FIG. 7.3 Coronal mass ejection A huge coronal mass ejection is seen in this coronagraph image, taken on 5 December 2003 with the Large Angle Spectrometric COronagraph, abbreviated LASCO, on the SOlar and Heliospheric Observatory, or SOHO for short. The black area corresponds to the occulting disk of the coronagraph that blocks intense sunlight and permits the corona to be seen. An image of the singly ionized helium, denoted He II, emission of the Sun, taken at about the same time, has been appropriately scaled and superimposed at the center of the LASCO image. The full disk helium image was taken at a wavelength of 30.4 nanometers, corresponding to a temperature of about 60,000 kelvin, using the Extreme-ultraviolet Imaging Telescope, or EIT for short, aboard SOHO. (Courtesy of the SOHO LASCO and EIT consortia. SOHO is a project of international cooperation between ESA and NASA.)
particles, accelerated during the flare process, can take an hour or less to reach Earth, where they can endanger unprotected astronauts or destroy satellite electronics, tte coronal mass ejections arrive at the Earth one to four days after a major eruption on the Sun, resulting in strong geomagnetic storms with accompanying auroras and the threat of electrical power blackouts, ttese various terrestrial effects of solar flares and coronal mass ejections are of such vital importance that national centers employ space weather forecasters and continuously monitor the Sun from ground and space to warn of threatening solar activity.
tte entire Universe is full of similar cataclysms, tte dark night sky, with its steady stellar beacons, may give the impression of stillness and serenity, but it is actually a place of cosmic violence. Indeed, the acceleration of energetic particles, with the associated emission of powerful, invisible radiation, characterizes much of the Universe, from black holes and pulsars to the most distant quasar. Investigations of the Sun's energetic activity provide important insights to understanding violence throughout the Universe, for only the Sun is close enough and bright enough to be studied with sufficient detail.
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