Above: LASCO image of halo CME from Apr. 10, 2001.

Click here to see a movie of a Halo CME (182 kB) by Mark Wilber

The Large Angle and Spectrometric Coronagraph (LASCO) uses three different telescopes (C1 through C3) to image the solar corona - a region of hot gas around the sun - in white light. This instrument is aboard SOHO .

SOHO is a spacecraft operating at the L1 Lagrange point, a gravitationally stable region between the Earth and the Sun about 1.5 million km in space. A coronagraph is a telescope that uses a circular disk to shield out any bright source in the center of the field of view so that fainter features around the object can be imaged. The C3 coronagraph images the solar corona from ~3 to 30 solar radii away from the sun.

At one time it was thought that solar flares were the primary indicators of Solar activity, with their associated bright emissions in visible light as well as in x- and gamma-rays. More recently, Coronal Mass Ejections (CMEs) have emerged as an event that may impact the space weather conditions at other planets much more so than flares. They produce large amounts of energetic solar particles and can cause rapid changes in the interplanetary magnetic field. As these disturbances propagate outward from the sun toward the planets, a shockwave forms in which ambient solar wind particles are accelerated to very high energies - producing Solar Energetic Particles (SEPs), intense showers of particle radiation. "Halo" CMEs are of special interest to us on Earth, which describe events heading towards us and thus appear as a halo around the edges of the solar disk. Large CMEs can cause communications disruptions, power grid failures, and intense auroras at low latitudes (see Kp index for more information on the location of the aurora.)

Current CME conditions

SOHO Spacecraft Website