Sundogs, Parry Arc and a halo
ANCHORAGE, Alaska (KTUU) - We’ve all seen sundogs, those cool “fake suns” to the left or right of the sun. If you’re lucky, you can see both sundogs. The photo above, sent to KTUU by Sue Butler, has not only a full sundog but also various light arcs.
The other light arcs are rarer. The Parry Arc is the concave arc at the very top of the image. This arc was originally documented in 1820 by Sir William Parry during one of his journeys to the Arctic in search of the Northwest Passage.
Also in the image is the Upper Tangent. This is that curved line at the top that touches the 22-degree line around the sun. The Upper Tangent is directly above the sun and its “wings” spread out away from the center. “Tangent arcs form when cirrus clouds have well developed columnar ice crystals drifting with their long axes almost horizontal,” says the website atopics.co.uk.
According to atopics.co.uk, “Tangent arc rays pass through the same crystal faces as those of the 22º halo and sundogs. The essential difference in the formation of the three halos is the orientation of their crystals.
The circle around the sun is the 22-degree halo.
These phenomena are created by the sun refracting and reflecting through ice crystals in the atmosphere.
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