Auroras from Solar Flare Light Up the Sky
By Alan M. MacRobert
Part of Wednesday morning's aurora as seen from Metchosin, British Columbia. "What a great display here!" writes photographer Sherry Buttnor. "For six hours we had auroral activity somewhere in the sky, and often almost everywhere. Virtually every kind of auroral structure was seen, and the colors were lovely." She grabbed this snapshot with a Canon Powershot A70 camera. Photo by Sherry Buttnor.
A powerful blast of solar wind swept by Earth in the early morning hours of Wednesday, October 29th, setting Earth's magnetic field to shaking and lighting night skies with colorful auroras. The blast — a coronal mass ejection, or CME — arrived around 1:30 a.m. Eastern Standard Time (6:30 Universal Time), just 20 hours after it erupted from an extremely powerful flare on the Sun. Skywatchers as far south as California, New Mexico, and Texas who kept late-night vigils, after being alerted here and elsewhere, were rewarded with grand displays.
The solar flare (rated X-17) was the third strongest recorded since at least 1976. A couple of telescopic Sun observers even saw it happening through plain, white-light filters. (Most solar flares are visible only with a hydrogen-alpha filter.) It erupted in the midst of one of the two giant sunspot groups that are currently marring the Sun's disk — both of which are easily visible to the naked eye (through a safe filter).
The Sun on Wednesday, October 29th, with two gigantic naked-eye spot groups near the center of the disk. The double one nearest center is Active Region 10488; the one below it is 10486, which blasted Earth with a coronal mass ejection in the early morning hours Wednesday. Rotating off the western (right) limb is 10484. Watch as all the spots shift westward in the next few days. Courtesy SOHO / MDI.
With the Sun in its most active state since solar maximum passed two or three years ago, additional flares, CMEs, geomagnetic disturbances, and auroras are possible for the next several days.
The two big, naked-eye spots now in view are actually the second and third to appear during the current spot outbreak, which began on October 18th. The first one is rotating out of view around the Sun's western limb as seen in the image at right. Says Sky & Telescope's Alan MacRobert (using a #14 arc-welder's filter), "These are easiest naked-eye sunspots I've ever observed."
Remember, never look at the Sun without proper eye protection. There are a variety of ways to safely observe the Sun, many of which can be found in the solar observing section of SkyandTelescope.com.
The geomagnetic storm that accompanied the auroras was ranked G5, the most powerful rating. Major solar flares and geomagnetic storms can disrupt power transmission networks, black out some radio communications, and cripple electronics on satellites temporarily or permanently. There were few immediate reports of ill effects on Wednesday, however.
To get e-mail alerts of solar flares, CMEs, and possible auroras, subscribe to Sky & Telescope's AstroAlert for solar activity.
Sunspots are relatively cool regions in the Sun's photosphere (visible surface). They form where solar magnetic fields lock onto the Sun's churning ionized gas and hold it in place long enough to cool. The photosphere's average temperature is 5,700° Kelvin, but in a sunspot's dark center (umbra), where the field is strongest, it's about 2,000°K cooler. If you could view a sunspot by itself, it would appear blazingly bright. It appears dark only in contrast with its even brighter surroundings. The umbra of a spot is typically surrounded by a lighter penumbra, where the magnetic field allows the gas more motion.
If it's cloudy at your site, you can view the latest solar images from the SOHO spacecraft (click on "Latest Images," then "Near real time images)." Also check out SOHO's MPEG movies of growing spots and coronal mass ejections.
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