Scroll to the bottom of post for a sky chart of three evening planets
The green flash image at the top of this post was taken by Jim Grant, our friend on Facebook. He captured this green flash off the coast of Ocean Beach, California. He called it a mock mirage green flash.
You can see green flashes with the eye, when sky conditions are just right, if you are looking toward a very clear and very distant horizon. That’s why those who see green flashs most often see them over a sea horizon. You also must be looking just at sunset, at the last moment before the sun disappears below the horizon. And you have to be careful not to look too soon. Wait until just the thinnest rim of the sun appears above the horizon. If you look too soon, the light of the sunset will dazzle (or damage) your eyes, and you’ll miss that day’s green flash.
There are many different types of green flash. Some describe a streak or ray of the color green … like a green flame shooting up from the sunrise or sunset horizon. The most common green flash, which many people describe, is a flash of the color green seen when the sun is nearly entirely below the horizon.
You need a distant horizon to see any of these phenomena, and you need a distinct edge to the horizon. So these green flashes, streaks, and rays are often seen over the ocean – but you can see them over land, too, if your horizon is far enough away. Pollution or haze on the horizon will hide this instantaneous flash of the color green.
Here’s another good article about the green flash by Peter Michaud.
And here’s a rather subtle green flash video here. I had to watch it several times to convince myself I saw any green.
Bottom line: The green flash is legendary, and some people have told us they thought it was a myth, like a unicorn or a pot of gold at the end of a rainbow. But green flashes are very real. You need a distant and very clear horizon to see them at the last moment before the sun disappears below the horizon at sunset.