How to best observe the spectacle in the sky

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Created: 09/01/2022 09:44 am

Of: Tanya Banner

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K2 will not be as bright as Comet Neowise was seen in the summer of 2020. Despite its size, it will not be visible to the naked eye. (Iconic image) © imago images/StockTrek Images

Comet C/2017 K2 broke records when it was discovered in 2017. Now it is coming close to Earth and can already be seen with small telescopes.

Frankfurt – It was already discovered in 2017, but now the comet C/2017 K2 (PanStarrs) is only really interesting for observers on Earth. The reason: On July 14, 2022, the comet, nicknamed K2, reached the closest position in its orbit to Earth and was then particularly easy to observe from Earth – this is still possible until autumn.

Comet K2 packs a punch: when it was first spotted by the PanStarrs telescope system in Hawaii in 2017, it was thought to be the most distant comet discovered en route to the interior of the solar system. At that time it was between the orbits of Saturn and Uranus – about 2.4 billion kilometers from the Sun. It is now in the inner solar system and is already approaching its closest point, some 270 million kilometers from Earth. Since then it has continued to fly towards the sun. The comet will reach its closest point to the sun, the so-called perihelion, on December 19, 2022.

Comet C/2017 K2 (PanStarrs): When and how to best observe the comet

That’s good news for observers in Earth’s northern hemisphere: With a small telescope, the comet should be visible all summer. However, the best time for observation was not the day of the closest to Earth – the day before, the largest full moon of the year (a supermoon) was in the sky, making observations difficult because of its brightness. A few days later the moon rose after midnight, so the sky was darker and the comet was better closed.

But how do you find the comet? He can be found in the south after dark. It stays in the constellation of the Ophiuchus until about the end of July, after which it moves on and is near the star Acrab in the constellation of Scorpio. Around mid-September, in the dark, it no longer rises far enough above the horizon to be observed well. Free astronomy programs and apps such as “Stellarium”, “SkySafari” or “Star Walk” can be used to determine the exact position of the comet.

Comet C/2017 K2 (PanStarrs): What observers can see in the telescope

Those observing the comet with a small telescope should be able to see a diffuse or fuzzy patch of light (the comet’s coma) around the nucleus of comet C/2017 K2 in a suitably dark sky. Skilled observers may be able to see that the coma (mist and dust that collects around the comet’s nucleus) is larger than that of many other comets. Part of the comet’s tail may also be visible in the telescope. Long exposures of the comet should show both the comet and its tail in all their glory.

Watch the comet in the live stream

If you don’t have a telescope but still want to observe the comet, you’ll find what you’re looking for on the Internet: The Virtual Telescope Project shows the comet in a live stream, starting on July 15 at 12:15 a.m.

Comet C/2017 K2 (PanStarrs) broke records upon its discovery

Comets are mostly rocks and dust held together by ice. As a comet approaches the Sun from the frigid outer reaches of the Solar System, the ice warms and sublimates, the comet becomes active and begins to outgas. The coma and the characteristic tail of the comet appear. Comet C/2017 K2 was already active when it was discovered in 2017 – although it was still 2.4 billion kilometers from the Sun.

However, the comet’s early activity seems to have little to do with the sun. “K2 is so far from the Sun and so cold that we know for sure that the activity is not due to the evaporation of water ice like other comets,” said lead researcher David Jewitt of the University of California after observing the Comets with the ‘Hubble’ Space Telescope in 2017. ‘We believe that the activity is instead due to the sublimation of supervolatiles as K2 first entered the planetary zone of the Solar System. That’s why he’s so special. This comet is so far away and so incredibly cold that the water ice there is frozen like rock.”

Even more distant comet discovered

A comet, Bernardinelli-Bernstein, has since been discovered even further out in the solar system (4.4 billion kilometers from the Sun). It is also already active and is flying into the interior of the solar system. However, it comes no closer to the Sun than Saturn’s orbit.

Early telescopic observations of comet C/2017 K2 indicated that the comet could have a nucleus 30 to 160 kilometers in diameter. However, later observations with NASA’s Hubble Space Telescope showed that the core may be smaller, about 18 kilometers or less. Another sign that the comet might be large (or at least very active) is the size of its coma: it is 130,000 kilometers across – 10 times the diameter of planet Earth. Observations also assume that its tail is about 800,000 kilometers long.

Comet C/2017 K2 (PanStarrs) was imaged by Nasa and ESA's Hubble Space Telescope in June 2017. Visible is the comet's nucleus surrounded by the diffuse and fuzzy coma. (archive image)
Comet C/2017 K2 (PanStarrs) was imaged by Nasa and ESA’s Hubble Space Telescope in June 2017. Visible is the comet’s nucleus surrounded by the diffuse and fuzzy coma. (Archive image) © NASA, ESA, and D. Jewitt (UCLA)

Comet nuclei are usually up to three kilometers in size – K2 is larger

Most comets have a nucleus that is about one to three kilometers in diameter. Some can also be up to 16 kilometers in size. The well-known comet Hale-Bopp has a diameter of 60 kilometers, Bernardinelli-Bernstein is about 150 kilometers across. Like Bernardinelli-Bernstein, Comet C/2017 K2 is believed to have originated in the Oort Cloud at the edge of the Solar System. From there it has been traveling into the interior of the solar system for about three million years. (tab)

Observing tips and space newsletters

In addition to the comet and the super moon, numerous shooting stars can also be seen in the sky in July. You can get more such tips and references to current articles by subscribing to the free space newsletter of the Frankfurter Rundschau.

The article is in German

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