FARSIDE ERUPTION: An active region located just behind the sun’s northeastern limb erupted this morning, producing an X-ray flash that registered M1.5 on the Richter Scale of Solar Flares — despite the fact that it was partially eclipsed by the edge of the sun. The true intensity of the flare was much greater, possibly X-class. The explosion also hurled a spectacular CME into space:
Type II radio emissions from the expanding cloud suggest an expansion velocity of at least 510 km/s (1.1 million mph). That’s a typical speed for CMEs.
Within a few days, the sunspot responsible for this outburst will rotate around to the Earthside of the sun. At that time, Earth-directed solar activity could increase. August and September were quiet months, but in October the sun seems to be waking up
CORONAL HOLE: NASA’s Solar Dynamics Observatory is monitoring a coronal hole in the sun’s northern hemisphere. It is the UV-dark region in this image taken during the early hours of Sept. 21st:
The white lines in the image trace the sun’s magnetic field. A coronal hole is a place where the magnetic field spreads apart, allowing solar wind to escape. A stream of solar wind flowing from this particular coronal hole is heading for Earth, due to arrive on Sept. 23-24. Its arrival could add to the impact of a minor CME expected to reach Earth at about the same time. Polar geomagnetic storms are possible early next week.
SUNDIVING COMET AND FULL-HALO CME: A small comet plunged into the sun this morning, and just before it arrived, the sun expelled a magnificent full-halo CME. Click to view a movie from the Solar and Heliospheric Observatory (SOHO):
In the final frames of the movie, the comet can be seen furiously vaporizing. Indeed, those were the comet’s final frames. It did not emerge again from its flyby of the hot sun. “With a diameter of perhaps a few tens of meters, this comet was clearly far too small to survive the intense bombardment of solar radiation,” comments Karl Battams of the Naval Research Lab, who studies sungrazing comets.
The CME (coronal mass ejection) came from an explosion on the farside of the sun. Although the CME and the comet appear to intersect, there was probably no interaction between the two. The comet is in the foreground and the farside CME is behind it.
Occasionally, readers ask if sundiving comets can trigger solar explosions. There’s no known mechanism for comets to spark solar flares. Comets are thought to be too small and fragile to destabilize the sun’s magnetic field. Plus, this comet was still millions of kilometers from the sun when the explosion unfolded.
The comet, R.I.P., was a member of the Kreutz family. Kreutz sungrazers are fragments from the breakup of a single giant comet many centuries ago. They get their name from 19th century German astronomer Heinrich Kreutz, who studied them in detail. Several Kreutz fragments pass by the sun and disintegrate every day. Most, measuring less than a few meters across, are too small to see, but occasionally a bigger fragment like this one attracts attention.
BREAK IN THE QUIET: Solar activity has been low for weeks. The emergence of sunspots AR1817 and AR1818 could break the quiet. Both pose a threat for M-class solar flares. AR1817 has already produced one almost-M class eruption:
The C8-category flare was recorded by NASA’s Solar Dynamics Observatory on August 11th at 2158 UT. Whether it is a herald of bigger things to come remains to be seen. AR1817 is almost directly facing Earth, so any eruptions this week will probably be geoeffective.
BIG SUNSPOT FACES EARTH: Colossal sunspot AR1785 is now directly facing Earth. The active region has a ‘beta-gamma-delta’ magnetic field that harbors energy for X-class flares, yet so far the sunspot has been mostly quiet. Could it be the calm before the storm? NOAA forecasters estimate a 55% chance of M-flares and a 10% chance of X-flares on July 8th.
Sprawling more than 11 Earth-diameters from end to end, AR1785 is one of the biggest sunspots of the current solar cycle. In fact, it can barely fit on the screen. Click on the dark core below to see a complete hi-res picture taken by Christian Viladrich of Nattages, France:
To take the picture, Viladrich used a filtered 14-inch Celestron telescope. All those irregular blobs surrounding the primary dark core are boiling granules of plasma as small as the state of California or Texas. It’s a very sharp picture.
M-CLASS SOLAR FLARE: Sunspot AR1778 produced an impulsive M2-class solar flare on June 23rd at 20:56 UT. NASA’s Solar Dynamics Observatory recorded the extreme ultraviolet flash:
The eruption flung material away from the blast site, but the debris does not appear to be heading toward Earth. Except for the effects of the UV flash, which created a short-lived wave of ionization in Earth’s upper atmosphere, this flare was not geo-effective.
More flares could be in the offing. In addition to AR1778, sunspots AR1775 and AR1776 have ‘beta-gamma’ magnetic fields that harbor energy for significant eruptions. NOAA forecasters estimate a 40% chance of M-flares and a 5% chance of X-flares on June 24th.
SOLSTICE SOLAR FLARE: This morning, June 21st at 03:16 UT, the sun itself marked the solstice with an M2-class solar flare from sunspot AR1777. NASA’s Solar Dynamics Observatory photographed the extreme ultraviolet flash and a plume of material flying out of the blast site:
As sunspots go, AR1777 is neither large nor apparently menacing, yet it has been crackling with flares for days. Before it rotated over the sun’s eastern limb on June 20th, it unleashed a series of farside flares and CMEs. Today’s explosion was not Earth directed, but future explosions could be as the sun’s rotation continues to turn AR1777 toward our planet. NOAA forecasters estimate a 30% chance of M-flares and a 5% chance of X-flares during the next 24 hours.
AN OUTBREAK OF MAGNETIC FILAMENTS: The sunspot number may be low, but the sun is far from blank. Amateur astronomers monitoring the sun report a large number of magnetic filaments snaking across the solar disk. Sergio Castillo captured more than half a dozen in this picture he sends from his backyard observatory in Inglewood, California:
“Filaments are popping up all over the solar surface,” says Castillo. “Each one has a unique shape and length.”
The longest one, in the sun’s southern hemisphere stretches, more than 400,000 km from end to end. “It’s one of the longest filamentary structures I have ever seen,” says veteran observer Bob Runyan of Shelton, Nebraska.
If any of the filaments collapses, it could hit the stellar surface and explode, producing a Hyder flare. Filaments can also become unstable and erupt outward, hurling pieces of themselves into space. Either way, astronomers with solar telescopes are encouraged to monitor developments.
SOLAR FLARE AND CME: Southern sunspot AR1762 erupted today, June 5th, producing a long-duration M1-class solar flare that peaked around 0900 UT. The explosion hurled a right coronal mass ejection (CME) into space, shown here in a coronagraph image from the Solar and Heliospheric Observatory:
Because the sunspot is approaching the sun’s southwestern limb, the blast was not squarely Earth-directed. In fact, it might miss us altogether. Stay tuned for further analysis of the trajectory of the CME.
Meanwhile, more eruptions could be in the offing. AR1762 has a ‘beta-gamma-delta’ magnetic field that harbors energy for X-flares much stronger than the M1-class event that occured this morning.
GEOMAGNETIC STORM: A G1-class (Kp=5) geomagnetic storm is in progress following the arrival of an interplanetary shock wave on May 31st. The source of the shock is not known; it might have been a minor CME that left the sun without drawing attention to itself. The impact sparked auroras across many northern-tier US states. This photo, for instance, comes from Christopher Griffith in Baxter, Minnesota:
“I wasn’t expecting to see any lights, but right before the midnight it broke loose and the sky lit up,” says Griffith. “Sadly the clouds quickly filled in my little window, and the auroras were gone. Just thankful for what I got so see!” Elsewhere in the USA, auroras were sighted as far south as Colorado, Maryland, Iowa, Wisconsin, and Nebraska.
High-latitude sky watchers should remain alert for auroras tonight as Earth’s magnetic field continues to reverberate from the impact. NOAA forecasters estimate a 40% chance of polar geomagnetic storms on June 1st.
