Sunspot’s Parting Gift — A Spectacular Loop Prominence / Aldebaran Goes Bye-Bye

A stunning and rare loop prominence arches over departing sunspot group 2673 in the aftermath of an X8-class flare Sunday afternoon (Sept. 10). The Earth is shown for size comparison. The prominence is composed of high-temperature, ionized hydrogen — blazing-hot plasma — that outlines the shape of the powerful magnetic field in the group. Credit: Dave Snope

What a sunspot show it was. The huge group, AR 2673, visible with the naked eye, produced an X9.3 flare on September 6th, the most powerful recorded since 2005. For the next few days, it quieted down a bit and then went ballistic again. At 11:06 a.m. Central time Sunday, the region erupted with at the sun’s western limb with a parting gift — an impressive X8-class flare.

The X8-class flare, seen here in far ultraviolet light by NASA’s Solar Dynamics Observatory on September 10 (left) set the stage for rare loop prominence just hours later. Click here for a color video of the prominence in action. Credit: NASA (left) and Tim Connolly

Not long after, a rare loop prominence at least seven times the diameter of Earth, spun out from the group, making for one of the most beautiful displays of solar power ever witnessed. Loop prominences are a special variety of the pink “flames” many of you got to see around the sun’s edge during the August total solar eclipse. Prominences are made of hot gas suspended in magnetic fields that arise at the surface of the sun.

If you look closely at this 40-minute animation of the loop prominence, you’ll see solar gases circulating up and around. Gases will also flow back down the “legs” to the sun’s surface. Credit: Glenn Graham

Loop prominences form in the aftermath of large solar flares and can last up to a day. The distinctive shape of the prominence results from strong magnetic fields in sunspot region 2673 bending the hot plasma into a loop. Their tightness and symmetry of the nested loops are clear indicators of the magnetic muscle of this region. With any luck, the group will return to view along the sun’s eastern limb in two weeks with more in store.

In other observing news, the waning gibbous moon will occult (cover up) several bright stars in the Hyades star cluster in Taurus including first magnitude Aldebaran tomorrow morning, September 12th. For much of the Americas, the cluster star occultations will happen in the wee hours before dawn. The most notable will be the bright double Theta-1 and Theta-2 Tauri (θ1 and θ2) around 4:15 a.m. Central time. Aldebaran’s turn comes after sunrise for the eastern half of the U.S. and in twilight for observers in the western half.

This view shows Theta-1 Tauri just emerging at the moon’s dark limb tomorrow morning as seen from Minneapolis, Minn. Created with Stellarium

Having seen an Aldebaran occultation in daylight, I can tell you, it’s easy to see in a small telescope about 4.5 inches or larger provide your sky is clear and free of haze. First, sight the moon, then look carefully along its bright edge for Aldebaran, which will look like an orange-red spark. It’s kind of cool to see a star in the daytime, and the moon will make it easy. For viewing any of tomorrow’s occultations you’ll need to know the time when the stars disappear at the moon’s advancing bright limb (east side) and when they’ll reappear along the dark, shadowed limb (west side).

The Aldebaran occultation will be seen across the country but after sunrise in the eastern half. Created with Stellarium

Click on the links below for each occultation, and you’ll be shown a list of cities along with times of disappearance and reappearance. Times are UT or Universal Time. To convert to your time zone, subtract 4 hours for Eastern Daylight; 5 for Central; 6 for Mountain and 7 for Pacific. Be sure you’re out watching about 10 minutes before disappearance or reappearance. Because stars are so tiny at their distance and the moon has no atmosphere, they disappear and reappear in a sudden “wink” that’s a thrill to see.

θ1 Tauri occultation 

θ2 Tauri occultation

Aldebaran occultation

Good luck and clear skies. Special thanks to Tim, Dave and Glenn for their wonderful images.