The Christmas Comet

In the distant past, people were both awed and alarmed by comets, perceiving them as long-haired stars that appeared in the sky unannounced and unpredictably. Chinese astronomers kept extensive records for centuries, including illustrations of characteristic types of comet tails, times of cometary appearances and disappearances, and celestial positions.

These historic comet annals have proven to be a valuable resource for later astronomers.
If we think about an astronomical object connected to an important event in our culture, it is a comet and Christmas 2018 will have its own, real comet!
It is comet 46P/Wirtanen and it could be even visible to the unaided eye!

A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times the Earth's diameter, while the tail may stretch one astronomical unit.

The 2018 pass of Comet 46P Wirtanen is the closest one to the Earth since its discovery 70 years ago, and the closest for the 21st century. In fact, this is the 20th closest known cometary passage near Earth.
Comet Wirtanen is the brightest comet in the night sky now, visible not with the eye alone, but to astronomers with telescopes. In December 2018, comet Wirtanen might indeed become visible to the eye, at least from dark locations. Binoculars should surely show the comet, perhaps by that time with a characteristic comet tail. Wirtanen’s closest approach to the sun will be December 12, 2018, and its closest approach to Earth is just a few days later, on December 16.

46P/Wirtanen was discovered photographically on January 17, 1948, by the American astronomer Carl A. Wirtanen.Due to a limited number of initial observations, it took more than a year to recognize this object as a short-period comet.
46P/Wirtanen is a small short period comet with a current orbital period of 5.4 years. It was the original target for close investigation by the Rosetta spacecraft, planned by the European Space Agency, but an inability to meet the launch window led to Rosetta being sent to 67P/Churyumov–Gerasimenko instead. It belongs to the Jupiter family of comets, all of which have aphelia between 5 and 6 AU. Its diameter is estimated at 1.2 kilometres.

Cyprus Astronomy Organisation is already busy tracking and observing Wirtanen, but expect it to become the subject of some excitement and numerous star parties as it becomes visible to the rest of us in December.

Phedias Hadjicharalambous.
Research Director
Cyprus Astronomy Organisation.

1.Image Credit & Copyright: Alex Cherney