The figure below shows images of a coronal mass ejection (CME) taken with two instruments on the Solar and Heliospheric Observatory (SOHO). CMEs are large explosive events on the Sun that can release high energy particles and billions of tons of cooler plasma into interplanetary space.

On the left is a white-light image of the Sun that was taken with the LASCO/SOHO coronagraph. The white circle represents an outline of the solar disk. The dark brown area is the part of the solar atmosphere that is blocked by LASCO's occulting system. On the right side of the figure are two images of the CME in ultraviolet light. They were reconstructed from observations with SAO's Ultraviolet Coronagraph Spectrometer (UVCS/SOHO). The upper UVCS image shows the CME as it appears in light produced by neutral hydrogen, while the lower image depicts the speeds of neutral hydrogen atoms moving toward (blue) and away (red) from the observer. Both of these images use false color, the former to represent the intensity of the H I Lyman-alpha radiation (ranging from black to orange to white) and the latter to indicate the direction and speeds of the hydrogen atoms (dark blue, white and red representing the highest speed toward the observer, zero speed and the highest speed away from the observer, respectively). The green line nearest the Sun represents the location of the base of the ultraviolet images, which is at 2.3 solar radii from Sun-center.

The upper UVCS image shows the same general morphology as the LASCO image. The outer portion of this image shows the bright compressed CME front. The low-intensity cavity (dark area) can be seen just below that. The bright prominence material is represented in white.

The lower UVCS image shows that the compressed CME front (blue area) is moving toward the observer with its top part (darker blue area) moving faster than its lower right side. The trailing prominence material below the CME front has a more structured pattern of speeds but it is mainly moving away from the observer.

The UVCS observations provide unique information even though the reconstructed images are somewhat distorted compared to the LASCO images. UVCS detected emission from spectral lines of hydrogen, oxygen, silicon, and carbon in this CME. Line widths and intensities provide information about proton, electron, and ion temperatures, bulk 3D flows, elemental abundances, the ionization state of the plasma, and its helicity (the handedness and geometry of the twisted magnetic field).