Children

A snowball in space

It is believed that the last time it graced the Earth’s skies was around 4,500 years ago. The next time it will visit us will be about 6,800 years from now. Say hello to Comet NEOWISE as it streaks by, giving us a rare celestial treat.

Cosmic wonders

Comets are dusty snowballs. They orbit the Sun just like planets do. They contain frozen gases, rock and dust, and are basically leftovers from the formation of the Solar System. When they go close to the Sun, they heat up, and the dust and gases form a tail – a distinctive feature of comets. Comet tails always point away from the Sun.

There are probably billions of comets orbiting the Sun. Occasionally a comet will pass through the inner Solar System and get close enough for us to spot it from the Earth. If we are lucky enough, we might even be able to see it without a telescope or binoculars. Halley’s Comet, arguably the most famous comet in the world, was last seen in 1986. It becomes visible from the Earth every 75-76 years. Another memorable visitor was the Hale-Bopp comet in 1997.

The tail of debris that comets leave behind can lead to meteor showers. The Swift-Tuttle comet, for instance, leaves behind debris that interacts with the Earth’s atmosphere to create the annual Perseids meteor shower.

Bright and brilliant

Comet NEOWISE was discovered on March 27, 2020, by NASA’s Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) spacecraft when the comet was streaking towards the Sun. It made its closest approach to the Sun on July 3 and then turned back to make its way towards the outer Solar System.

Its nucleus is about five kilometres in diameter. Its dust tail and gas tail stretch hundreds of thousands to millions of kilometres, and it has water equal to about 13 million Olympic swimming pools. It is currently travelling at 2,31,000 kmph, about twice as fast as the Earth’s movement around the Sun. It orbits the Sun every 600 to 700 years.

The comet is the brightest to be visible from the Northern Hemisphere in about a quarter century. It came closest to the Earth on July 22, at a distance of 103 million kilometres. Astronomers predict that it can be spotted till the end of the month, visible to the naked eye in the Northern Hemisphere — this includes India. It appears as a fuzzy star with a tail. Binoculars and telescopes, naturally, offer a better view.

Keep your eyes on the north-western sky just after sunset. You might just get front row seats to an unforgettable spectacle.

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Printable version | Sep 27, 2020 7:04:23 PM | https://www.thehindu.com/children/a-snowball-in-space/article32193646.ece

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