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Active Sun Puts on Display for Earth


It was quite a busy weekend for our Sun. During the late hours of Friday, July 30, a magnificent coronal mass ejection (CME) billowed away from the eastern limb of the Sun; the source of the blast was apparently sunspot 1092. On Sunday, August 1 at approximately 0855 UTC, Earth-orbiting satellites detected a C3-class solar flare, and again, the blast came from sunspot 1092. At about the same time as the solar flare, an enormous magnetic filament erupted, stretching across the Sun’s northern hemisphere, a complex global eruption involving almost the entire Earth-facing side of the Sun.

“This eruption is directed right at us and is expected to get here early in the day on August 4,” said Leon Golub, Senior Astrophysicist with the Solar and Stellar X-Ray Group in the High Energy Astrophysics Division of the Harvard-Smithsonian Center for Astrophysics. “It’s the first major Earth-directed eruption in quite some time. We got a beautiful view of this eruption, and there might be more beautiful views to come if it triggers aurorae.”

A C3 CME suggests that there will be no disruption for power grids, satellites, astronauts on the International Space Station or navigation services on airplanes. Stronger space storms, however, can have more serious impacts. In 1989, for example, a huge solar outburst sparked a nine-hour electrical blackout in Quebec, and a more moderate blast that occurred in April apparently turned a telecom satellite into a “zombie”.

The biggest impact from Sunday’s solar storm is expected to be aurorae: Observers in the northern tier of the United States and similar latitudes should be on the watch for rippling waves of reddish or greenish light in the night sky. The northern lights have been known to dip down to Colorado or even farther south on occasion. Such displays are caused by the interaction between solar particles and Earth's own magnetic field. It’s hard to predict exactly when the wave will hit -- but you’ll maximize your chances of seeing something by getting far away from city lights and having a clear view to the north.

High speed coronal mass ejections produce major disturbances in the solar wind. Often loop-like in appearance, CMEs rise as massive clouds of material from the solar atmosphere. Dangerous, high energy, charged particles are often produced in these disturbances and, when they are directed toward Earth, often produce large magnetic storms in the magnetosphere.

A solar flare is an explosion on the Sun that happens when energy stored in twisted magnetic fields (usually above sunspots) is suddenly released. Flares produce a burst of radiation across the electromagnetic spectrum, from radio waves to x-rays and gamma-rays. Scientists classify solar flares according to their x-ray brightness in the wavelength range 1-8 Angstroms. There are 3 categories: X-class flares are big; they are major events that can trigger planet-wide radio blackouts and long-lasting radiation storms. M-class flares are medium-sized; they can cause brief radio blackouts that affect Earth’s polar regions and minor radiation storms sometimes follow an M-class flare. Each category for x-ray flares has nine subdivisions (C1-C9, M1-M9 and X1-X9). Compared to X- and M-class events, C-class flares are small with few noticeable consequences here on Earth.

According to, the timing of these events suggests they are connected, and a review of movies from NASA’s Solar Dynamics Observatory (SDO) strengthens that conclusion. Despite the ~400,000 km distance between them, the sunspot and filament seem to erupt together; they are probably connected by long-range magnetic fields. In this movie (171 Å) from SDO, a shadowy shock wave (a “solar tsunami”) can be seen emerging from the flare site and rippling across the northern hemisphere into the filament’s eruption zone. That may have helped propel the filament into space.




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