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Heads up! Bright Comet Wirtanen flies by Earth on Sunday

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Scott Sutherland

Meteorologist/Science Writer

Sunday, December 16, 2018, 1:59 PM - Fall skywatchers have been treated to a string of meteor showers this season, culminating in the 'rock comet' Geminids, but watch out on Sunday, as a bright comet flies by Earth!

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Quick List:

• Sept 24 - The Harvest Moon

• Oct 8 - Draconid Meteor Shower

• Oct 20 - International Observe the Moon Night

• Mid-Oct - The Zodiacal Light in the East, before dawn

• Oct 21-22 - Orionid Meteor Shower

• Nov 5-6 - Taurid Meteor Showers

• Nov 17-18 - Leonid Meteor Shower

• Dec 13-14 - Geminid Meteor Shower

• Dec 16 - Closest approach of bright Comet Wirtanen!

WHAT'S ON DECK?

Close approach of bright Comet 46P/Wirtanen - Dec 16

It's been quite awhile since we've had a good naked-eye visible comet swing past Earth. Comet ISON was the last one to show promise, back in 2013, but it fizzled as it was vapourized by the intense heat of the Sun.

Now, Comet 46P/Wirtanen is putting on a show for us in mid-December, and it has the potential to become even better!



46P/Wirtanen, captured on December 12, 2018, using a backyard telescope and DSLR camera. Credit: Stub Mandrel (CC BY-SA 4.0)

Discovered in 1948, by astronomer Carl A. Wirtanen, this comet is a Jupiter-family comet - a group of short-orbit comets (with periods of less than 20 years), whose orbits extend out about as far as Jupiter, before they fall back towards the Sun.

46P/Wirtanen takes roughly five and a half years to go around the Sun once, so it has made around a dozen orbits since its discovery, but this one is remarkable because it is making its closest pass by Earth in recorded history.

On December 16, the comet will reach a distance of about 11.5 million kilometres from Earth, roughly 4 days after it makes its closest pass around the Sun (perihelion). That means that the comet will be nearly at its brightest.



Comet Wirtanen's flyby of Earth on December 16, 2018, will be the 10th closest comet flyby in history. Credit: Celestia/Scott Sutherland

How bright will that be?

A comet of this size - fairly small at around 1 km wide - would come in at around magnitude 8 at that time. It would need to reach at least magnitude 6 to be visible with the naked eye in dark skies (in rural areas, far from the light pollution of cities).

According to the University of Maryland's Comet Wirtanen Observing Campaign, however, Wirtanen is a "hyperactive comet". This means that it produces far more water than is expected from a comet of its size. Thus, the comet's extra icy coma and tail shine brighter than they normally would.

Based on this, Comet Wirtanen could be as bright as magnitude 3 as it swings past Earth - bright enough to be visible with the naked eye, even from under the dome of light pollution from a major city!

(Remember: the lower an object's magnitude, the brighter the object is. The Full Moon is around -13. Venus, at its maximum brightness, is -5. Sirius, the brightest star in our sky, is -1. Vega, the standard for the system, is magnitude 0. The limit for what we can see from the core of a light polluted city, is about magnitude 3 (enough to see the inner planets, Jupiter and the brightest stars, such as Polaris, Antares, Aldebaran, Betelgeuse, Rigel, Capella, Vega, Arcturus and Sirius.)



The position of Comet Wirtanen in the sky, at 8 p.m. local time, on the night of December 16, 2018, with respect to the constellations. Credit: Stellarium/Scott Sutherland

As of December 12, the Comet Wirtanen Observing Campaign was reporting that the comet made its closest pass around the Sun (perihelion), and it had reached magnitude 4 (or even slightly brighter).

This puts the comet right on track for its predicted brightness, so get ready over this weekend to check it out!

Update (Dec 16): One complication to viewing Wirtanen, according to the Observing Campaign website, is that, even if it reaches its predicted magnitude of 3, with such a wide coma (atmosphere of dust and gas) around the comet, Wirtanen will be harder to pick out in the sky, compared to a bright point of light (such as a star, planet or asteroid) that was of the same brightness. The light pollution of cities will make picking out the difference between black space and comet coma even more difficult.

For the best experience, find somewhere outside of city light pollution, and give your eyes time to adjust to the dark (about 30 minutes should be good). Avoid any bright sources of light, including your cellphone screen, during this time. Bring along some binoculars, or a telescope, if you can, just in case.

To find the comet, look for the Orion Constellation, then turn your gaze upward from there, to find the Pleiades cluster (a small 'blob' of brightness in the sky). Wirtanen will be nearby there on Sunday night.





WHAT WE'VE ALREADY SEEN

Harvest Moon 2018

The first Full Moon of Fall 2018 was the Harvest Moon, which occurred around 11 p.m. ET, on the night of September 24.



The Harvest Moon, from NASA's animation showing the moon, every hour of every day, for all of 2018. Credit: NASA's Goddard Scientific Visualization Studio

This particular Full Moon is a favourite for skywatchers, not only for viewing, but taking photographs. If you snapped any photos, yourself, you can upload them into our gallery for everyone to see!

Draconid Meteor Shower - Oct 8

The first meteor shower of Fall 2018 was the Draconids.

The Draconids are usually a fairly minor shower, delivering about 10 meteors per hour, max. This year, however, there are prime viewing conditions, at least from an astronomical perspective. The Moon, which can provide enough light in the sky to spoil a minor shower like this one, will only be a thin sliver visible just at sunset, so the sky will be left clear of any extra light for the rest of the night.

In addition, this year there was a rare meteor outburst from the Draconids, first predicted by researchers at Western University. This meant that, just for a brief period on the night of October 8-9, some observers were able to see MANY more meteors than usual - around 100-150 per hour seen, with estimates of several hundred per hour, once all the data has been compiled from different observers. While Earth was experiencing this outburst, the meteor stream at Lagrange Point 2, roughly 1.5 million kilometres away, on the opposite side of the Earth from the Sun, was supposed to be much more concentrated. With the Gaia Telescope - the spacecraft that has been delivering highly precise maps of our galaxy - currently stationed at L2, it reportedly shut down for the duration of the event, turning its hardened side to the flow of meteoroids, to protect its sensitive instruments.

Orionid Meteor Shower - Oct 21-22



The radiant of the Orionid meteor shower, after midnight on the nights of Oct 21-22. Credit: Stellarium/Scott Sutherland

The Orionid meteor shower is the second meteor shower of the fall season, and the second of the year that originates from Halley's Comet (the first is the eta Aquariids in April/May). The Orionids begin on October 2 and run until November 7, each year, but the best time to watch this meteor shower is during its peak, on the night of October 21-22.

This particular meteor shower is only a moderate one, delivering around 20 meteors per hour under ideal conditions. One great thing about the Orionids, however, is that the meteors can be quite bright!

As one example, here is an Orionid meteor that was spotted by the University of Toronto Scarborough Observatory's all-sky camera on the night of October 18, 2017 at around 11:11 p.m. ET (3:11 UTC 19 Oct).

The #UTSC meteor camera just captured this video. Note: automated tweet of unverified raw data, might not be a #meteor. ???? pic.twitter.com/VJzu2EDpCN — UTSC Observatory (@UTSCObservatory) October 19, 2017







Three views of this bright Orionid meteor, taken from three different all-sky cameras in Ontario. Click or tap the image to see more info on this meteor. Credit: UTSC Observatory/Western Meteor Group

The Zodiacal light - mid-to-late October



Moonlight and zodiacal light over La Silla. Credit: ESO

This fall, skywatchers will have a chance to see the immense cloud of interplanetary dust that encircles the Sun, which manifests in our night sky as "The Zodiacal Light".

In the Royal Astronomical Society of Canada's 2018 Observer's Handbook, Dr. Roy Bishop, Emeritus Professor of Physics from Acadia University, wrote:

The zodiacal light appears as a huge, softly radiant pyramid of white light with its base near the horizon, and its axis centred on the zodiac (or better, the ecliptic). In its brightest parts, it exceeds the luminance of the central Milky Way.

According to Dr. Bishop, event though this phenomenon can be quite bright, it can easily be spoiled by moonlight, haze or light pollution. Also, since it is best viewed just after twilight, the inexperienced sometimes confused it for twilight, and thus miss out.

On clear mornings, and under dark skies, look to the eastern horizon, in the hour to half an hour just before twilight begins at dawn, from about October 13-27.

Taurid Meteor Showers - Nov 5-6 & 12-13

The Taurids are a strange one, when it comes to meteor showers.

It's actually two meteor showers - the Northern Taurids and the Southern Taurids - that originate from two separate objects (Asteroid 2004 TG10 for the northern stream and Comet Encke for the southern), which overlap into one shower, with two different peaks.



The radiants of the two Taurid meteor showers, on the night of Nov 8, roughly midway between the two peaks. Credit: Stellarium/Scott Sutherland

The meteors produced by these showers tend to be slower than most, taking their time crossing the sky. Also, there can be pebble-sized bits in the stream that produce extremely bright bolides - meteors that flare brightly as the meteoroid that produces them explodes due to internal pressures!

Even with the two combined meteoroid streams from these objects, these meteor showers still do not produce many meteors, with perhaps 5-10 per hour showing up during each of the two peaks. So, if you try your luck at this one, you will need to be patient.

Fortunately, the nearly New Moon will give excellent viewing conditions on the night of November 5-6, and the crescent Moon on the night of November 12-13 will set at around 9 p.m., local time, so it won't offer up much competition in the sky.

Leonid Meteor Shower - Nov 17-18



The radiant of the Leonid meteor shower, after midnight on the night of Nov 17-18. Credit: Stellarium/Scott Sutherland

From November 6-30, each year, Earth sweeps through a stream of debris left behind by Comet Tempel-Tuttle.

As we get deeper into the stream, the number of meteors seen in the sky increases, and reaches a peak on the night of the 17th. As all of these meteors can be traced back to a point of origin in the sky that's inside the constellation Leo, this is called the Leonid meteor shower.

Unlike most other meteoroid streams, which contain only minuscule bits of dust and ice, the stream for the Leonids also contains many gravel-sized bits. When these pebbles hit Earth's atmosphere, they produce very bright meteors in the night sky, known as fireballs.

This shower tends to be a fairly minor one, overall, producing around 15 meteors per hour, on average.

On occasion, however, usually shortly after Comet Tempel-Tuttle makes a pass around the Sun, the Leonids can deliver a meteor storm, with hundreds of meteors streaking through the sky every hour. According to NASA, one such storm, on the night of November 12-13, 1833, reportedly delivered an estimated 240,000 meteors over a 9-hour period!

According to experts, such a storm is not expected again until 2033 or 2034.

Since the Moon is more than half full at the time of the shower peak, there will be some competing light in the sky, which will wash out the faintest meteors.

It will definitely be worth it to get out to see the brightest of them, though!

Geminid Meteor Shower - Dec 13-14

The August Perseid meteor shower is often held up as the best meteor shower of the year, but the Geminids are definitely a contender, and in 2018, they promise to put on an amazing show!



The radiant of the Geminid meteor shower, after midnight on the night of Dec 13-14. Credit: Stellarium/Scott Sutherland

Not only do the Geminids deliver more meteors than pretty much any other meteor shower - up to a maximum of 120 per hour when it peaks on the night of December 13-14 - this year there are great conditions for seeing them! The waxing crescent Moon will set fairly early in the evening, so much of the night will be free of the Moon's light, allowing us the potential to see more of the dimmer meteors from this shower.

This year, the average viewer, under clear, dark skies, can expect to see from 60-80 meteors per hour, possibly up to 100 under ideal conditions (clear sky, dry conditions, far from civilization, and with a clear view to every horizon). The closer you are to sources of light pollution, however, the fewer meteors you will see. Read on for more details.

One of the remarkable things about the Geminid meteor shower is that it originates from a rare object, 3200 Phaethon - a so-called 'rock comet'.

WHAT IS A ROCK COMET?

Normal comets are massive lumps of ice, mixed with dirt and rock, that are left over from the formation of the solar system. As they loop around the Sun, the heat causes them to throw off a similar combination of ice, dust and rock, which is left in a debris stream behind the comet, and this debris stream follows along roughly in the same orbit as the comet. When Earth encounters one of these debris streams, the ice, dust and rock particles produce streaks across the sky that we call meteors.

A rock comet, on the other hand, is an asteroid - a huge chunk of rock, with maybe a little bit of ice clinging to it - that follows an orbit very similar to that of a comet. When it loops around the Sun, the heat blasts mainly rock and dust off its surface, which is left behind in the same kind of debris stream we see from a normal comet. Since the rock and dust particles are more 'durable' kinds of meteoroids than the ice, they tend to produce brighter and more long-lasting meteors.

According to NASA's Bill Cooke, who heads up the agency's Meteoroid Environments Office, another object - Apollo asteroid 2005 UD - has an orbit very similar to Phaethon, and so it may be related to the Geminids, as well. Possibly, Phaethon and 2005 UD may have been part of the same larger object, in the distant past, and their orbit (and the debris stream), was produced by a collision.

Regardless of the origin of the debris stream, its rocky contents are what makes Geminid meteors so bright. As an added bonus, since those rocky remnants are packed with minerals and metals, Geminid meteors tend to be multi-coloured! As the meteoroids slam into the upper atmosphere, travelling at around 130,000 km/h, they vapourize, producing colours like yellow (from iron), blue and green (from magnesium), and even red (by ionizing atmospheric oxygen and nitrogen molecules).

With the meteor shower scheduled to reach its peak on the morning of the 14th, the hours after midnight and the pre-dawn hours were likely the best for watching this show!

Watch below as Science@NASA tells us about how the International Space Station will be observing this meteor shower along with us.





HOW TO WATCH METEOR SHOWERS

The first thing to consider when planning to watch a meteor shower is to keep track of the weather.

Be sure to check The Weather Network on TV, on our website, or from our app, just to be sure that you have the most up-to-date forecast.

Next, you need to get away from city lights, and the farther away you can get, the better.

Watch below: What light pollution is doing to city views of the Milky Way





For most regions of Canada, getting out from under light pollution is simply a matter of driving outside of your city, town or village. Some areas, though, such as southwestern and central Ontario, and along the St Lawrence River, the concentration of light pollution is very high. Getting far enough outside of one city to escape its light pollution, unfortunately, tends to put you under the light pollution of the next city over. In these areas, there are dark sky preserves, however a skywatcher's best bet for dark skies is usually to drive north.

Once you've verified you'll have clear skies, and you've escaped from urban light pollution, stop somewhere safe and dark (provincial parks, even if you're confined to the parking lot, are usually an excellent location).

For best viewing, it's crucial that you give your eyes time to adapt to the dark. Between 30-45 minutes is optimal.

During that time, avoid all bright sources of light, including your cellphone screen. If you need to use your cellphone during this time, consider lowering the amount of blue light your screen gives off and reduce its brightness. Also, look into an app that puts your phone into "night mode", which shifts the screen colours even more into the red. Once you've done that, checking your phone while skywatching will not have as big an impact on your nightvision.

Note: Although the graphics presented here point out the location of the meteor shower 'radiants' - the point in the sky where the meteors appear to originate from - the meteors themselves can show up anywhere in the sky. So, the best way to watch a meteor shower is to look straight up. That way, your field of view takes in as much of the sky as possible, all at once. Bring a blanket to spread on the ground, or a lawn chair to sit in, or even lean back against your car.

Bringing along some family and friends is also great, since it's best to share these experiences with others.

SPECIAL NOTE: When you see times listed for the peak of a meteor shower, don't worry about time zones. The stream of meteoroids Earth passes through during a shower is MILLIONS of kilometres wide, so the shower lasts for days and the peak tends to last an entire night (some, like the Quadrantids, are notably shorter). When observing a shower, it begins for any particular observer when their location on Earth rotates into the oncoming stream particles (typically when night falls, or about an hour before the radiant rises above the horizon). It reaches its local peak when the incoming particles are coming in directly overhead, or as close to that as possible (this is the "Zenith Hourly Rate" or ZHR that you will see associated with meteor showers).

Sources: IMO | Royal Astronomical Society of Canada | Western University | University of Maryland | International Meteor Organization | NASA

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