EIT observation of a Moreton wave expanding across much of the Sun?s surface. The wave was promulgated by a coronal mass ejection (CME) initiation site on 12 May 1997. This "running difference" imaging technique emphasizes the changes between successive frames. The wave front travels at speeds of about 300 km/s. These images were formed in the emission lines of Fe XII near 195 Ôø_ ? this ion is formed at temperatures of about 1.5 million degrees.
