NASA's Solar and Heliospheric Observatory (SOHO) has captured images of an unusually large coronal hole on the surface of the Sun. At one point, it was so large that it covered nearly a quarter of the Sun's visible disk — a distance equivalent to 50 Earths placed side-by-side.
As dramatic as this sounds, coronal holes are nothing to worry about. The phenomenon happens every 11 years as the solar cycle comes to an end and the Sun attains its solar maximum — a regularly occurring event in which the magnetic fields on the Sun reverse and new coronal holes appear near the poles with the opposite magnetic alignment.
Photo: ESA & NASA/SOHO. Taken on July 18.
These holes are dark, low density regions located in the outermost region of the atmosphere. They contain little solar material and are significantly cooler than their surroundings, which gives them their darker appearance.
According to NASA, coronal holes can influence some aurora on Earth. After magnetic forces open them up, they spew solar material at roughly twice the speed found on other parts of the solar surface.