Something in the Offing

Something in the Offing

During the early hours of Sept. 26th, something exploded behind the southeastern edge of the solar disk. NASA's Solar Dynamics Observatory photographed a massive plume of debris rising over the sun's limb:

 

 

As the inset shows, the plasma-plume was big enough to swallow dozens of planets Earth. In this case, however, Earth was not in the line of fire. The ejecta will completely miss our planet.

X-rays from the eruption registered C8 on the Richter Scale of Solar Flares. The actual intensity must have been much higher, though, because the flare was eclipsed by the edge of the sun. The underlying active region might be potent.

In a few days, the blast site will emerge into view as the sun's rotation turns it toward Earth. Then we will be able to evaluate its potential for future eruptions, increasingly geoeffective as the sun slowly spins on its axis.

 

From SpaceWeather.com



Weekend fireworks were predicted, and the sun complied. On Sunday, Sept. 28th (0258 UT), the magnetic canopy of sunspot AR2173 erupted, producing an M5-class solar flare. The sun was high overhead in Australia when Matt Wastell of Brisbane photographed the explosion:

Extreme UV radiation from the flare ionized the top of Earth's atmosphere, disturbing the normal propagation of radio transmissions around our planet. In particular, there was a limited blackout of HF radio communications and a probable loss of shortwave radio contact in daylit areas for some tens of minutes.

At the moment, we do not know if this explosion hurled a coronal mass ejection (CME) toward Earth. Based on the impulsiveness (brevity) of the flare, we think not. A final answer awaits coronagraph data from the SOHO and STEREO spacecraft.

Wastell's picture, which he took using a solar telescope tuned to the red glow of solar hydrogen, shows more than a half-dozen dark magnetic filaments winding across the face of the sun. Like sunspots, these filaments pose a threat for flares. When a magnetic filament collapses it can hit the stellar surface and explode, causing a type of "spotless" explosion called a Hyder flare.

Taking into account all of the sunspots as well as the filaments, NOAA forecasters estimate a 65% chance of M-class flares and a 10% chance of X-flares in the next 24 hours.