The green flash is a rare optical phenomenon that occurs just before sunset or sunrise. It is caused by the separation of sunlight into different colors as it passes through the Earth’s atmosphere. The green flash is usually visible for less than a second, but it can sometimes last for a minute or two. The best chances of seeing the green flash are on a clear day with a direct line of sight to the sun. You can also use binoculars or a telescope to make the flash more visible.