During the Stone Age, when Neanderthals lived alongside Homo sapiens, our ancestors may have been delighted by the light of a C/2022 E3 (ZTF) comet, also known as the Green Comet, which will once again be observable from Earth. The comet’s highly elliptical orbit means it took about 50,000 years to fly past Earth again.

Astronomers discovered the comet in March 2022 using the Samuel robotic telescope, and it passed perihelion (the closest point of the comet’s orbit to the Sun) on January 12.

The comet will come closest to our planet on February 2. The greatest convergence will occur at a distance of about 0.29 AU. (about 27 million km) from Earth, according to EarthSky data.

Comets glow due to a combination of their chemical composition and sunlight. Comets that pass near the Sun are illuminated and heated by its energy, causing molecules on their surface to vaporize and fluoresce. According to NASA’s data, comas glow green when they contain cyanogen or carbon diatoms.

According to EarthSky’s data, the Green Comet may become bright to 5th magnitude when it approaches Earth. The smaller the number, the brighter the object. The apparent magnitude of the full Moon is about 11, and the faintest objects seen by the Hubble Space Telescope have a magnitude of about 30, says Brittanica. The faintest stars that can be seen with the naked eye have a magnitude of about 6.

This is not the only green comet in recent times. In 2018, Comet 46P/Wirtanen was bright enough for observers to see with the naked eye, and in 2021, Comet Leonard glowed green as it moved through its cosmic path.