If you’re watching a sunset or a sunrise, occasionally you might see a green flash or green rays from the edge of the sun just as it disappears from view or begins to peek over the horizon. This a purely atmospheric, optical phenomenon, nothing to do with surface activity on the sun. By pure chance I seem to have caught a bit whilst photographing a sunset on the North Norfolk coast recently (one of the only places in the UK where, in the middle of summer, the sun both rises and sets over the sea on the “east coast”. I don’t remember noticing the green flash whilst taking the photos, it’s only now in scanning through the files that I spotted it.
Earthsky has as interesting explanation of the phenomenon:
The green flash is the result of looking at the sun through a greater and greater thickness of atmosphere as you look lower and lower in the sky. Water vapor in the atmosphere absorbs the yellow and orange colors in white sunlight, and air molecules scatter the violet light. That leaves the red and blue-green light to travel directly toward you. Near the horizon, the sun’s light is highly bent or refracted. It’s as though there are two suns – a red one and a blue-green one – partially covering each other. The red one is always closest to the horizon, so when it sets or before it rises, you see only the blue-green disk – the green flash.