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Green comet over Hesse: ZTF hurtles past Earth again after 50,000 years

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An extremely rare sight can currently be observed at night: Comet C2022 / E3 ZTF is approaching Earth. At most, it could disturb the clouds — or any other celestial body.

Oh Jeritz

Shining green, it’s sonically called C2022/E3 ZTF — ZTF for short — and it only approaches Earth as soon as every 50,000 years. With a bit of luck, the green comet can be seen in the night sky over Hesse. The Sun has just passed by and will reach its closest point on February 1st. It will still be only 42 million kilometers away.

“Nothing to the naked eye”

To find out, you have to look north. However, you will need binoculars at least. “This comet is not something I can see with the naked eye,” says Sven Melchert of the Society of Friends of the Stars in Heppenheim.

At most, in the remote, elevated corners of the Rhön, Taunus, or Odenwald, one might have a chance of detecting comet flashes with the naked eye. In any case, you should look for a place with as little annoying light as possible.

Once around the sun in 50,000 years

ZTF was discovered on March 2 of last year. And soon the trajectory calculation showed that it was called a long-period comet. At its farthest point from the Sun, it is about 2,800 astronomical units (AU) from our central star.

Specific diagram of the association of stellar friends of comet C2022/E3 ZTF

An astronomical unit corresponds to the distance between the Earth and the Sun, which is about 150 million km. So it is not surprising that the comet needed 50,000 years for one orbit. So, aside from the possibility of rebirth, now was the opportunity of a lifetime to observe the orb.

The green comet is interesting to science

Scientists attribute the comet’s particularly green glow to the presence of diatomic carbon. Researchers are particularly interested in the chemical composition of long-period comets, explains Detlev Koschny of the Technical University of Munich.

Because such comets come from far away and have relatively few orbits of the Sun, they are still quite native. “It is hoped that this will teach us a lot about the history of the solar system.”

The moon makes observation difficult

ZTF is currently found in the constellation Draco. In late January and early February, it stays near Polaris, the brightest point in the constellation Ursa Minor. “It’s easy to find,” Melchert says. The green comet will remain in the sky all night. Then it reaches its maximum apparent magnitude of 5.5.

However, moonlight should make observing difficult during this period. At the end of the month, the crescent moon sets in the second half of the night. With the full moon on February 5th, it is unlikely that good comet-watching will be possible at first.

More observation windows from mid-February

According to Sternfreunde, another possibility is in the second half of February, provided the nights are clear. The ZTF should still have an apparent mag 6 brightness. The higher the number in this unit of measure, the lighter it is. After that, it gradually disappears again into the depths of space.

There is no comparison between ZTF and Comet Neowise, which shone in the sky in the summer of 2020. “It had a brightness of 1.1 mag and was very clearly visible,” Melchert recalls. But you have no such expectations this time.

The tail always points away from the sun

Comets are composed of dust and frozen gas. Therefore they are also called dirty snowballs. Its core is a few hundred meters to a few kilometers in size. As they get closer to the sun, the gas begins to evaporate and the dust associated with it melts. Radiative pressure and the solar wind both “blow” away from the sun, creating the typical tail.

This can be millions of kilometers long. When you look at a comet, you get the impression that it is dragging its tail behind you as it flies through space. But this is deceptive. As the comet moves away from the Sun, it “pushes” its tail in front of it.

Comets are often named by their discoverers

Comets are usually named after their discoverers, such as Halley’s comet, the tailed star Hale-Bopp, or the famous Rosetta-Churyumov-Gerasimenko comet. Amateur astronomers used to play an important role in their discovery.

Comets are now being found more and more by science project groups and well-resourced institutions. For C2022/E3, it was the Zwicky Transit Facility, an international skywatching consortium. That earned him the somewhat boring name ZTF.

Alternative Evening Star Program

For those who can’t spot the comet in the sky, Melchert has a simple alternative program: “The really fun thing to do right now is to look at Venus.” Looking towards the setting sun, one cannot miss the bright evening star – even with the naked eye. “Everyone can see that now.”

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