Science & Tech

After 50,000 years, a green comet approaches Earth

The rare green comet, which last visited Earth about 50,000 years ago, has returned to the skies. If the sky conditions are just right, C/2022 E3 (ZTF) can be seen with the naked eye.

What are Comets?

  • Comets are frozen rocky or gas-filled objects that are remnants of the formation of the solar system.
  • They tend to leave a light “behind them” due to their composition, characteristics, and movement path.
  • The comet itself is green (called the comet’s head) and emits a whitish light behind it (often called the tail of the comet).
  • Comets, like other celestial bodies, have orbits.
  • Because of the sun’s gravity, they are sometimes drawn in close to the sun.
  • As they approach the Sun, they heat up and spew gases and dust into a glowing head the size of a planet.
  • To humans on Earth, the resulting dust trail looks like a trail of light from a distance.

What is Green Comet C/2022 E3 (ZTF)?

  • Comet C/2022 E3 (ZTF) was discovered by the wide-field survey camera at the Zwicky Transient Facility in March of last year, when it was already inside Jupiter’s orbit.
  • While initially thought to be an asteroid, it began to develop a tail as the Sun’s influence began to vapourise the ice.
  • It was discovered with a magnitude of 17.3 when it was discovered.

Why is it green in colour?

  • Comets have been observed emitting blue, whitish, or even green light.
  • In this case, the green glow is thought to be caused by the presence of diatomic carbon – pairs of carbon atoms bound together – in the comet’s head.
  • When excited by ultraviolet rays from solar radiation, the molecule emits green light.

When and where can you see the green comet?

  • Northern Hemisphere observers will see the comet in the morning sky as it moves quickly toward the northwest during January.
  • In early February, it will be visible in the Southern Hemisphere.
  • When looking northwest in Indian skies, it can be found 16° above the horizon in the Bootes constellation.
  • However, with the lights from buildings and streetlights on, it can be difficult to see without equipment.

Is the green comet uncommon?

  • It last appeared in the skies above Earth during the Upper Paleolithic period, when Neanderthals roamed the planet and early Homo sapiens were just beginning to emerge.
  • The green comet belongs to the category of long-period comets, which take more than 200 years to orbit the Sun.
  • The comet’s highly elliptical orbit will take it back to the Oort cloud, where it will reappear roughly 50,000 years later.
  • However, due to their orbits, it is not uncommon for comets to reappear close to Earth after many, many years.
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