Return of the Green Comet: A 50,000-Year Celestial Reunion

Once upon an ancient sky, when Neanderthals roamed alongside Homo sapiens, both perhaps gazed up in collective wonder at a brilliant green light streaking across the heavens. Fast forward 50,000 years, and that same celestial body, the ZTF comet (C/2022 E3), has made its long-awaited return to our corner of the cosmos. This cosmic traveler, known affectionately as the ‘Green Comet,’ charts a vast elliptical orbit around our sun, taking millennia to complete its solitary journey, ensuring that its recent near-Earth approach might well be its last.

The discovery of the ZTF comet was made in March 2022 by astronomers using the Samuel Oschin Telescope at the Zwicky Transient Facility. Later, on January 12, 2023, it passed perihelion, the point in its orbit closest to the Sun. In early February 2023, sky-watchers across the United States and Japan, among other places, were given the chance to observe this rare visitor, which was visible to the naked eye under dark skies and even more so with the assistance of binoculars or a telescope. NASA recommended predawn hours for the best viewing experience.

On its closest approach to Earth on February 2, the comet was a mere 0.29 astronomical units away (around 43.45 million km). Its trajectory took it through iconic constellations such as Taurus and near Hercules, as noted by EarthSky. While its position in the vast expanse might seem elusive, stargazers could turn to astronomy apps to pinpoint its location. However, the comet was challenging to view from the Southern Hemisphere.

The comet’s green hue, an ethereal glow against the celestial canvas, is a result of its chemical composition mixing with solar light. As the comet neared the Sun, its surface molecules vaporized, and emitted light—a spectacle made possible by elements like cyanogen and diatomic carbon according to NASA. While the comet had the potential to reach a brightness comparable to a 5th magnitude star, those not able to locate it in the night sky were encouraged to use optical aids to boost their chances.

It’s worth noting that the ‘Green Comet’ moniker has been shared by other celestial wanderers, including the Wirtanen Comet in 2018 and the Leonard Comet in 2021, both glowing green enough to catch the naked eye. As we continue to look skyward on clear nights, remember to peer closely for that faint green shimmer. It just might be our long-lost spacefarer, the ZTF comet, on its possible final pass by our planet.

FAQ Section:

What is the ZTF Comet?
The ZTF Comet, also known as C/2022 E3, is a celestial body with a green hue that was discovered in March 2022. It has an elliptical orbit around our sun and its recent approach to Earth might be its last due to its long orbital period.

When was the ZTF Comet at perihelion and closest to Earth?
The comet passed perihelion on January 12, 2023. Its closest approach to Earth was on February 2, 2023, at a distance of 0.29 astronomical units (around 43.45 million km).

How could one observe the ZTF Comet?
The comet was visible to the naked eye under dark skies, and even more so with binoculars or a telescope. NASA recommended viewing during predawn hours for the best experience. Astronomy apps could help in identifying its exact location in the sky.

Why does the ZTF Comet appear green?
The comet’s green coloration is due to its chemical composition, which includes elements like cyanogen and diatomic carbon. These elements interact with solar light as the comet’s surface molecules vaporize, creating a visible green glow.

Was the ZTF Comet visible from the Southern Hemisphere?
Observing the comet from the Southern Hemisphere was more challenging.

Are there other comets known for having a green hue?
Yes, other comets like the Wirtanen Comet in 2018 and the Leonard Comet in 2021 have also been known to emit a green glow and have been dubbed as ‘Green Comets.’

Definitions of Key Terms:

Perihelion: The point in the orbit of a celestial body at which it is closest to the Sun.
Astronomical Unit (AU): A unit of measurement equal to the average distance between the Earth and the Sun, approximately 149.6 million km (92.96 million miles).
Cyanogen: A toxic, colorless gas (CN)₂ that can give off a faint glow when exposed to sunlight in the vacuum of space.
Diatomic Carbon: A molecule consisting of two carbon atoms (C₂) and is one of the reasons for the green coloration seen in some comets.

Suggested Related Links:

NASA: For more information on space observation and comet research.
EarthSky: To keep track of celestial events and view guides on stargazing.
Zwicky Transient Facility: To learn more about the telescope and facility where the ZTF comet was discovered.



Simon Smith is a renowned expert in the field of sustainable urban development. His work focuses on creating eco-friendly and efficient urban landscapes, incorporating green building practices and sustainable design principles. Smith's approach to urban planning emphasizes the importance of environmental stewardship while meeting the growing demands of urban populations. His innovative strategies in sustainable city design have influenced how urban areas globally address challenges like climate change, resource management, and ecological conservation, making him a leading voice in shaping the future of sustainable urban living.