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Christmas Comet Visits in December

Home > Adelaide > Family | Free | Nature | Outdoor | Unusual Events
by Roy Chambers (subscribe)
Lover of all things interesting and new
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The brightest comic of 2018 is visible in December
A comet named 46P/Wirtanen, but which is being called the Christmas Comet, will make its closest approach to Earth on the evening of December 16 and the morning of December 17 and be the brightest comet of the year. It will be visible to the naked eye from December 14 to 18 but is already visible if you have binoculars or a small telescope. This time also overlaps with the Geminids meteor shower.

Image of a comet courtesy of Soefrm @ Wikimedia
Image of a comet courtesy of Soefrm @ Wikimedia

What is a comet

Comets are often referred to as dirty snowballs. That is, they are big balls of mostly ice, with some dirt and rock thrown in. Comets have an eccentric orbit that will bring them closer to the sun where the heat from the Sun will cause it to heat up and shoot our jets of gas, which form the "tail".

Movies usually show the "tail" of the comet following behind it but in reality, the tail is actually directed at the sun. So it could even be in front of the comet.

Astronomers believe that comets are formed in the outer solar system, where occasionally one will be knocked out of orbit by a collision and fall towards the sun. The most famous comets are periodic comets, which make regular orbits around the sun and will turn up predictably every year.

Up close and personal photograph of a real comet thanks to the European Space Agency
Up close and personal photograph of a real comet thanks to the European Space Agency

Meteor storms are normally caused by the dust trail left behind by a comet. The Geminds meteor shower occurs at the same Comet 46P/Wirtanen is visible this year, but the Geminids are caused by a different comet.

About 46P/Wirtanen

First discovered in 1948 by American astronomer Carl A. Wirtanen, it orbits the sun ever every 5.4 years and is about 1.2 kilometres across. How close a comet comes to the Earth usually changes each time it orbits the sun. This year it will come within 11.6 Millions km of Earth, that is about 30 times the distance of the Earth to the moon. It will be 20 years before it comes this close again.

Spotting 46P/Wirtanen

There is no guarantee that the comet will be visible to the naked eye. Astronomers know where it will it will be and when, but they can't guarantee how bright it will be because that will depend on numerous factors, such as the size of the tail and how much sunlight it reflects. However, it should be visible from December 14 to the 18th and the best bet of seeing it will be on the evening of the 16th through to the morning of the 17th.

Some comets just look like fuzzy blobs as in this photo courtesy of NASA & ESA
Some comets just look like fuzzy blobs as in this photo courtesy of NASA & ESA

If you have a telescope or binoculars, you should take them with you. In fact, you should be able to spot it already using these.

Even at its brightest, it may not be visible in urban or suburban environments with the naked eye, depending on how much light pollution is around. It will be better to get out of town, especially if you are going to go shooting star spotting at the same time.

In Australia, it should be visible all night from after twilight and until just before dawn. During the peaking viewing days, it should be in the constellation Taurus near the Pleiades star cluster.

If you are not confident about looking for constellations, you can also find the location using the star map or an astronomy app on your phone. I use Sky Map but it is just one of many great apps that do the same thing. These apps should show the exact location of the comet and you can point your phone at the sky and it will show you what you are looking at, naming the various astronomical bodies and features.

First of all, you want to adjust your eyes to night conditions. So once you have found Taurus and the Pleiades star cluster, turn off your phone, camera screen, smartwatch, flashlight and so on and let your eyes adjust for about 20 minutes.

What you are looking for is a hazy elongated blob. If you are lucky you will see the classic comet shape with a tail, which does look awesome. But it will depend on how bright the comet actually is. This is why having binoculars can come in handy. If you are unlucky, all you will see is that hazy blob.

Times and elevations around Australia

The following dates are for the evening of the 16th and morning of the 17th. Note: it is recommended that you wait until after astronomical twilight. Just to make things confusing, there is the regular or civil twilight, nautical twilight and astronomical twilight, which occur in that order. Basically twilight is the time between sunset and dusk (or dawn and sunrise) when the sky is still light. Astronomical twilight is longer because astronomers need to wait until the sky is completely dark, not just very dark, to observe very faint objects in the sky.

Also note, on December 16 there is a waxing half moon, which will not set until after midnight, interfering with the visibility of the comet. So you may need to stay up late to really see the comet.

In Brisbane the comet it will rise above the horizon on 4:51 pm, but you won't really see it until later with astronomic twilight being after 8 pm and the comet should be at its brightest at around 10 pm when it will be 40 degrees above the horizon. One complication is that the waxing half moon doesn't set until 12:44 am on the 17th, so it is better to wait until after then.

Once again viewing times in Sydney for the comet fall after astronomical dusk and astronomical dawn, which are from 9:46 pm until 3:54 am with the moon setting at 1:52 am, so you have a few hours of good viewing. If the moon is not causing too much light pollution, then the best time is at 11:12 pm.

In Melbourne full dark is between 10:43 to 3:57 am and the moon sets at 2:18 am. If it wasn't for the moon, the best time would be 11:37 pm, but you may have to stay up later to wait for the moon to set.

Adelaide is similar to Melbourne, with the moon setting at 2:14 am and astronomical twilight ending at 10:12 pm to 4:09 am. You might try viewing the comet form 11:33 pm, though I think you will have to stay out until after the moon sets for the clearest view.

Luckily in Perth, things are a little earlier. Astronomical dusk is from 9 pm and astronomical dawn is at 3:25 am. The comet will be at its best from 10:35 pm with the moon setting at 1:16 am.
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Why? See a visitor from the outer solar system fly by
Where: Visible to the naked eye in the constellation Taurus
Your Comment
Could you clarify please - your article states that the tail is pointed toward the sun, whereas all research we have found on line says it points AWAY from the sun. My husband has said he has ALWAYS known that and then the argument began lol.
by esote (score: 1|12) 769 days ago
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