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Friday, August 07, 2020

Explained: Comet C/2020 F3 Neowise, one of the brightest comets in decades passing Earth

NEOWISE Comet: Comets do not have light of their own and what humans are able to see from Earth is the reflection of the sun’s light off the comet as well as the energy released by the gas molecules after it is absorbed from the sun.

By: Explained Desk | New Delhi | Updated: July 15, 2020 10:29:13 am
Comet C/2020 F3 Neowise, Comet near earth, Neowise comet, what is a comet, comet pictures, comet video, indian express In this image released by NASA, Comet Neowise, left, is seen in the eastern horizon above Earth in this image taken from the International Space Station on Sunday, July 5, 2020. (NASA via AP)

The recently discovered comet called C/2020 F3, also known as NEOWISE after the NASA telescope that discovered it, will make its closest approach to the Earth on July 22. On the day, the comet, which takes 6,800 years to complete one lap around its orbit, will be at a distance of 64 million miles or 103 million kilometers while crossing Earth’s outside orbit.

On July 3, the comet was closest to the sun at 43 million km. On this day, the comet cruised inside Mercury’s orbit and, due to its proximity to the sun, its outer layer was released creating an atmosphere – referred to as coma – of gas and dust from its icy surface.

This atmosphere sometimes leads to formation of a bright tail of debris that can extend for thousands or millions of kilometres.

What are comets?

Comets or “dirty snowballs” are mostly made of dust, rocks and ice, the remnants from time the solar system was formed over 4.6 billion years ago. In the distant past, people thought of comets as “long-haired” stars that would appear unpredictably in the sky.

In fact, Chinese astronomers kept extensive records of these comets for centuries, including the time of their appearance, disappearance and their celestial positions, NASA says. The word comet comes from the Latin word “Cometa” which means “long-haired” and the earliest known record of a comet sighting was made by an astrologer in 1059 BC.

Comets can range in their width from a few miles to tens of miles wide. As they orbit closer to the sun, like in the case of C/2020 F3, they heat up and release debris of dust and gases that forms into a “glowing head” that can often be larger than a planet.

Comet C/2020 F3 Neowise, Comet near earth, Neowise comet, what is a comet, comet pictures, comet video, indian express Comet Neowise soars in the horizon of the early morning sky seen from near the grand view lookout at the Colorado National Monument west of Grand Junction, Colo., Thursday, July 9, 2020. (Conrad Earnest via AP)

The debris forms a tail that can stretch out to millions of miles. Each time a comet passes the sun, it loses some of its material and it will eventually disappear completely as a result. This is what NASA meant when it referred to C/2020 F3 and said, “The comet survived its recent closest approach to the Sun (on July 3), and is now headed back toward the outer solar system…”, since many comets don’t survive their close proximity to the sun.

While there are millions of comets orbiting the sun, there are more than 3,650 known comets as of now, according to NASA.

Why do they get close to the sun?

Comets may be occasionally pushed into orbits closer to the sun and the Earth’s neighborhood due to forces of gravity of other planets.

The appearance of some comets, like those that take less than 200 years to orbit around the sun is predictable since they have passed by before.

These may be referred to as short-period comets and can be found in the Kuiper belt, where many comets orbit the sun in the realm of Pluto, occasionally getting pushed into orbits that bring them closer to the sun. One of the most famous short-period comets is called Halley’s Comet that reappears every 76 years. Halley’s will be sighted next in 2062.

The less-predictable comets can be found in the Oort cloud that is about 100,000 AU from the sun, or 100,000 times the distance between the Earth and the sun. Comets in this cloud can take as long as 30 million years to complete one rotation around the sun.

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Why do astronomers study and track comets?

Astronomers study comets since they believe that they hold important clues about the formation of the solar system and it is possible that comets brought water and other organic compounds, which are the building blocks of life to Earth. Further, NASA tracks all Near Earth Objects (NEOs) that includes comets and asteroids using telescopes placed all around the Earth, as part of its NEO Observation Program.

This program has a congressionally directed objective to find, track and characterise NEOs that are 140 meters or larger in size since they can pose a risk to the Earth because of the devastation a potential impact can cause.

What does it mean to be able to see a comet?

Comets do not have light of their own and what humans are able to see from Earth is the reflection of the sun’s light off the comet as well as the energy released by the gas molecules after it is absorbed from the sun. The visibility of a comet cannot be precisely predicted since a lot depends on the way the “outbursts” of gas and dust play out determining how much of a “good show” the comet will put out for observers.

According to a 2007 article written by retired planetary scientist Donald Yeomans, only a few comets are virtually impressive so as to be called “great comets”. “Just the right set of circumstances must occur. Far from the sun, the solid portions of comets, which consist mostly of water ice and embedded dust particles, are inactive. They are not large enough to be seen with the naked eye. However, when near the sun, the icy cometary surfaces vaporize and throw off large quantities of gas and dust thus forming the enormous atmosphere and tails that make comets so visually striking,” Yeomans wrote.

Comet C/2020 F3 Neowise, Comet near earth, Neowise comet, what is a comet, comet pictures, comet video, indian express A person is looking at the Comet C/2020 or “Neowise”, which is seen in the sky over Ballintoy, Britain July 8, 2020, in this picture taken from a social media. (Image via Reuters)

“It is the fluorescing of these gases, and particularly the reflection of sunlight from the minute dust particles in the comet’s atmosphere and tail, that can make these objects so visually impressive,” Yeomans added emphasising that great comets should be viewed in dark skies.

But even this is not enough for a comet to become great, since the comet must also make a particularly close approach to the sun for it to produce “enormous quantities” of gas and dust or it should make a relatively close approach to the Earth so that it is easily viewed.

How can one view comet C/2020 F3?

It is possible to view Comet C/2020 F3 NEOWISE through binoculars or a small telescope. According to NASA, it was possible to see the comet through binoculars as of July 7 and some observers were able to view it unaided. “The good news is that right now, the comet is relatively easy to observe with binoculars or a small telescope, provided you have a clear view toward the horizon,” NASA said on its website. For those in the northern hemisphere, the comet is visible in the northeastern horizon just before sunrise.

As of now, it cannot be said if C/2020 F3 NEOWISE will be visible the way it is now when it moves closer to the Earth in preparation for its closest approach. However, if it does it will become easier for more people to spot it as July progresses. From around mid-July, the comet will be visible after sunset in the northwestern sky.

“Through about the middle of the month, the comet is visible around 10 degrees above the northeastern horizon (the width of your outstretched fist) in the hour before dawn. From mid-July on, it’s best viewed as an evening object, rising increasingly higher above the northwestern horizon. (Note that observers at lower latitudes will see the comet lower in the sky, while it will appear higher for observers farther north.),” NASA has said.

Astronauts aboard the International Space Station (ISS) were also able to spot it. On July 6, Bob Behnken, one of the astronauts who flew on SpaceX’s Crew Dragon spacecraft in May, posted images of the comet as seen from the ISS on Twitter.

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