
As the sun dips below the horizon and the light starts to dim, lucky observers may spot a rare, brief flash of emerald. This is the "green flash," which can sometimes be seen right after sunset or before sunrise.
So what causes the green flash?

As the sun dips below the horizon and the light starts to dim, lucky observers may spot a rare, brief flash of emerald. This is the "green flash," which can sometimes be seen right after sunset or before sunrise.
So what causes the green flash?