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The Shallow Sky

Saturn's swirling snowstorm

Akkana Peck

Amateur astronomer Christopher Go took this image of the storm on March 13, 2010. The arrow indicates the location of the storm and the red outlines show where Cassini’s composite infrared spectrometer gathered data. Image credit: C. Go and NASA/JPL-Caltech/GSFC


Saturn is beautifully placed for viewing, up high at nightfall, with rings still tilted nearly edge-on to us: they’re tilted only about 1.7 degrees.

Last month I wrote about a few of Saturn’s plethora of moons. But moons and rings aren’t all there is to see on Saturn: you can watch some weather, too.

Weather on Saturn is a lot more subtle than on Jupiter. I remember, as a kid, looking through the Jason 60mm refractor I’d found at a garage sale and seeing Jupiter’s equatorial bands and polar regions. You need a bit more equipment than that to see weather on Saturn.

But recently we got a reminder of the value of amateur Saturnian weather-watching. In March, noted amateur astrophotographer Christopher Go, using his C-11 in the Philippines, shot an image of Saturn that showed a new and massive blizzard gaining strength. Go and Australian amateur Anthony Wesley emailed the Cassini project with pictures of the storm.

The Cassini team was able to image the area a few weeks later with the spacecraft’s composite infrared spectrometer. They found unexpectedly high levels of phosphine being pushed up from lower levels of Saturn’s atmosphere, indicating powerful updrafts driving the storm. Cassini scientists say there’s probably a fierce ammonia-ice blizzard about 100 km below the bottom of Saturn’s stratosphere, probably driven by fierce storms another 100 to 200 km lower, involving lightning and clouds of water and ammonia.

Somehow that makes the drizzle as I’m writing this column seem a lot less significant.

This isn’t the first time in the spotlight for either Go or Wesley. Go was active in imaging Jupiter’s “Spot Jr” a few years ago, and has even worked with the Hubble Heritage team imaging a quadruple Saturn moon transit, while Wesley was in the news last summer for discovering a new dark spot on Saturn.

For the March Saturn storm, they were responding to an alert that went out in February that Cassini’s radio and plasma wave instrument was showing increased static, possibly indicating a large storm.

So how should amateurs get involved? Try joining some of the active Saturn observing lists – perhaps some of the ALPO lists on Yahoo Groups – and see what hot new feature everybody’s talking about.

If you do imaging, consider making a web page showing how your images change from day to day. Remember, scientists get a lot of amateur images submitted, and they aren’t looking for pretty images so much as how features on the planet are changing. Go himself has a great example of that sort of page, including details about his observing setup, at:

But enough about Saturn. Early on June evenings, before you swing up to Saturn, check out Mars and Venus in the western sky. Venus stays low, while Mars is in the belly of Leo.

Pluto is at opposition on June 25th, so this marks the beginning of Pluto season. Unfortunately, it’s located in a very tough field – northern Sagittarius, right in the heart of the Milky Way. That means lots of guide stars, but it also means lots of stars to confuse with faint Pluto. As if that weren’t enough, it’s not just any old central Milky Way location, but right on the edge of M24, the Sagittarius star cloud. And at magnitude 14, Pluto is right about the same magnitude as a lot of those M24 stars. So go after Pluto – but make sure you have a very good chart of the M24 region prepared first.

Jupiter, Uranus and Neptune are morning objects all this month, with Mercury making a morning appearance at the beginning of June but disappearing behind the sun a few weeks later. Early in the month, Jupiter and Uranus make a close pass, getting within half a degree on the morning of the 6th.


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