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Circumhorizontal arc


A circumhorizontal arc (previously known as the lower circumzenithal arc) is a near-horizon arc and extends parallel to the horizon. A circumhorizontal arc is as colourful and bright as a circumzenithal arc. The circumhorizontal arc occurs only when the elevation of the light source is more than 58°. When the Sun reaches an elevation of about 68°, the circumhorizontal arc reaches its maximum intensity. In countries north or south of latitude 55°, the circumhorizontal arc cannot be seen because the Sun is always lower than 58° there. So, this is one of the few haloes that is not visible everywhere on Earth.  When the angular elevation of the light source is about 68°, the circumhorizontal arc touches the lower part of the 46° halo, if visible. These two halo types are increasingly separated with a light source further from 46°. The arc may be visible without the 46° halo being visible.


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