The uppermost portion of the Sun’s atmosphere is called the corona, and is surprisingly much hotter than the Sun’s surface (photosphere)! The upper corona gradually turns into the solar wind, a flow of plasma that moves outward through our solar system into interstellar space. The solar wind is, in a sense, just an extension of the Sun’s atmosphere that engulfs all of the planets. Earth actually orbits within the atmosphere of a star!
Temperatures rise sharply in the transition region, from thousands of degrees in the chromosphere to more than a million degrees in the corona. The density of plasma falls rapidly through the transition region moving upward from the chromosphere to the corona.
We normally cannot see the solar atmosphere, including the corona. The surface of the Sun is far too bright to allow a glimpse of the much fainter corona. During a total solar eclipse the wispy corona briefly comes into view as the Moon blocks out the solar surface. A special instrument called a coronagraph allows astronomers to view the corona at other times. Some coronagraphs are used with ground-based telescopes; others are carried on satellites.
Picture Credit : Google
