Green Flash on the Horizon

A lot of people have read the book or seen the movie The Great Gatsby, and one of the main symbols in both is the green flash that Jay Gatsby (Leo DiCaprio) waits for on the dock of his great love. Although life doesn’t turn out as great for Jay Gatsby, yours will be much better after reading this article because you will then understand the physics behind the mysterious green light on the horizon!

To start off the thinking process that will lead us to the physics of the green flash, let’s first think about the spectrum of light coming from the sun. The light from the sun comes into our atmosphere as white light, meaning it has all of the components of the rainbow. The yellow, orange, and some of the red components of the spectrum are then mostly filtered out by absorption from the water molecules in the atmosphere (which is also why the ocean appears blue!) 1. Violet light is scattered by air . This leaves the red, blue, and green components of the spectrum. Now, thinking about how the spectrum would be spread out spatially (similar to how it would be from a prism), we would see that we would have green in the middle of the spectrum with red and blue components above and below it, respectively.

In order to see the light, we need to isolate the green light, right? What would you think would be the best time of day to do that, what time of day would have the green light shining directly straight across the horizon? If you guessed at sunrise or sunset, you would be correct! At this point of the day, either the red components (sunrise) or the blue components (sunset) of the spectrum would be blocked, and once the sun goes far enough down, you should see a small flash of green light! Unfortunately, though, you still aren’t guaranteed to see the green flash because you need a distant horizon with a clear edge, or a very clear morning/night in order to view. However, you are now much closer to seeing the green flash! Best luck on your endeavors in this regard.

References:

  1. J. Chem. Educ. 1993, 70, 8, 612. Publication Date: August 1, 1993
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