The Physics of a Beautiful Sunset

15 Feb

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One of the most lasting memories of my trip to Southern California to watch the Alabama Crimson Tide play the Texas Longhorns in the 2010 BCS National Championship Game, was of the pristine, gorgeous sunsets that accompanied me each night as I finished my daily run on the beaches that hugged the Pacific Ocean.

The above picture is my favorite of the many that I snapped that week. Just looking at it allows me to feel the cool California breeze rustling against my shirt, cooling me from a well-deserved 5-mile run alongside the Pacific as I dreamed of an Alabama National Championship (something that ultimately took place, as the Crimson Tide defeated Texas 37-21 on Jan. 7).

Upon arriving to my hotel in Newport Beach, I made it a point to take a 45-minute run alongside the beach right before dusk to be able to take in the epic grandeur that presented itself on the sands of the So. Cal. beaches each and every night.

There are many locations out West, Southern California being one; Texas being another, that come to mind where the beauty of a sunset is seen and enjoyed like no other place on Earth. The magnificence and sheer elegance to behold is mind-blowing enough. And that’s before we even begin to explore the science of a beautiful sunset.

Enter this rather picturesque (pardon the pun), blog on the physics of a sunset.

As our blogger explains, the first part of a beautiful sunset is in the coloration of the Sun – the change in color it goes through as it sets. What causes that? Why it’s none other than the Earth’s atmosphere.

As the sun lowers its light needs to pass through more and more of the atmosphere to reach our eyes. As this is happening, the bluer wavelengths of light get scattered away, leaving only the reddest wavelengths that reach your eye. As the sun drops towards the horizon, it progressively loses violets and blues, then greens and yellows, and finally even the oranges, leaving only the reds behind.

Also, despite its red appearance, there really still is blue and green light coming from the Sun, of course, while this is going on. But these shorter (i.e., bluer) wavelengths refract slightly more than the lower frequency ones, meaning that the reds come in at a different, shallower angle than the greens and blues, that come in at a slightly steeper angle.

Given a clear path, to the horizon — such as over the ocean — (like in the picture above) there is a slight region of space just above the reddened Sun where only the shorter wavelength light is visible. When that happens, in addition to the normal color gradient that comes with a sunset, you can also get a small, separate region above the disk of the Sun that appears yellow, green, or even blue.

 

So now when looking at a sunset – and observing the color gradient – you should see a red lip at the bottom, or a yellow, green, or blue rim at or above the top. Hopefully, knowing the science behind the beauty helps you enjoy a sunset even more.

 

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