Weird things are happening around Jupiter’s Great Red Spot (GRS). The iconic red hurricane that’s been swirling around in the Jovian atmosphere for at least 350 years may be flaking away. Over the past week, winds and gases in the South Equatorial Belt (SEB) — one of two prominent, dark cloud belts striping the planet’s atmosphere — are blowing past the Spot, peeling off pieces about once a week. Some of them span up to 6,200 miles (10,000 km) across.
Astronomers have seen “flakes” slough off the GRS before, but they’ve become more frequent of late. At the same time, the Spot has been steadily shrinking due to other factors. Currently 1.3 times the diameter of Earth, a century ago it was more than three times as wide. Winds and clouds are always blowing past the Red Spot, but this month they’re interacting with it and even altering its outline. A photo taken on May 22 by Australian amateur Anthony Wesley shows that it’s literally bent out of shape.
Photos reveal a large, pale “moat” of clouds called the Red Spot Hollow surrounding the Spot and outlined by twin, narrow cloud belts connecting the Spot to the SEB. You might wonder if you can see any of this in a telescope. The answer is “yes!” The GRS sports a deep orange color, and both the Hollow and dark cloud filaments passing above and below it are visible in a 6-inch or larger scope in good seeing. That’s when the air is steady enough for a clear view of the planet. Other nights, Jupiter will shimmer and bounce due to atmospheric turbulence overhead. Use a magnification of between 100x and 200x for the best views.
You’ll need to know when to look, too. Because Jupiter rotates rapidly — one spin takes just under 10 hours — sometimes the Spot’s in view and sometimes hidden on the backside. It would be nice if Jupiter rose at a convenient hour. That will happen in about a month. For now, the planet first appears in the southeast around 11 o’clock local time in late May and doesn’t get high enough for a good look until around midnight. We’re going to lose some sleep here, but this is something special, so if you have a scope, go for it.
Here are Central Daylight times when the Great Red Spot faces skywatchers in the Americas. You can easily view the GRS for about 2 hours each time it transits Jupiter — that’s when it comes around to face us directly. Add an hour for Eastern Time; subtract an hour for Mountain and 2 hours for Pacific times:
May 23 — between 4:40 to 6:40 a.m.
May 24 — between 12:30 and 2:30 a.m.
May 25 — between 6:15 and 8:15 a.m.
May 26 — between 2 and 4 a.m.
May 26-27 — between 11 p.m. and 1 a.m.
May 28 — between 3:45 and 5:45 a.m.
May 28-29 — between 11:30 p.m. and 1:30 a.m.
May 30 — between 5:15 and 7:15 a.m.
May 31 — between 1:15 and 3:15 a.m.
You can also use Sky and Telescopes GRS transit calculator. Just enter a date and you’ll get the times of the next three transits. I hope you get a chance to spot the Spot. I’ll be watching at the next opportunity. Clear (and calm) skies!