Astronomers have been tracking a big sunspot group across the Sun’s disk this week, and wondering if it would release a solar flare. Sure enough, it did. Yesterday, the group, called AR1520, let go a powerful solar flare aimed directly at Earth. Just last week the sunspot group AR1515 released a similar flare. It looks like the material ejected yesterday by AR1520 will reach Earth tomorrow, and there’s a possibility of good shows of aurorae in mid-to-far northern and southern latitudes.
The AR1520 group released an X1-type flare, the weakest grade of the strongest class of solar flare. So it’s likely not powerful enough to cause serious trouble with electronics and communications systems on Earth. Much more powerful and dangerous flares, up to X28, have been observed in the past decades.
Solar flares, like earthquakes, so far defy accurate prediction. But they usually appear in regions of increased magnetic activity such as sunspots. A flare manifests as a sudden brightening of the Sun in a concentrated region of the solar disk or limb. A large amount of energy is released along with a spray of X-rays, UV light, and charged particles. When this material hits the Earth, it’s channelled by the planet’s magnetic field into the polar regions where it interacts with the upper atmosphere to cause aurorae and other magnetic activity.
There are a dozen satellites and professional telescopes monitoring the Sun for flare activity. But because flares don’t happen often, and they only last for a few minutes, catching a flare in the act is a rare privilege for an amateur astronomer. Here’s a fine image of the yesterday’s flare taken by amateur astronomer Robert Pease near Chicago, IL with a telescope equipped with a hydrogen-alpha solar filter and a Mallincam video camera. You can see the bright curved line of the flare, which is launching straight at you, just right of centre.