The Green Comet: Once in 50000 Years
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The Green Comet: Once in 50000 Years

An icy visitor appearing in the night sky for the first time since the last ice age

Post by JAVEED AHMAD SOFI on Monday, January 30, 2023

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A space traveller has arrived in our night sky. It had been here before. The last time it visited the Earth was during the Upper Palaeolithic period when our planet was in the middle of the last Ice Age. Now after fifty thousand years, it has returned for its probable last visit.


A rare dazzling green comet C/2022 E3 is passing through the inner solar system, making its first trip near Earthsince the Stone Age. The comet was discovered on March 2, 2022 by Frank Masci and Bryce Bolin using Zwicky Transient Facility (ZTF) at the Palomar Observatory in Southern California. In astronomy, half-months are designated by letters. ‘A’ for the first half-month of January and B for the second half-month.  C, D, E and F for February and March half-months. Since the comet was third such object discoveredby ZTF in the first half-month of March 2022  so it was named as C/2022 E3(ZTF). At the time of its discovery, the comet was 643 million km away from the Sun or just inside the orbit of Jupiter. After subsequent observations, astronomers determined the comet to have an orbital period of 50000 years. So its last voyage through the inner solar system came during the Upper Palaeolithic Period or Old Stone Age.The latest studies had shown that this time the comet is on a parabolic path so it will move back out into deep space never to return again.

Comets are composed primarily of frozen gases that are heated as they approach the Sun and made to glow by the Sun's light. This cloud of gas is called the head or coma. As the gases warm and expand, the solar wind blows this material out, forming the tail. Most comets have two tails: a dust tail that is bluish in colour and an ion tail that is yellowish. Recent photographs have shown the comet C/2022 E3 displaying a distinct greenish colour and sprouting two tails. The green colour is likely due to the presence of compounds like cyanogen and dicarbon, a molecule made from two carbon atoms bonded together.

The comet C/2022 E3 which began its long journey in the far outer reaches of the solar system made its closest approach to the Sun (perihelion) on January 12, 2023. Although the comet became brighter but, at perihelion, the comet was still at .71 AU from Earth ( 1AU= 14,95,97,870.7 km )making it harder for naked eye visibility. After rounding the Sun, this distance will decrease by nearly 64 million km between Jan 12 and Feb 2. As a result, the comet C/2022 E3 will continueto grow brighter through the end of January. The comet's brightness is predicted to peak on Feb 2, 2023 when the comet will make its closest approach to the Earth by passing within 0.28 AU (42 million km) of the Earth. At this point, the observers hope that the comet will reach naked-eye magnitudes. Observers will be able to spot it near the bright star Polaris also called the North star. Internet websites like The Virtual Telescope Project website will host free live webcasts of the comet's closest approach to the Earth on Feb 1- Feb 2.

Astrophotographers around the world have been watching the comet as it crosses the north-eastern sky. According to NASA, comets are notoriously unpredictable but if this one continues its current trend in brightness it will be easy to spot with binoculars and it is just possible it could become visible to the unaided eye under dark skies. Observers in the Northern Hemisphere will spot the comet in the morning sky as it moves swiftly towards the northwest during January. It will become visible in the Southern Hemisphere in early February. The comet is not expected to be as much of a spectacle as the 2020 comet NEOWISE but it is still an awesome opportunity to make a personal connection with an icy visitor from the distant outer solar system.


(Author Teaches Physics at HSS Hawal Pulwama. He can be reached at:

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