94 - The Sky 
or as simple mirrors. When the needle crystals are aligned 
vertically they produce two bright spots about 22° on each 
side of the sun at the same altitude. The resulting apparition 
is that of two ghost suns accompanying the real sun, one 22° 
to the left, the other 22° to the right. Ghost suns are more 
HORIZON 
properly called parhelia or sundogs. If the crystals are vibrat- 
ing slightly in their vertical position, curved arcs will appear 
to pass vertically through the sundogs, the so-called arcs of 
Lowitz. 
HALOS WITHOUT SAINTS 
In high cirrus clouds the crystals are very much agitated 
by the winds and are oriented more or less at random. Under 
these circumstances the sundogs disappear and in their 
place a circular halo of 22° radius appears to surround the 
sun. This halo is especially noticeable around the moon on a 
cold night when it shines through high thin clouds. 
All of the above phenomena are due to the refraction of 
light through the 60° angles of ice crystals. If light shines 
through the 90° angles instead, similar effects are observed, 
but all are at an angle of 46° from the sun instead of 22°. 
Hence halos of 46°, sundogs 46° distant etc., are sometimes 
