Sigmoids Predict Solar Eruptions.

On the Sun , S marks the spot. Solar explosions have been discovered to explode preferentially from regions marked with this letter. The surface of the quiet Sun is a maze of hot gas and flowing magnetic fields . When two regions of high magnetic field strength approach each other, they typically pass uneventfully. If the two regions pass close enough and in just the right way, however, an X-ray bright S-shaped region called a sigmoid forms and quickly explodes in a Coronal Mass Ejection (CME). Astronomers conjecture that in the center of the sigmoid, a circuit closes that somehow drives the explosion. The above picture shows the Sun in X-ray light. A pre- CME sigmoid is shown on the left inset image, while a post- CME arc is shown in the right inset.