Bengaluru: All through July, people in India and the rest of the northern hemisphere will be able to see the comet C/2020 F3, also known as NEOWISE, in the sky.
Discovered earlier this year, the comet is currently nearly 200 million kilometres from Earth and is bright enough to be seen in the clear dawn sky. However, after around 12-15 July, up until sometime in August, it will be visible at night.
Though bright enough to be seen with the naked eye, in places without clear skies, a pair of basic binoculars will necessary.
NEOWISE was first detected approaching the sun in March this year by the Wide-field Infrared Survey Explorer (WISE) space telescope’s Near-Earth Objects mission. It made its closest approach to the sun on 3 July 2020.
It passed at 44 million kilometres from the sun, even closer than Mercury’s orbit. It has since been gradually approaching the horizon each day, visible lower and lower in the sky. Beyond mid-July, the comet will be visible just after sunset, low in the northwest horizon as it slowly climbs up in the sky through the second half of July.
The comet will make its closest approach to Earth on 22-23 July, passing just over 100 million kilometres from us. That’s over 200 times the distance to the moon, or roughly about the distance from Venus to the sun. Though it is expected to dim over the days as it moves farther from the sun, it will also be more prominently visible against a dark sky.
Comet formation and visibility
The comet’s infrared signature reveals that its nucleus or the main body is about 5km across. The comet is covered with ice and dust, leftover from when it was formed along with our solar system, 4.6 billion years ago.
Comets are made of rock, dust, and ice, and are typically a few meters or kilometres in diameter, but less than 30km. They are thought to form either in the Kuiper belt, beyond Neptune’s orbit, or in the Oort Cloud, billions of kilometres beyond the Kuiper belt in a theorised sphere surrounding the plane of the solar system.
The former kind of comets are called short-period comets and complete an orbit around the sun in less than 200 years. The latter kind are long-period comets that take beyond 200 years.
As passing comets near the sun, the mineral and water ices on them begin to sublimate. Gases and ice escape in a process called outgassing, creating a visible atmosphere, called coma, around it. The coma can actually be larger than the sun in size.
Due to solar wind or the movement of ionised particles from the sun in space, the cometary dust gets dispersed beyond the coma, forming tails that stream out in different directions.
NEOWISE currently has two tails, one that is made of dust and another made of gas.
Because cometary tails are created by the solar wind and radiation from the sun, they always flare out in the direction opposite to the sun, irrespective of the direction of the comet’s orbit. As the comet moves away from the sun, cometary tails lead the nucleus, like they do for NEOWISE today.
While NEOWISE is a bright comet, it will soon likely require binoculars to be seen. Sky gazers and amateur astronomers are waiting for the next ‘great comet’, that will be exceptionally bright and visible for a longer period of time.
While it is estimated that we can see one comet a year with our naked eye, ‘major’ comets like NEOWISE occur on an average of every five to 10 years.
Comet Hale-Bopp was visible for a year and a half in the northern hemisphere in 1995-97 with high brightness, while the Southern Hemisphere saw Comet Lovejoy in 2011-12 for three months.
Second visible comet
Comet Lemmon is currently still visible in the sky at about 10.30pm in the eastern direction. Officially called Comet C/2019 U6, it made its closest approach to the sun on 18 June and has been moving away. However, it takes a pair of binoculars to see this comet.
Comet Lemmon and NEOWISE come on the heels of comets ATLAS (C/2019 Y4) and SWAN (C/2020 F8), both of which fizzed out of visibility. ATLAS broke up in April this year as it moved closer to the sun, likely because of both the sun’s heat and light (as is normal with comets), as well as because of its extreme spin as it flew through the solar system. SWAN started dimming before it even approached Earth on its way to the sun.
NEOWISE will be visible again from Earth in the year 8786, but there will be other comets passing by this year that could potentially brighten.