Discover the ghostly green lightning phenomenon

Green lightning is an optical phenomenon that occurs just after sunset or before dawn. The observer will see a green (green) spot appearing every 1 or 2 seconds just above the peak of the Sun, or possibly as a green flash of light shooting up from the point where the Sun sets. Green lightning can also appear when the Moon or bright planets such as Venus and Jupiter rise or set on the horizon.

Green lightning can be observed from any altitude (even from an airplane). This phenomenon is often seen in places where the view to the horizon is unobstructed, such as ocean waters.

Green lightning is essentially an optical phenomenon.

The main reason for the formation of the green lightning phenomenon is that sunlight (white) when passing through the Earth's atmosphere will be refracted depending on the wavelength of the light ray and separated into spectral colors. Blue light rays are refracted the most, followed by green then yellow and red.

When the setting Sun rises to about 1/60 of the Sun's diameter on the horizon, the Sun's edges can be observed with colors varying from red to blue. When the red and then yellow fringe disappears, the green and blue fringes remain on the horizon, however, the blue is scattered so much in the atmosphere that it is difficult to see. Only green (in the spectrum between yellow and blue) remains and is usually visible within a few seconds.

Earth's atmosphere, with its varied gas density, can also refract light . That's why people sometimes see rainbow halos around the Sun or mirages in the distance, according to Jan Null, a meteorologist in California. Refraction becomes very apparent as the Sun gets closer to the horizon because the sunlight is entering the thickest part of the atmosphere at a very narrow angle. This is when green lightning can appear.

Most green lightning is divided into two types. The first type appears just before the Sun disappears. However, the type that Null encounters more often is when the Sun is still above water . "You'll see this flash on top of the Sun's disk ," he said.

However, under favorable conditions, blue or even purple flashes can also be observed.

Green flashes can appear when the Sun sets over the sea. (Photo: David McManus).

To see green lightning, observers need the right conditions . First, they must see the Sun when it is near the horizon, for example on the coast or high in the mountains, according to Courtial. In coastal areas like San Francisco, Null said, the likelihood of seeing green lightning is higher on warm days, when there is a layer of warm air above cold water. These layers of air help refract sunlight.

Observation of green lightning also depends on substances in the atmosphere . The particles can scatter blue and purple light, making green light clearer. Courtial proves this with a simple experiment: Put milk powder in a tank filled with water and shine a white bicycle light on it. "When you add the right concentration of particles, you see a brilliant green color ," he said.

In addition, to see green lightning, observers also need to do this on a clear day where they can view the Sun without obstruction. However, be careful not to look directly at the Sun without eye protection.

Green flashes usually appear for less than a second. But if lucky, the observer might see them for a minute or two. Null also rarely makes such observations, despite having studied green lightning for 45 years. Green lightning can maintain its existence if atmospheric conditions are stable enough, he said.