Red sprites occur above large thunderstorm systems and are generally associated
with larger positive cloud-to-ground flashes far below. They are most luminous
very high up in the atmosphere, between altitudes of about 25 and 55 miles. Yet
even at their most luminous, they are very hard to see, in part because they
last for only a few thousandths of a second. Red in color and often bearing
faint bluish tendrils extending downward, sprites come in several shapes,
designated by colorful names like "carrot," "angel," and "columniform."