Comets have, in the past, laid question to the very foundation of our ancestors’ knowledge of the cosmos, simply through their sudden appearance in the night sky. The seemingly orderly vastness of the universe, with the backdrop of stars and the wandering planets, suddenly interrupted by an emerging new cosmic wonder, present in some cases as one of the brightest objects in the sky, before fading again to nothing. Comets challenged our primitive views of the universe, and in a way, their observation fuelled forward our deeper understanding of the cosmos.
There are two distinct types of comets that we know of today; short and long period comets. Short period comets tend to have an orbital period of less than 200 years; that is, they will come back towards the inner solar system at least once every 200 years or less. Long period comets, on the other hand, take longer than that to make one complete orbit around the sun. Some comets, on the other hand, will fall towards the inner solar system only once, their path being such that it takes them out of the solar system after their journey inwards.
So what are comets? Essentially, comets are small pieces of rock and ice, coming in towards the centre of the solar system from the outer, farthest reaches of the system.
Originating from the Kuiper belt and the Oort cloud, comets heat up as they approach the inner solar system, resulting in some of their material starting to evaporate, dislodging debris in the process as well. This gives comets their characteristic tail appearance, and the debris stream they leave behind them results in periodic meteor showers, as the Earth always enters the stream of debris left behind by certain comets which crossed its path in the past in the same time of year.
Our most recent encounter with a comet is currently ongoing. Comet 46P/Wirtanen has just ventured towards our inner solar system and made a pass by Earth on December 16. It was visible with binoculars, barely visible to the naked eye, on closest approach, and will remain so for the coming weeks. It is ideal to observe the comet from dark sky locations, using a sky map to locate its updated position as it traverses our skies.
Josef Borg is currently a PhD student within the Institute of Space Sciences and Astronomy, University of Malta, and also the president of the Astronomical Society of Malta.
Did you know?
• The comet Swift-Tuttle is responsible for the Perseid meteor shower. The annual meteor shower, observed by millions around the world, is possibly one of the more famous astronomical events of the year. It is in fact caused by Earth moving through the debris field left behind by comet Swift-Tuttle, and since the Earth always intersects the comet’s path of orbit on August 12-13, we always see the meteor shower during that time of year!
• Comets can hit planets as they careen around the solar system. In 1994, comet Shoemaker Levy 9 made history as it collided into Jupiter, becoming our first observation of a cosmic body hitting another cosmic body other than Earth.
• Most of the brightest comets in the sky in the past were unpredictable until a few months before. While long period comets which have already entered the inner solar system have orbits that are well known, those long period comets still to enter our inner solar system since we started recording such comet observations will remain unpredictable. As such, a bright comet which we knew nothing about due to it being too small and too far away from Earth could suddenly be discovered as it approaches the inner solar system, and another bright comet could be visible unpredictably in a few months’ time!
For more trivia see: www.um.edu.mt/think
Sound bites
Soyuz crew returns to Earth after a memorable 6 months
• Three space station crew members returned to Earth on December 20 after a remarkably eventful stay aboard the orbiting laboratory. Nasa astronaut Serena Auñón-Chancellor, German astronaut Alexander Gerst of the European Space Agency and Russian cosmonaut Sergey Prokopyev safely touched down on the snowy steppe of Kazakhstan at 12:02am EST (0502 GMT), one minute ahead of schedule. The trio spent a total of 197 days in space working as part of Expeditions 56 and 57.
Source: https://www.space.com/42796-soyuz-capsule-lands-space-station-expedition57-crew.html
Geminid meteor shower and Comet 46P dazzle sky watchers
• The Geminid meteor shower of 2018 has lived up to its reputation for being the most spectacular meteor shower of the year, and skywatchers around the world have captured some amazing views of the celestial firework display. To put the icing on the cake, this year sky watchers had the chance to see a bright-green meteor in the night sky. Comet 46P/Wirtanen has been visible to the naked eye all month long, and it was at its brightest when it swung by Earth on Sunday.
Source: https://www.space.com/42785-geminid-meteor-shower-comet-46p-stargazer-photos.html
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