Last Night’s Jupiter-moon Halo Plus Storms Swirl On Saturn

An ice crystal halo rings the full moon and Jupiter, visible just above the moon, last night as seen from Duluth, Minn. about 10 o’clock. Photo: Bob King

Powerful fine stuff. It wasn’t enough that Jupiter lined up with the full moon last night. Across northern Minnesota an ice halo encircled the pair for much of the evening making the show a skywatchers’ delight. Halos around sun and moon are visible any time of year, but they may be a little more common in winter, when ice crystals abound in the atmosphere.

Moonlight is refracted or bent by minute, six-sided, pencil-shaped ice crystals in cirrostratus clouds into a soft circle of light 22 degrees (about two fists held at arm’s length) in diameter. Because the blue part of light is refracted at a greater angle, halos have a pale blue outer circumference. Red is bent least, lending a ruddy tint to the inner edge.

Clouds are amazing creatures. Their shapes, growth and decay, how they create lightning, rain, halos and coronas make for endless and enjoyable study. I’m nearly as enamored of clouds as I am of stars, though a week of cloudy nights does give pause.

NASA’s Cassini spacecraft took this photo of impressive storm clouds whirling around Saturn’s north pole on Nov. 27, 2012 from a distance of about 225,000 miles away. Click to enlarge. Credit: NASA/JPL-Caltech/Space Science Institute

NASA released some wild new images of a swirling vortex of clouds ringing Saturn’s north polar region. The Cassini probe shot the photos from a high, tilted orbit for one of the most amazing perspectives on the planet’s atmosphere ever. Similar storm clouds have been seen racing around the planet’s south pole, but this is the first time we’ve had a bird’s eye view of Saturn’s other pole in visible light.

Saturn’s tipped axis means it has seasons like Earth. In 1987 its north pole was tilted toward the sun and the northern hemisphere experienced summer, while in 2005 the north pole was tipped away during Saturnian winter. Saturn is now about where it was in 1980 – northern spring. Credit: NASA

Why the long wait to see the north pole? Because it’s been in shadow for the past few years the way our north pole is in shadow (sun never rises) during the winter months. Since Saturn’s axis is tipped 27 degrees, similar to Earth’s 23.5 tilt, the planet experiences seasons, too. With one difference.

Saturn takes nearly 30 years to orbit the sun, so each season spans about 7.5 Earth years.

Wide-angle camera view of the north polar region on Saturn showing the central storm clouds inside a much bigger structure called the north polar hexagon. Can you see the six sides? Nearly four Earths could fit inside it. The feature is similar to Earth’s polar vortex where winds blow in a circular pattern. Click to enlarge. Credit: NASA/JPL-Caltech/Space Science Institute

With spring now underway in the ringed planet’s northern hemisphere, the slanted rays of the low sun graze the polar regions the way sunlight touches the treetops at sunrise, lighting up the clouds in dramatic fashion. Wish we could see that in our telescopes! Check out another photo HERE.

6 Responses

    1. astrobob

      Thanks Mike. It wasn’t easy to separate Jupiter from the moon’s glare in the time exposure. I shot at f/16 hoping the planet would show up between the brighter spikes.

    1. astrobob

      Love the illustration. While the hexagon is only 15,000 miles across or two Earth diameters, one could squeeze approximately four Earths into it in part because of the feature’s unusual boxy shape — one on the left, one on the right, one top and one bottom.

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