22° halo

(Section 3.2.3.1.1)

The 22° halo (previously known as the small haloe) is the most frequently observed halo phenomenon. The small halo appears as a white or mostly white luminous ring of 22° radius with the light source (Sun or Moon) at its centre. It shows a red fringe on the inside and, in some rare cases, a violet fringe on the outside. The sky inside the ring is conspicuously darker than the rest of the sky. The halo always has a 22° radius regardless of its position in the sky. Sometimes, depending on the amount of cirriform cloud, only a part of the complete circle may be visible. The radius can be verified by using your hand and the knowledge that the approximate angle between the thumb and little finger, with an outstretched arm and fingers spread, is 20°. So, with the thumb held over the Sun, the 22° halo will be found near the tip of the little finger.