Astro Bob blog: Bottoms up!A new way of seeing Jupiter plus it's time to keep watch for pollen coronas around the moon.
By: Bob King, Duluth News Tribune
This looks crazy but it's a true view of the planet Jupiter as you'd see it "bottoms up" from under the south pole. This perspective is called a polar stereographic projection and it's compiled from images taken by the Cassini spacecraft in March 2000 during its Jupiter flyby. High res image HERE. Credit: NASA/JPL/Space Science Institute
The Cassini spacecraft's primary mission was and still is the planet Saturn, where it's been in orbit since 2004. En route it passed near Jupiter and photographed the planet up close. The pictures sent back allowed scientists to create the most detailed maps ever of the giant planet. Each map is composed of 18 images shot in two colors every hour for nine hours as the planet rotated beneath the passing spacecraft.
We see a variety of colorful cloud features, including parallel reddish-brown and white bands, the Great Red Spot, swirly chaotic regions, white, grey and red ovals and many small vortices. Many clouds appear in streaks and waves due to continual stretching and folding by Jupiter's winds and turbulence. The bluish-gray features along the outer edge of the map are equatorial "hot spots". To really appreciate the cloud details, be sure to click on one or both of the high resolution image links in the captions.
A polar stereographic projection of Jupiter's northern hemisphere. The equator is the outmost edge of the circle while the pole is at center. Hi res image HERE. Credit: NASA/JPL/Space Science Institute
Small bright spots within the orange band north of the equator (map directly above) are lightning-bearing thunderstorms. The polar regions shown here are less clearly visible because Cassini viewed them at an angle and through thicker atmospheric haze. Winds typically blast about 225 mph in the planet's upper atmosphere but have been clocked up to 375 mph. In comparison, a Category 5 hurricane on Earth sports winds of around 155 miles per hour.
North's at top and west to the left in this cylindrical projection of the planet Jupiter created using the Cassini photos. Credit: NASA/JPL/Space Science Institute
A more familiar way to look at Jupiter is the cylindrical projection where the entire planet is flattened out into an unwrapped cylinder. Here north and south and east and west are a little more obvious, and the planet's equator slices through the middle of the projection. For an animation of Jupiter's cloud belts in motion, take a look at this movie version of our static map. Be sure to give it a minute or two to download.
Last night's lunar halo corralled the planet Mars and several bright stars. Details: 15mm lens at f/2.8, ISO 400 and 10-second exposure. Photo: Bob King
Clouds blew by the moon last night as fierce gusts of wind swept through the trees and fields. A continual series of halos, some broken and some full, ringed the moon as tiny ice crystals in the clouds refracted the light into a circle 44 degrees or better than four outstretched fists in diameter. Caught up in those halos were the planet Mars, Castor and Pollux in Gemini and Procyon in Canis Minor.
A oval-shaped pollen corona from June 2008. To see coronas more easily it helps to hide the bright moon behind a tree, power pole or rooftop. Most water-produced coronas are circular in contrast. Photo: Bob King
With the ice gone and pollen-producing trees and plants back at it again, this is a good time to be on the lookout for pollen coronas. Coronas are small, bright and sometimes colorful disks of light very close to the moon. You'll often see them when the moon is covered by a thin cloud deck. Most coronas are caused by tiny water droplets within the clouds that diffract the moon's light and create one or two small, colored disks around the moon. Pollen coronas also form by diffraction but assume odd, elongated oval shapes. If you're ever outside under what appears to be a completely clear sky and you see a glowing oval disk centered on the moon, you're probably seeing a pollen corona.