There is a dramatic change in temperature in the corona atmosphere, being that the corona is hotter than both the chromosphere and photosphere. This temperature increase seems unusual, since heat usually travels from warmer areas to cooler areas. The corona is so hot that it cannot be contained in the confines of the sun's structure. As a result, the high-velocity solar particles are emitted from the sun in a solar wind. The point on the sun which the solar wind is ejected is called the coronal hole.
Coronal holes are dark regions that reside on both poles of the sun.
They contain a very strong magnetic field of about 3000 gauss, which is ten times the earth's magnetic field. Sunspots are aligned approximately east-west and are carried across the sun's disc by solar rotation. It takes about 13-14 days for these spots to travel across the disc of the sun from edge to edge. The dark center of the sunspot is known as the umbra, which takes up one half of the sunspot diameter of about 2000km. The umbra contains a granulation-type structure called umbral dots, which appear finer than phospheric granulation.