Comet C/2020 F3 NEOWISE, discovered only last March, has graced our skies for the past month, with observers in the Northern hemisphere making the most of this rare opportunity with a myriad of different photos and naked eye observations of the cosmic wanderer.

Observers from Malta could easily observe the comet, first in the morning skies towards the northeast and then in the evening skies towards the northwest. Even now, the comet is still visible in the northwestern skies after sunset, albeit the comet has now gotten considerably fainter.

Comets are pieces of rock and ice originating from the outer edges of the solar system. Depending on the time they take to make one complete orbit around the sun, the extent of this orbit can be fully estimated. Shorter-period comets, with orbital periods of up to 200 years, normally origi­nate from the Kuiper belt, just beyond the planet Neptune.

Halley’s comet is one famous example of such a short-period comet. Longer-period comets, with orbital periods longer than 200 years, tend to originate even further out, from the scattered disk or the Oort cloud, in the farthest reaches of the solar system.

Comet C/2020 F3 NEOWISE is one such example of a long-period comet, with the currently estimated orbital period being 6,766 years.

The most distinguishing feature of comets is their tails. Comets typically have a dust and ion tail, which are at angles from each other, as the comet heats up as it approaches the inner solar system in its highly eccentric orbit, thus getting close to the sun.

Both tails point in the opposite direction from the sun, but the ion tail points more directly away from the sun, in the direction of the solar wind. The ion tail is composed of ionised gases, evaporated from the surface of the comet, while the dust tail is composed of dislodged small particles pushed outward by solar radiation, due to radiation pressure.

These heavier dust particles start to fall in orbit around the sun themselves as they are affected by the sun’s gravity, resulting in a curved appearance to the dust tail. This can be clearly seen in images of our most recent bright comet.

Bright comets tend to be, for the most part, rather unpredictable. The last very bright comet visible from the Northern hemisphere was Comet Hale-Bopp in 1997. With an estimated orbital period of around 2,500 years, comet Hale-Bopp was also a long period comet. Although we will have to wait even longer than that for a return of Comet C/2020 F3 NEOWISE to the inner solar system, we can expect a number of other long period comets, still as yet undiscovered, arriving in our neighbourhood in the near future.

Mr Josef Borg is a PhD student at the Institute of Space Sciences and Astronomy of the University of Malta, and also president of the Astronomi­cal Society of Malta.

Did you know?

• Halley’s Comet next pass will be in 2061. Comet 1P/Halley is a short-period comet, with an orbital period of 76 years. The comet last passed by the Earth in 1986, which was actually an unfavourable pass when compared to other previous passes. The comet is expected to be significantly brighter on its next pass in 2061.

• Comet passes are the reason behind most periodic meteor showers. As comets approach the inner solar system, normally at a significant angle from the orbits of the planets along the ecliptic, they will intersect this plane of orbits at a particular point. If that point happens to be close to the Earth’s own orbital path, they will leave behind a string of dust particles in their wake in the Earth’s orbit. As a result, whenever the Earth crosses this particular point in its orbit, it will collide with these small particles, which we see as meteors burning up in our atmosphere.

• Several comets are visible in our skies right now Although bright comets like Comet C/2020 F3 NEOWISE are rare, there are normally several less bright comets present in our skies all the time. Even right now, there are seve­ral comets, each of a different brightness, which can be seen even with a moderately-sized telescope.

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https://www.space.com/mars-atmosphere-gas-detections-methane-mystery.html

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For more soundbites listen to Radio Mocha every Saturday at 7.30pm on Radju Malta and the following Monday at 9pm on Radju Malta 2 www.fb.com/RadioMochaMalta/

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