photo #6559571

In the cold spring air of Scandinavia, app user ‘Zanten’ spotted a supermarket sweep of halo phenomena over Vallåkra, Sweden. A very thin veil of Cirrostratus cloud, composed of tiny hexagonal plates and columns of ice, has refracted and reflected the Sun’s rays to produce halos – some common, some not so common.Working down from the top of the image, there is a bright, broad, downward-curved halo with a reddish hue at its lower edge. This is known as an upper tangent arc. Its shape appears very different depending on the altitude of the Sun: shallow and downward curving when the Sun is high like this and more like a ‘V’ shape when the Sun is down near the horizon. The fainter halo immediately below, making a precise circle around the Sun, is the 22-degree halo. It is so named because pointing towards the Sun and any spot on its circle creates an angle of 22 degrees between your arms. The curved white line passing directly through the Sun and disappearing off at both sides is a parhelic circle. This can, on rare occasions, stretch right around the sky. The parhelic circle passes through the Sun, rather than around it like the 22-degree halo, and is instead centred on the zenith, the point directly upwards in the sky. The bright patch on the right of the parhelic circle, with its reddish edge towards the Sun, is a parhelion, or sun dog. Also known as mock suns, these can appear in pairs, one on each side of the Sun. And finally, at the bottom of the image, is a lower tangent arc, the below-Sun equivalent of the one at the start. Atmospheric halo phenomena reveal the hidden geometry of the heavens.