Upper Tangent Arc
November 19, 2001
Provided by: Atmospheric Phenomena
Summary authors & editors: Jim Foster
The above photo shows a halo phenomenon known as the upper tangent arc. When cirrus clouds contain columnar ice crystals aligned so that their axes are all in a horizontal direction, this type of arc may be produced. A characteristic of this arc-shaped patch of light is that it's directly above the Sun (it bends upward away from the Sun), and it's approximately 22 degrees away from the Sun itself - about 2 fists held at arms length. With the Sun lower in the sky at this time of year, many halo phenomena are easier to see than in the summer when the Sun's high in the sky - we just don't spend much time looking up. Notice also the Sun pillar just above the Sun.
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