Did you know, the interactions between the sun and our planet’s atmosphere, as well as other constituents of our solar system, can create a number of other visually-stunning phenomena?
Here is a rundown of some of the lesser-known, and harder-to-catch, solar “special effects.”
When the sun rises or sets, a green flash is nearly always lost to the naked eye. The distinctive coloration results from Earth’s atmosphere acting like a prism, splitting white sunlight into its spectrum of hues. Most of the time when the sun is near the horizon, only red and orange, longer-wavelength light makes it through to our eyes. Shorter wavelengths get refracted or bent out of sight. But for a brief moment, a band of green can make it through. In very rare cases, when atmospheric conditions are just right, a blue flash can be detected as well.
Rather than risk hurting your eyes squinting at the sunset, let a camera try to capture the green flash. The odds of seeing green flashes improve when the air is stable and clear with a sharp horizon line. Gazing over the ocean provides a good vantage point for capturing the green flash.
Green flashes come in several varieties. One is sometimes referred to as a green rim, seen in the above image. The green rim actually happens with nearly every sunset but is very tough to spot. Another, rarer sort of green flash reveals itself right as the sun disappears below the horizon as a fleeting verdant specter (below). Casual onlookers can often catch such a green flash, for instance, from Kauai, Hawaii.
Belt of Venus
You’ve likely noticed this pinkish band hugging the eastern horizon after sunset, opposite where the sun has sunk in the west. It is reddish solar light backscattered—that is, reflecting back toward where it originated from with the setting sun—by particulates in the atmosphere. This phenomenon gets its name from the fact that the planet Venus, visible at dawn and dusk, is often located within or near the colored celestial stripe.
Below the Belt of Venus, the sky looks darker and purplish. This band is actually a shadow cast by Earth as its dayside rotates away from the Sun and enters night.
The ancient Greeks and Romans wrote about “mock suns” following the real sun. Surely what their eyes saw is the phenomenon now called a sun dog. It manifests as a bright spot (or spots) in alignment with the sun and appears to the sun’s left, right, or on both sides.
Sundogs are specifically caused by hexagonal ice crystals in the atmosphere, which refracts sunlight akin to a prism. This refraction can produce a great number of related phenomena, broadly classified as halos. For instance, sun dogs’ typical distance from the sun—22 degrees—falls on a halo of the same name. A glowing line can sometimes be seen extending from the sun to the sun dogs, called a parhelic circle. In these situations of highly refracted sunlight, a vertical luminescence may also protrude from the sun, dubbed a sun pillar. All these solar visuals are present in the above image.
It’s more than likely you’ve seen rainbows before. They make this list, however, because A) rainbows are inarguably amazing, and B) can you readily explain how they work?
As with other phenomena in this article, rainbows form from an interplay of reflection and refraction. Instead of ice crystals, in this case, water drops serve as the responsible prismatic party. When light enters the droplet, some of it is reflected by the drop’s far side, back the way it came in. In the process, the light gets refracted by the water, with the different wavelengths (colors) bending at different rates. As a result, when the light comes back out, it is splayed into the visual spectrum.
We see all this in action when rain is falling in front of us and the sun is shining behind us. The angle of the sunlight must be just right—about 42 degrees—in order to get the spectrum-throwing effect, more common when the sun is lower in the sky in the morning and afternoon.
To get a better feel for how rainbows occur, experiment with a garden hose on a sunny day. With the sun to your back, put your finger over the water flow to generate a fine mist. If you get the angle just so, you’ll generate a rainbow. Waterfalls, fog, and sea spray can also accordingly create the colorful arcs.
Another stunning visage our star can offer is the so-called Omega Sun, named after the last letter of the Greek alphabet. When the bottom limb of the sun is still “touching” the horizon, a mirage effect can temporarily occur, making the sun appear to pinch in and then expand back toward the ground.
Mirages occur when light passes through a layer of hot, lower-density air near the Earth’s surface. The light refracts, triggering a seeming reproduction of a part or whole of a distant object or the sky. As an optical phenomenon, we’re more familiar with mirages for fooling desperate desert travelers into believing an oasis lies ahead; instead, the apparent blue on the yonder landscape is just the refracted blue sky.
To see the final optical phenomenon, you’ll need to be under an inky black, moonless sky and away from the light pollution of civilization. After nightfall or before sunup, a sizable, tapering white glow can be witnessed extending up from the horizon. Called the zodiacal light, it is actually not an interaction between the Sun and Earth’s atmosphere, like the other examples given in this article. Instead, the luminance is a reflection of sunlight from the grains of cosmic dust out in our solar system.
This dust ranges in size from molecular motes to sand-like grains on up to bona fide space rocks. It is created by comets’ dusty, icy tails leaving material throughout the inner solar system, as well as the pulverizing collisions of asteroids.
The zodiacal light is so named because its light appears in the celestial zone dubbed the zodiac, which extends about 8 degrees north and south of the ecliptic, the plane of the circular path followed by the sun as it moves across the sky. Year in and year out, the sun makes these laps across our firmament, producing beautiful visuals for us to experience and enjoy.