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The Shallow Sky

New Spot in Town

Akkana Peck

Photo by Christopher Go and reprinted here with his kind permission.


There’s a new spot in town! Specifically, Oval BA, previously a run-of-the-mill white oval in Jupiter’s South Temporal Band (STB), has grown in size and taken on the same faint reddish color that the famous Great Red Spot displays.

If you’ve been watching Jupiter for a while, you’ve probably seen Oval BA. It formed when three smaller white spots merged way back in 2000, but only last December did it begin, gradually, to change color from white to brown. The shift to red seems to have happened just in the last few months.

Fortunately, Jupiter is now rising early enough (shortly after nightfall) that it’s easy to catch at nearly any time of evening. Unfortunately it never gets higher than 37 degrees (and that not until the wee hours of the evening). But Oval BA may be large enough to see even when Jupiter is relatively low in the sky, at least on a relatively steady night. It’s definitely worth checking out. Be sure to keep an eye on it over the next few months to see whether the color changes with time. Perhaps it will get even redder than the Red Spot!

Regular readers will recall that I often refer to Jupiter’s larger and more famous storm as the GSfkaR: the Great Spot Formerly Known as Red. It really hasn’t been all that red in the last decade or two, and sometimes is easier to see by the hole it makes in the South Equatorial Band (SEB), which is itself red, than by the redness of the spot itself. That said, the GRS is certainly much redder than the other storms nearby, and the new Oval BA is almost exactly the same color, prompting informal names like “Red Jr.” and “the Not-So-Great Red Spot” from JPL astronomers who have studied it.

What makes the spots red? Surprisingly, nobody knows for sure. Some theories suggest that these massive storms suck material from Jupiter’s lower atmosphere up to a higher level, where sunlight darkens it, making it a sort of photochemical smog. Think about that the next time you’re stuck in traffic on 101 on a hot summer day, looking at the brown haze above San Jose.

Saturn is well placed for convenient early evening observing, still in Cancer and quite close to the Beehive Cluster (M44). Mars, too, is high in the sky as the evening begins; it’s so far away that it’s quite small now, only about one and a half times the size of Uranus, sitting above Orion like a tennis ball being served by the hunter, and at the same time off the foot of Gemini as though it was a soccer ball being kicked by the westernmost twin. On the night of March 17, Mars passes less than a degree from the open cluster M35. If you’re observing that night with a wide-field scope, it might make an interesting sight.

The moon continues its dalliance with the Pleiades this month. Early on the evening of April 1, a slim crescent moon passes right through the the center of the cluster right around sunset. Catch it as soon as the sky gets dark to get the best view, using any size telescope or just binoculars.

Venus rises a few hours before the sun but remains low in the sky by the time morning twilight overwhelms it. Mercury, too, is low in the morning sky early in the month, and will get progressively more difficult to spot as the month progresses.

Uranus and Neptune rise barely before the sun; this isn’t a good time of year to catch them. But on the night of the 18th, you can use Venus as a guide, since it’s just a small fraction of a degree to the right of the brilliant gibbous Venus. Pluto rises a bit ahead of Neptune and Uranus, and might be within reach of the dedicated morning hunter packing a large telescope.

Comet C/2006 A1 Pojmanski is visible faintly in the morning sky. This very small comet became a surprise naked-eye sight for a short time in March (alas, too late to make last month’s column deadline), but unfortunately it’s already fading as it races away from the sun. At about tenth magnitude, you’ll definitely need a telescope to catch it now. It’s technically circumpolar, off the head of Cassiopeia, but highest and easiest to spot during the hours before dawn.


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