Is This A Sunrise Or A Sunset?

By Debra Kelly on Friday, November 27, 2015
sun
“Up in the mornin’, out on the job / Work like the devil for my pay / But that lucky old sun has nothin’ to do / But roll around Heaven all day.” —Ray Charles, “Lucky Old Sun”

In A Nutshell

Say you have a still photo of the Sun hovering over the horizon. Can you tell if it’s a sunrise or a sunset? A pair of atmospheric physicists who have done considerable research cataloging and documenting the colors that go along with the beginning and the end of the day say you can’t tell the difference. They say the two events are symmetrical and one’s just running in a perfect reverse of the other. Neil deGrasse Tyson, though, says that you can use a simple trick to bust late-sleeping movie producers trying to pass off a sunset played in reverse as a sunrise. If it’s north of the Tropic of Cancer, the Sun should be moving up and to the right.

The Whole Bushel

Telling the difference between sunrise and sunset can, at a glance, be pretty obvious—one happens at the start of the day and one happens at the end of it! That’s not really what we’re talking about here. If you take a picture of the Sun just above the horizon and the sky filled with all kinds of familiar colors, can you tell if it’s sunrise or sunset?

The answer’s a tricky one.

According to William Livingston and David Lynch, it’s unlikely you’ll be able to tell. The pair of atmospheric physicists have done some considerable research on the (minor) factors that visually differentiate a sunrise and a sunset.

The so-called “twilight phenomenon” that happens as the Sun passes below the horizon (or rises above it) are completely symmetrical. The colors just happen in reverse orders to each other, making it technically impossible to tell from a still shot whether you’re looking at sunrise or sunset.

When the Sun sets, they found there’s a particular series of colors that happen. First, the sky starts to take on a pink glow, turning to yellow. As the Sun continues to set, the colors turn blue, and a phenomenon called the twilight arch forms, a thin line of yellow light at the horizon. That’s when clouds start to cast shadows on the sky. That gradually turns into the formation of the shadow of the Earth. As the twilight arch starts to disappear altogether, the pinks and yellows fade to purples and the transition into darkness is made.

There’s also the alpenglow to factor in. About half an hour after the Sun has disappeared, it’s not uncommon for some formations, like mountains, to suddenly seem brighter. The often purple, reddish-orange glow comes from the reflecting sunlight, and it’s the purple light that’s the most mysterious. Difficult to photograph, it might not even occur for months or years at a time.

Studying and illustrating the differences between sunrise and sunset is particularly difficult, because modern technology hasn’t yet caught up with Mother Nature. There’s still no way to capture all the transitioning colors with 100 percent accuracy, making it that much more difficult to compare.

There are also variations in the colors of sunrise and sunset based on what the viewer is looking across as well. Livingston and Lynch added that looking out across an area where there’s a lot of green vegetation will add a green hue to the area just above the horizon, while similarly, a desert will add yellow-brown tints to the colors. Looking out over water is even more problematic, with the horizon obscured by darkness.

If you don’t look at colors, though, and if you have a little extra information, you might be able to tell if you’re looking at a sunrise or sunset. According to Neil deGrasse Tyson, when the Sun rises, it’s rising up and it’s heading toward the right, as long as it’s viewed from anywhere north of the Tropic of Cancer. That’s also how you can sometimes catch mistakes in movies and how you can tell the difference between an actual sunrise and a sunset running in reverse.

Show Me The Proof

LiveScience: Do Sunrises Look Different from Sunsets?
Color Correction Handbook: Professional Techniques for Video and Cinema, by Alexis Van Hurkman
Color and Light in Nature, by David K. Lynch, William Charles Livingston