A sundog is a concentrated patch of daylight that’s often seen to the correct or the left of the sun and even on each side of our star within the sky concurrently.
Additionally referred to as mock suns or parhelia, which means “with the sun,” based on the National Weather Service (opens in new tab). Sundogs are a part of a household of atmospheric optical illusions together with moon haloes and the intently associated sun haloes. All of those phenomena are attributable to the refraction of daylight by ice crystals within the ambiance.
Sundogs sometimes seem as a pair of patches of sunshine with refined colours which manifest on the similar altitude over the horizon because the sun. They’ll seem in quite a lot of varieties, typically as colourful spots, or different occasions, so intense and shiny they seem like two extra suns within the sky.
Associated: Red lightning: The electrifying weather phenomenon explained
The title “sundog” is believed up to now again to Greek mythology based on Almanac, although this is not the definitive origin of the title. The title might mirror the assumption that as Zeus the daddy of all gods and the god of the sky in Greek mythology, walked his canines by way of the sky they typically appeared as companions to the sun as two “false suns.”
What causes sundogs?
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Sundogs are fashioned when mild passes by way of hexagonal plate crystals of ice, suspended in cirrus or cirrostratus clouds positioned at altitudes of round 20,000 ft (6,000 meters) and better, as much as 40,000 ft (12,000 meters).
These ice crystals will also be discovered a lot nearer to the bottom in extraordinarily chilly climates the place temperatures drop under -22 levels Fahrenheit (-30 levels Celsius) as a meteorological phenomenon referred to as “diamond dust.”
As ice crystals drift downwards their hexagonal faces are oriented roughly horizontally. Rays of daylight enter by way of a facet edge face after which exit by way of one other edge face that’s inclined 60 levels to the primary.
Taking these two refractions causes the daylight to deviate by at the least 22 levels relying on the angle at which it entered the ice crystal, based on science website Atmospheric Optics. This causes mild to ring the sun at a distance of 22degrees as sun-haloes. When the sunshine is concentrated as spots subsequent to the sun. additionally separated by 22 levels it seems as sundogs.
Suitably for a phenomenon with a canine-inspired moniker, sundogs can typically seem with ‘tails’ of sunshine stretching out from them. These tails are created by the reflection of sunshine from the vertical sides of the flat hexagonal ice crystals.
The sundog rainbow
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The inside edges of sundogs nearer to the sun are inclined to have a reddish hue than the outer edges that are blue in coloration. The middles of sundogs are usually yellow or orange. The rationale for this variation in coloration is rooted within the physics of sunshine that offers rise to the ordering additionally seen in rainbows.
Gentle from the sun is white and made up of sunshine of all completely different colours. When it passes by way of a prism the white mild of the sun is cut up into its constituent colours.
This occurs as a result of the diploma at which mild is refracted when passes by way of a medium, on this case, the ice crystal, is refracted relies on its frequency. The variation is named the index of refraction.
Low-frequency long-wavelength crimson mild is refracted much less strongly than high-frequency blue mild so crimson mild stays nearer to the sun, whereas blue mild is dispersed additional out.
The impact is just like that which causes a rainbow to seem with a set order of colours, crimson, orange, yellow, inexperienced, blue, indigo, and violet (which could be remembered with the easy mnemonic ROY G.BIV) by way of rainbows are attributable to raindrops, not by ice.
If the colours in a sundog had been extra outstanding you’d see them spreading away from the sun on this order however oriented vertically moderately than horizontally as with a rainbow.
Sundogs do not solely range in coloration, nonetheless. They’ll additionally are available in quite a lot of styles and sizes relying on the scale of the ice crystals that create them.
These hexagonal crystals not often stay precisely horizontal as they descend by way of the ambiance. Reasonably they wobble as they fall to Earth, the quantity a crystal wobbles because it descends will increase with its measurement.
Crystals that wobble essentially the most, and thus bigger crystals, create sundogs which might be taller. These can turn into so tall that ultimately, they’re troublesome to tell apart from simply fragments of a 22 diploma halo across the sun.
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Each canine has its day: The place and when are you able to see sundogs?
Sundogs could be seen worldwide and may seem at any time when the sun is above the horizon. There are, nonetheless, circumstances that not solely make sundogs extra prone to manifest but additionally enhance their brightness making them extra prone to see.
The obvious situation bettering the standard of sundogs is the proximity of the sun to the horizon. The nearer the sun is to the horizon the extra conspicuous sundogs are. When the sun is excessive within the sky daylight cannot go by way of ice crystals as simply.
As a result of sundogs are extra frequent when the sun is near the horizon, the most effective time to search for these solar illusions is within the morning or night when the sun is rising or setting.
The truth that ice is vital to the creation of sundogs means you usually tend to see them throughout winter, particularly the additional north you go.
Which means the frigid winter mornings of December within the northern hemisphere present the perfect time to go sundog looking.
Should you’re searching for gear to catch the right sundog {photograph}, our guides to the best cameras for astrophotography and best lenses for astrophotography may also help.
Extra Studying
The rationale we all know sundogs aren’t associated to a god taking his canines for a stroll might be due to Isaac Newton‘s work with optics within the 1600s. Examine what impressed Newton to experiment with prisms and light-weight and the outcomes these experiments delivered on the Molecular Expressions website which additionally lets you play with prisms your self.
Bibliography
Solar Canine, Britannica, [Accessed 12/13/22], [https://www.britannica.com/science/sun-dog (opens in new tab)]
What Are Sundogs? Rainbows Beside the Solar!, Alamanac, [Accessed 12/13/22], [https://www.almanac.com/what-are-sundogs-rainbows-beside-sun (opens in new tab)]
Solar Canine Formation, Atmospheric Optics, [Accessed 12/13/22], [https://atoptics.co.uk/halo/dogfm.htm (opens in new tab)]
What Causes Halos, Sundogs and Solar Pillars?, Nation Climate Service, [Accessed 12/11/22], [https://www.weather.gov/arx/why_halos_sundogs_pillars (opens in new tab)]
