From APOD...
What's causing those unusual sky arcs? Ice crystals. While crossing a field of fresh snow near Füssen, Bavaria, Germany, earlier this month, the photographer noticed that he had entered an ice fog. For suspended water to freeze into an ice fog requires quite cold temperatures, and indeed the air temperature on this day was measured at well below zero. The ice fog reflected light from the Sun setting behind St. Coleman Church. The result was one of the greatest spectacles the photographer has ever seen. First, the spots in the featured picture are not background stars but suspended ice and snow. Next, two prominent ice halos are visible: the 22-degree halo and the 46-degree halo. Multiple arcs are also visible, including, from top to bottom, antisolar (subsun), circumzenithal, Parry, tangent, and parhelic (horizontal). Finally, the balloon shaped curve connecting the top arc to the Sun is the rarest of all: it is the heliac arc, created by reflection from the sides of hexagonally shaped ice crystals suspended in a horizontal orientation.
What are these two giant arches across the sky? Perhaps the more familiar one, on the left, is the central band of our Milky Way Galaxy. This grand disk of stars and nebulas here appears to encircle much of the southern sky. Visible below the stellar arch is the rusty-orange planet Mars and the extended Andromeda galaxy. But this night had more! For a few minutes during this cold arctic night, a second giant arch appeared encircling part of the northern sky: an aurora. Auroras are much closer than stars as they are composed of glowing air high in Earth's atmosphere. Visible outside the green auroral arch is the group of stars popularly known as the Big Dipper. The featured digital composite of 20 images was captured in mid-November 2022 over the Lofoten Islands in Norway.
Yes, but can your aurora do this? First, yes, auroras can look like rainbows even though they are completely different phenomena. Auroras are caused by Sun-created particles being channeled into Earth's atmosphere by Earth's magnetic field, and create colors by exciting atoms at different heights. Conversely, rainbows are created by sunlight backscattering off falling raindrops, and different colors are refracted by slightly different angles. Unfortunately, auroras can’t create waterfalls, but if you plan well and are lucky enough, you can photograph them together. The featured picture is composed of several images taken on the same night last November near the Skógafoss waterfall in Iceland. The planning centered on capturing the central band of our Milky Way galaxy over the picturesque cascade. By luck, a spectacular aurora soon appeared just below the curving arch of the Milky Way. Far in the background, the Pleiades star cluster and the Andromeda galaxy can be found.
Have you ever seen a dragon in the sky? Although real flying dragons don't exist, a huge dragon-shaped aurora developed in the sky over Iceland in 2019. The aurora was caused by a hole in the Sun's corona that expelled charged particles into a solar wind that followed a changing interplanetary magnetic field to Earth's magnetosphere. As some of those particles then struck Earth's atmosphere, they excited atoms which subsequently emitted light: aurora. This iconic display was so enthralling that the photographer's mother ran out to see it and was captured in the foreground. Our active Sun continues to show an unusually high number of prominences, filaments, sunspots, and large active regions as solar maximum approaches in 2025.