Really cool and rare solar optical illusions
Recently I stumbled upon a Wikipedia article on sundogs, which are solar phenomena that make it look like there are two or three suns in the sky rather than just one. This combined with the fact that I had just written a post about the Perseid meteor shower sparked my desire to do a post on really cool stuff in the sky. So here goes.
This bit of light in the center-right of the picture is a sundog - not the sun or moon. The real sun is behind the trees. This happens when ice crystals in wispy cirrus clouds focus light from the sun onto one spot, making it look like there is another sun in the sky. Sundogs often are seen on both sides of the sun, making it look like there are two other suns in the sky.
You’ve probably noticed by now that there appears with the sundogs a sort of circular ring around the sun. This is known as the 22º halo. It forms because the ice crystals in 
the sky are shaped like hexagons, which, unlike water droplets, always reflect light at the very same angles. The most common of these is 22 degrees, and so if you were to measure how many degrees from the sun any point on the circle is, it would come out to around 22.
Halos around the sun (and even the moon) can also be seen at other angles (like 46º, for example). However, the 22 degree halo is the most common and the brightest, and it is the only one that produces sundogs. There are also other kinds of light diffraction that can produce many different sun reflections, or “parhelia” as captured in this brilliant photo at the South Pole station in Antarctica:
You can see several phenomena here: one of the sundogs is prominent, a parhelic circle (that thin line across the picture) runs horizontally through the sundog and the sun (which is behind the person) and above you can see an upper tangent arc, almost as if it were a reflection of the halo around the sun. Given Antarctica’s climate, it’s pretty understandable why stuff like this would occur more often there than where you live, since it takes clouds of ice crystals to achieve these effects.
Most of these little tricks have to do with stuff in the Earth’s atmosphere. Consider the green flash, for example:
Why don’t we see this more often? The answer once again has to do with the bending and refraction of sunlight, but this time by the Earth’s atmosphere as a whole—which also acts like a prism, splitting naked light into its component rainbow colors. Think of it like this: water droplets can act like prisms to make rainbows, and the Earth is one big water droplet.
In a green flash, the green light is separated from the rest of the light and appears at the top of the sun. On the other hand, the opposite light, red light, appears stronger on the bottom, as you can see.
However, green is an extremely rare sky color. The sky is usually bluish, maybe red or orange at times, but never green. The moon is never green. There are reddish-orange and bluish stars—but no green ones. This photo will show you why:
Study this carefully, and notice something: You can see green—but only once the rainbow is well-defined, at the bottom left of the picture. Green is the last color to appear. You cannot see any green closer to the prism. That’s because the human eye perceives green light as clear light when it is too bright. Conditions have to be just right to see a green flash—strong atmospheric distortions to increase the prismatic effect and dim the sun enough that the light does not shine yellow or white (which, if you look at the prism photo again, dominate the early part of the rainbow coming from the prism).
One other thing: the sun and moon appear white when high in the sky, but as they get closer to the horizon, they become yellow, then orange, then coppery-colored, and finally, blood red. That’s because the light passes through a thicker slice of Earth’s atmosphere as the sun/moon sets—and the atmosphere takes the bluish portion of the light and splashes it all over the sky. That’s why the sky is blue—and that’s another reason it’s not easy to see a green flash. It’s even harder to see a blue flash, but that exists too; just look again at the photo of the big setting sun above.
That’s all I have time for for now. Catch you later.
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