Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2001 March 1 Maximum Sun Credit: SOHO - EIT Consortium, ESA, NASA

Explanation: Astronomers recently witnessed a rather serious solar event, as the Sun's north and south magnetic poles changed places! But, this complete solar magnetic field flip was actually anticipated. It occurs every 11 years during the maximum of the solar activity cycle. Plagues of sun spots, flaring active regions, and huge prominences are also hard-to-miss signs that the solar maximum is here and on February 12, the sungazing SOHO spacecraft captured this dramatic image of an enormous prominence above the Sun's limb. Seen at the lower right, streams of relatively cool dense plasma are lofted along looping magnetic field lines extending outward about 30 times the diameter of planet Earth. Far above the limb at the upper right, a disconnected ghostly arc surrounds a dark cavity with bright central emission. These features are telltale signs of a coronal mass ejection -- yet another violent expulsion of material from the active Sun. Large, intensely bright active regions also mottle the solar surface in this image, recorded in the light of energetic Helium atoms by the Extreme ultraviolet Imaging Telescope onboard SOHO.