Christmas Comet Shines in Tandem with Geminid Shower

Comet 46P/Wirtanen, commonly dubbed the ‘Christmas Comet’ thanks to its festive timing, is visible now and will reach its peak brightness on the 16th of December, 2018. Look to the Eastern horizon near the Pleiades cluster as it rises early in the evening.  The comet will be visible all night.  As we near the middle of the month, the green glow surrounding the comet should balloon to approximately twice the apparent size of the Moon making the comet appear as a diaphanous green orb. Head to dark skies to help boost natural night sky contrast and bring a telescope or binoculars for the best views.

For astrophotographers and night sky photographers, 46P-Wirtanen’s arrival with the Geminid meteor shower offers a great opportunity to capture the green comet in tandem with a light show. The nights of the 13th and 14th of December are your best bet when the shower reaches its peak.

Discovered in 1948 by Carl Wirtanen, an astronomer at Lick Observatory in California, 46P has been visible during every pass save one - in 1980 it was too near the Sun to see. This comet is a member of the Jupiter family whose orbits are controlled by the planet and are thought to originate from the Kuiper belt, a massive celestial lagoon of icy masses residing outside of Neptune. Their orbits are relatively short, typically less than 20 years. These are comets that we potentially see pass by Earth often. However, they are not always bright enough to see with the naked eye. Many meet an early demise by striking a planet or breaking apart in the atmosphere of one, such as Shoemaker-Levy 9 famously did in July 1992, or degrading in the intensity of the Sun.

Jupiter family comets are not known for being very bright due to the rapid decline of their structures as they pass through our solar system. Of the over 400 Jupiter family comets known, 46P will be among the brightest to pass near Earth recently and is expected to reach a maximum magnitude of 4.2 at the nucleus as we near the middle of the month. Comet 46P holds the record for the smallest comet nucleus ever recorded.  Measured in 1996 at a likely charitable 1.1km. To give some idea of its size, that’s 1/10th the size of Halley’s comet and 1/13th the size of Hale-Bopp.  While it will not be as bright as a larger comet might have been and may not have much of a visible tail, 46P-Wirtanen is expected to reach a magnitude of 4.2 which is well into the visible-with-the-naked-eye range. This is also the closest the comet is expected to pass near Earth again.

The comet isn’t the only one putting on a show this time of year. The Geminid meteor shower reaches its peak on the 13th and 14th. The most reliably brilliant shower every year, the Geminids put on a unique light display of noticeably slower meteor trails than other showers.  They often seem to skip and glide across the night sky sometimes lasting seconds or leaving behind green dust trails for minutes.  Because Geminid meteors are not the remnants of a typical comet tail but rather the rocky trail of a large mass called 3200 Phaethon, their composition is denser and the result is brighter longer lasting streaks of light as they enter our atmosphere.   This shower can reach peaks frequencies of up to 120 meteor per hour, promising a good showing even from suburban areas with moderate light pollution.  Peak times are about 2am your local time.


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