Comet C/2021 A1 Leonard is flying by the Shenzhen Observatory.

Photo courtesy of Shenzhen Observatory

　　Astronomers recently said that a newly discovered comet will fly by the earth during the Spring Festival, which is the first time it has been seen in 50,000 years, and it may be directly observed by the naked eye.

This is a comet with a diameter of 1 km and a mini tail. Its number is C/2022 E3. It was first observed and discovered by the Zwicky Transient Research Facility in March 2022.

It passed the perihelion on the 12th of this month, and the perigee on February 1. If the observation conditions are good, it may be clearly visible to the naked eye.

The last time this small "green dot", which has a relationship with the earth for 50,000 years, visited the earth was in the late Paleolithic age.

　　Around the Spring Festival in 2023, 50,000 years after meeting the earth, it will come again.

Maybe this is the only chance in your life to meet it.

　　Ren Anbing, a teacher at the School of Physics and Astronomy at China West Normal University, told West China Metropolis Daily and cover news reporters that around February 1, Chengdu citizens may be able to observe this extraterrestrial visitor with the help of binoculars or monocular astronomical telescopes.

At that time, it will be about directly above Polaris, at its brightest.

If you are an astronomy enthusiast, you can also choose a place with clear weather, high atmospheric transparency, and no smog around February 1, such as Daocheng County, Sichuan, to see this comet with the naked eye.

The Shenzhen Observatory said, "Observing a comet is different from a meteor, and requires weather conditions and the brightness of the comet. We are currently observing this comet, and we have not yet taken a picture yet."

　　Visible to the naked eye in clear and haze-free places

　　C/2022 E3 was first discovered by astronomers Bryce Bolling and Frank Massey on March 2, 2022, using the Zwicky Transient Facility.

At the time, the comet had an apparent magnitude of 17.3 and was about 4.3 AU (640 million km) from the Sun.

The object was initially thought to be an asteroid, but subsequent observations revealed that it had a very condensed coma, suggesting it was a comet.

　　"When the comet was closest to the earth, its brightness was at magnitude 5.4. The smaller the magnitude value, the brighter the celestial body. The limit observable by the human eye is magnitude 6. Considering that February 1st is the eleventh day of the first month of the lunar calendar, the moonlight Brighter will increase the background brightness, so it is difficult to observe in cities and other places with the naked eye. It is recommended to prepare binoculars or monocular astronomical telescopes for observation. If you want to observe with the naked eye, you need to be clear, cloudless, haze-free, and far away from city lights Outdoors." Ren Anbing suggested to astronomy enthusiasts.

　　The last time we visited Earth was in the Paleolithic Age

　　When comet C/2022 E3 passes perihelion on January 12, the distance from the sun will be about 160 million kilometers, and when it passes perigee on February 1, the distance from the earth will be about 42 million kilometers.

Comet C/2022 E3 has an orbital period of about 50,000 years, which means that the last time it was close to the sun and the earth, human society was still in the late Paleolithic period, and Neanderthals were still living on the earth at that time .

　　West China Metropolis Daily and cover news reporters learned from the Shenzhen Observatory that on January 10 in the Shenzhen area, comet C/2022 E3 came out of the horizon in the northeast at about 1:45 a.m., and it was suitable for observation until the astronomical dawn.

Then the comet came out of the horizon earlier and earlier. From January 27th to February 2nd, the comet became a circumpolar star near the north celestial pole and never set all night.

Among them, February 1st is the closest to the earth, the predicted brightness is the brightest, and the observation conditions are the best. The only unfavorable factor is the influence of moonlight that night.

After February 10, the comet is predicted to have a magnitude of 6.5, which can only be seen with the naked eye in areas with a good environment, and then the brightness will continue to decrease, making it unsuitable for observation.

　　A small green comet with a diameter of one kilometer

　　Nicolas Bive, an astrophysicist at the Paris Observatory, said that the comet is estimated to be about 1 km in diameter and emits green light. expelled from the solar system".

The James Webb Space Telescope will also keep a close eye on the comet, but instead of taking images, it will study its composition.

　　Compared with the last "new wisdom comet" visible to the naked eye, the comet that is about to visit the earth is much smaller, but it will be closer to the earth.

"Xinzhi Comet" flew by the earth in July 2020, attracting many astronomy enthusiasts.

The last comet that was visible to the naked eye and had a relatively large impact was Comet Hale-Bopp in 1997.


Many people will be curious, why does the head of a comet glow green?

　　Comet heads usually have a green tint that becomes more pronounced as they get closer to the sun.

This can be explained by the fact that sunlight breaks down the organic molecules on the comet into binary carbon molecules, which glow green as they continue to photolyze.

Scientists have long suspected that the green glow around some comets comes from the breakdown of reactive molecules of binary carbon, a scientific study from the United States explains.

To test this in the lab, the researchers used an ultraviolet laser to strip chlorine atoms from chlorinated carbon molecules, then bombarded the remaining binary carbon molecules with high-intensity light.

This reaction requires the molecule to absorb two photons, rather than one, and then produce a green photon when the molecule breaks down.

At that point, the molecule decays and emits a characteristic green photon, the researchers report online in the Proceedings of the National Academy of Sciences.

Moreover, the experimental results are consistent with the astronomical observations.

　　"Comets are generally non-spherical, with a typical size of 10 kilometers. The largest comet that has been discovered so far is C/2014 UN271, with a width of about 140 kilometers." Ren Anbing introduced.

In downtown Chengdu, under good weather conditions, enthusiasts can observe comet C/2022 E3 with the help of binoculars or monocular astronomical telescopes.