These images taken by the STEREO Ahead satellite from 3:47 to 15:47 UT, show the movement of the CME cloud, on the right of the discs, as it expands toward Earth. Credit: NASA/STEREO
On August 1st around 0855 UT, Earth orbiting satellites detected a C3-class solar flare. The origin of the blast was Earth-facing sunspot 1092. C-class solar flares are small (when compared to X and M-class flares) and usually have few noticeable consequences here on Earth besides aurorae. This one has spawned a coronal mass ejection heading in Earth's direction.
Coronal mass ejections (or CMEs) are large clouds of charged particles that are ejected from the Sun over the course of several hours and can carry up to ten billion tons (1016 grams) of plasma. They expand away from the Sun at speeds as high as a million miles an hour. A CME can make the 93-million-mile journey to Earth in just three to four days.
When a coronal mass ejection reaches Earth, it interacts with our planet’s magnetic field, potentially creating a geomagnetic storm. Solar particles stream down the field lines toward Earth’s poles and collide with atoms of nitrogen and oxygen in the atmosphere, resulting in spectacular auroral displays. On the evening of August 3rd/4th, skywatchers in the northern U.S. and other countries should look toward the north for the rippling dancing “curtains” of green and red light.
The Sun goes through a regular activity cycle about 11 years long. The last solar maximum occurred in 2001 and its recent extreme solar minimum was particularly weak and long lasting. These kinds of eruptions are one of the first signs that the Sun is waking up and heading toward another solar maximum expected in the 2013 time frame.
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