months. Consider the orbit of the Earth and Jupiter, and you can understand that this is how long it takes Earth to complete an orbit around the Sun and then catch up with Jupiter again.

Astrologers think that Jupiter retrograde indicates some kind of change of luck and fortune, but there is nothing in the science of astronomy that supports that view at all.

Want more information on Jupiter? Here’s a link to Hubblesite’s News Releases about Jupiter, and here’s NASA’s Solar System Exploration Guide.

We have recorded a podcast just about Jupiter for Astronomy Cast. Click here and listen to Episode 56: Jupiter.

References:
Wikipedia: Jupiter
Wikipedia: Retrograde Motion

[/caption]

We’ve talked about brown dwarfs here on Universe Today for years and years. These are the “failed stars”; objects with too little mass to fully ignite nuclear fusion in their cores. Instead of blazing with red, yellow or the white light of our own stars, they’re heated by the gravitational collapse of material. They’re called brown dwarfs, but you might be surprised to know that they aren’t actually brown. In fact, it’s impossible to have brown light. So what color are they?

The term “brown dwarf” was originally coined by Jill Tarter in 1975 to describe these objects, and there were other suggestions for names, like planetar and substar. But the name “brown dwarf” stuck. And here’s the problem, as described by Jill Tarter, “it was obvious that we needed a color to describe these dwarfs that was between red and black. I proposed brown and Joe (Silk) objected that brown was not a color.”

Brown isn’t a color?!

Not for astronomers. When they consider the color of a star, astronomers are talking about the wavelength of the light being emitted. Stars emit light at various wavelengths, and whatever photons are mostly being emitted are what we see. Yellow stars emit primarily yellow photons, red stars emit mostly red photons, etc. But you can’t have a star emit brown photons because the “color” brown is a de-saturated yellow. Brown dwarfs can’t be brown because it’s impossible to emit brown light. So what color are they?

Dr. Kenneth Brecher is a professor at Boston University and the primary investigator for Project LITE. This is a research project that uses a variety of experiments to understand how people see color. I highly recommend you check out the Project LITE website and take a look at the Flash experiments they have available. You’ve probably seen some of these optical illusions in the past, where spinning wheels of black-and-white can actually create different colors in our brains. Brecher demonstrated one of these color wheels for me – it’s a CD that can spin like a top. At rest, you see black-and-white, and then spin up the disk and you can see red, green and blue. Very cool stuff (totally unconnected from the color of brown dwarfs).

All you color theory folks might want to know the hexidecimal code: EB4B25. And here are the RGB values: R-235, G-75, B-37

So what color would an isolated brown dwarf look like? Dr. Brecher had a slide in his presentation that shows the color – we’ve extracted it and made it bigger. I think it looks kind of reddish orange, but then color is in the eye of the beholder.