Today’s photo is one of the most incredible pictures I’ve seen. In addition to the Marquette Harbor Light and the frozen Superior shore, there’s a cornucopia of solar optics that fairly defies imagination.
Atmospheric Optics is a wonderful website, certainly the best I’ve found for describing solar phenomena in a clear and inspiring manner. Here’s a bit of decoding of what’s happening in the skies of Marquette yesterday, but definitely follow the links to explore. There’s so much information and some great photos too!
First, above the lighthouse, there’s a 22º radius halo:
…visible all over the world and throughout the year. Look out for them (eye care!) whenever the sky is wisped or hazed with thin cirrus clouds. These clouds are cold and contain ice crystals in even the hottest climes.
The halo is large. Stretch out the fingers of your hand at arms length. The tips of the thumb and little finger then subtend roughly 20°. Place your thumb over the the sun and the halo will be near the little finger tip.
The halo is always the same diameter regardless of its position in the sky. Sometimes only parts of the complete circle are visible.
There’s also a sundog, known also as parhelia or mock sun. These appear in the 22º halo, even when you can’t see the halo. You can see one at the visible base of the halo on the right:
They are most easily seen when the sun is low. Look about 22° (outstretched hand at arm’s length) to its left and right and at the same height. When the sun is higher they are further away. Each ‘dog’ is red coloured towards the sun and sometimes has greens and blues beyond. Sundogs can be blindingly bright, at other times they are a mere coloured smudge on the sky.
They advise you’ll see one or two a week if you look and if you click over you can learn about how they form & moon dogs.
Finally, we come to the circumzenithal arc (CZA), the upside down rainbow at the top:
…the most beautiful of all the halos. The first sighting is always a surprise, an ethereal rainbow fled from its watery origins and wrapped improbably about the zenith. It is often described as an “upside down rainbow” by first timers. Someone also charmingly likened it to “a grin in the sky”.
The CZA is never a complete circle around the zenith, that is the exceptionally rare and only recently photographed Kern arc.
PS: Check out Dominic B. Davis’s photo of the solar halo in the morning too!