Astronomy EssentialsEarth

Oddly shaped suns and moons on the horizon

Oddly shaped suns and moons: Top half of a wavering orange moon rising over ocean.
View at EarthSky Community Photos. | Ron Mauer in Hilton Head Island, South Carolina, captured this moonrise on November 19, 2021, the evening after the partial lunar eclipse. He wrote: “The atmospheric distortion was crazy during this evening’s moonrise over the Atlantic Ocean. This image is my favorite from a number of shots, each more distorted than the next.” Keep reading to learn what causes oddly shaped suns and moons near the horizon. Thank you, Ron!

Oddly shaped suns and moons are great photo opportunities

Sunrises, sunsets, moonrises and moonsets are excellent opportunities to capture a particularly beautiful photograph. When you see them near the horizon, the sun and the moon can look distorted in the most fascinating ways. Their edges may appear jagged. Their bottom areas may flatten out or shrink into a pedestal. Nearby clouds and twilight color help make the artistic view even better.

But why does it happen? What causes the distortion in the appearance of a low sun or moon?

The answer is atmospheric refraction, the effect of light traveling through different densities and temperatures of air. Refraction is the same effect that causes a spoon in a glass of water to appear broken in two.

The fact is, when you gaze toward any horizon, you’re looking through more air than when you gaze overhead. It’s this greater quantity of air that causes oddly shaped suns and moons. At zenith (straight up) the atmosphere will be at its thinnest. That’s why professional astronomers prefer to observe their objects of interest as high up on the sky as possible (and as their telescopes allow). And that’s because it diminishes the effects of any atmospheric distortion lower in the sky.

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More atmosphere = more distortion

So we know there’s more air in the direction of a horizon. Now consider all the different ways refraction affects a sunrise, sunset, moonrise or moonset.

But it’s not only the amount of atmosphere that plays a role. There’s also the pressure, the temperature and the humidity. They all affect the air density and thereby how much light rays will be bent, or refracted, along their path.

Thus, temperatures varying with different layers of air can spread the light so you see a layered image of the object you’re looking at. In other words, the light refracts more in some layers than in others.

Chart showing 2 suns in fron of an eye. One sun is right at the front of the eye, the other one is lower. There are many layers of air between the eye and the suns.
Chart showing how the sun (or moon) becomes distorted when viewed on the distant horizon. Light from objects on the horizon are refracted by the dense atmosphere so they appear higher in the sky than they are. And the lower portion of the object is lifted higher than the top portion, making the object appear distorted and flattened. Image via Sciencia58/ Wikipedia.

More distortion = oddly shaped suns and moons

The bending of light rays in this manner is known as atmospheric refraction. Without any kind of disturbance, light would travel in a straight line, and give your eye a true image of what you see.

For objects with a small angular size – like stars – atmospheric refraction causes them to twinkle more the closer they are to the horizon.

But what about an object with a fair amount of surface area like the moon and the sun? For them, there is a change in the refractive effect along the height of it. Thus, the upper part travels through less atmosphere than the lower part, which makes the lower part more distorted.

Composite of 6 images of setting sun, distorted and 3 showing the green flash.
View at EarthSky Community Photos. | Meiying Lee of Taoyuan, Taiwan, captured this image and wrote: “At sunset on January 30, 2023, I recorded mock mirage sunset and green flashes on Mount Hehuan at an altitude of 3,000 meters. In the mock mirage sunset formed by multiple temperature inversion layers on the high mountain, the sun has various wonderful changes. When the top of the sun falls into the inversion layer, it produces a very obvious green flash.” Thank you, Meiying!

What is a green flash?

When atmospheric refraction is at its most extreme, you might see a mirage. It’s the exact same situation, the light is bent and distorts the image. But here it can be refracted so much that there’s a mirroring effect and you will see drawn out or multiple images. Or it may show displaced images so the moon appears higher on the sky than it actually is.

A well-known mirage for the sun is the sought-after green flash.

Green flash off the setting sun over the ocean and a composite panel on the left of progressing green flash.
View at EarthSky Community Photos. | Alexander Krivenyshev captured these images south of the Bahamas on November 14, 2022, and wrote: “Green flash over the Atlantic Ocean.” Thank you, Alexander!

Why sunsets are red

Additionally, light of different wavelengths reacts differently. For example, blue light (which has more energy, a shorter wavelength and higher frequency) is more affected by refraction than red light. That means red colors have a larger chance of coming through to you than blue. That’s why sunsets, sunrises and the moon appear redder near the horizon.

The result of refraction is nature’s own form of art, perhaps reminiscent of impressionism. Maybe that is why we find it so appealing. The video below, captured by Mike Cohea, beautifully shows the effect of the thicker atmosphere as the young moon sets over Newport.

So, go out, bring your camera and keep watching the horizon (but never stare directly, or through a camera, at the sun). Then submit your best results to EarthSky Community Photos. We love seeing your photos!

Photos of oddly shaped suns

Distorted sun setting over the ocean.
View at EarthSky Community Photos. | Meiying Lee of Taoyuan, Taiwan, captured this omega sunset on December 23, 2022, and wrote: “Today the weather is fine but the wind is very strong, and there is smog. It becomes difficult to photograph the setting of the sun by the sea.” Thank you, Meiying!
Black sky with a orange sun with bits of it missing on the sides.
View at EarthSky Community Photos. | Christopher Wagner in Los Osos, California, took this photo of the sun on July 13, 2023. Thank you, Christopher! This is a great example of a mock mirage, you can read more about atmospheric phenomena here.

Photos of oddly shaped moons

Large pink moon in lavender sky ascending above the ocean.
View at EarthSky Community Photos. | Ragini Chaturvedi was at Old Bridge, New Jersey, when she captured this image of the rising, nearly full moon. She wrote: “This evening’s almost full moonrise at 99.5 % illumination. Hunter Moon, across the Belt of Venus, right above the horizon.” Thank you, Ragini!
Orange moon against dark sky with a sliver of reflection below it.
View at EarthSky Community Photos. | Greg Diesel-Walck in Ormond by the Sea, Florida, captured this photo on December 1, 2020. The atmospheric refraction gives the seemingly melting moon a reflection, a mirage.
Moon rising over water under a bridge, sitting on a
View at EarthSky Community Photos. | Chris Mannerino captured this omega moonrise on November 28, 2020, in San Diego, California.

Bottom line: The amount of atmosphere between your eye and what you observe determines how much distortion you will see. This phenomenon – atmospheric refraction – is why the sun or moon may appear flattened near the horizon.

Read more on atmospheric refraction and mirages, with images and explanations, at Les Cowley’s website Atmospheric Optics

April 26, 2023
Astronomy Essentials

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