Can you explain what causes the green flash that is often seen in the Caribbean when the Sun sets?
The green flash can be seen anytime the Sun rises or sets on a clear, unobstructed, low horizon such as the ocean. Just before the Sun rises, or right after it sets, you may see a brief flash of green. This is because you are looking at the Sun through the atmosphere. The water vapor in the atmosphere absorbs the yellow and orange light, and it scatters the violet light. What is left is the red and blue-green light. Near the horizon, the Sun’s light is bent, or refracted, and it’s as if there were two Suns — a red one and a blue-green one — partly covering each other. The red one is closer to the horizon, so when it sets, you see only the fleeting edge of the blue-green disk.