Follow Comet Wirtanen

Comet Wirtanen / 46P on December 6, 2018

A well-known comet is making its closest approach to Earth in many years and promises a good show. 

Comet Wirtanen is now climbing up the late autumn and winter sky for northern hemisphere viewers, and is already a fine binocular comet. By mid-December it might be bright enough to be visible to the naked eye, but only from a dark rural site.

Discovered in 1948 by Carl Wirtanen at the Lick Observatory, his namesake comet orbits the Sun every 5.4 years. So unlike other recent bright comets that have visited us for the first time, Comet Wirtanen (aka 46P) is well known. It is one of many “Jupiter-family” comets whose orbits have been shaped by the gravity of Jupiter and orbit the Sun about every 6 years.

So since it was discovered, Comet 46P (the 46th comet in the catalog of periodic comets) has been well observed. It isn’t better known because at most returns it never gets bright, and that’s because it never gets closer to the Sun than a little more than the distance from the Earth to the Sun. (Its perihelion distance is 1.06 AU, with 1 AU, or Astronomical Unit, being the average distance from Earth to the Sun.)

However, despite this, we’re expecting – indeed already enjoying – a good show at this return.

Due to the quirk of orbital clockwork, on this return the comet reaches its closest point to the Sun just before it is also closest to Earth.

That puts the comet “just” 11,680,000 kilometres from us at its closest approach to Earth on December 16, four days after perihelion, the point when the comet is closest to the Sun.

Comet Wirtanen from Space
The relative position of the Sun, Earth and Comet Wirtanen on December 16, 2018.

Comet Wirtanen will be relatively bright simply by virtue of its proximity.

But it is also an active comet, emitting a lot of gas and dust into a large “coma,” and that’s what we see, not the 1-kilometre-wide icy nucleus itself which is too small and shrouded by the coma. (As a footnote, Comet Wirtanen was to have been the comet that the European Rosetta probe was to visit, but launch delays forced ESA to switch cometary targets.)

Comet Wirtanen is glowing at magnitude 5 to 6, technically making it visible to the naked eye. However, because it is large and diffuse, in practice you need binoculars to see it – now.

But as it approaches Earth and the Sun, Wirtanen will brighten, perhaps to magnitude 3 (the brightest stars are magnitude 0 to 1), making it easier to see with the unaided eye from a dark site.

The one catch is that as it heads toward its brightest in mid-December the waxing Moon also begins to enter the sky and wash out the comet with moonlight.

The first two weeks of December will be prime time for Wirtanen

Comet Wirtanen Path
The path of Comet Wirtanen across the sky in December 2018. The yellow dots mark the position of the comet at nightly intervals for late evening (10 p.m.) for North America. While comet will be in the sky most of the night, it will be highest in late evening about 10 p.m. local time when the sky will look as depicted, with the comet high in the south to southeast. Click or tap to download a full-sized version.

The first two weeks of December will be prime time for Wirtanen, with a particularly good opportunity coming on the evenings of December 15 and 16 when it shines below the Pleiades star cluster. The gibbous Moon will set about 1 to 2 a.m. with the comet still high enough for a dark sky view and photos.

Those will be great nights to shoot the comet and the cluster with a telephoto lens, provided the camera is on a tracker for untrailed exposures of 1 to 4 minutes. A 135mm to 300mm lens will frame the pair well.

Winter Green Comet with Orion
Comet Wirtanen as a green glow at upper right here in Eridanus. and well to the west of Orion, rising here at left, on the evening of December 6, 2018. I shot this with a wide-angle 35mm lens in a blend of tracked and untracked 1-minute exposures.

After that, through late December, the bright Moon will interfere with  the view. For example, a close approach of the comet near the star Capella on December 23 happens with the nearly Full Moon not far away.

Comet Wirtanen / 46P on December 6, 2018
Comet Wirtanen in a close-up through a telescope on December 6, 2018 in a stack of short and long exposures.

I took the above close-up photo of Comet Wirtanen on December 6. It is a long-exposure telescopic view, but the comet is easy to see with binoculars. It appears visually and photographically as a diffuse fuzzball, with the camera recording a vivid cyan colour from glowing cyanogen and diatomic carbon molecules. You won’t see that colour with your eyes, even in a telescope.

Comet Wirtanen Path Dec 8 to 16
The path of Comet Wirtanen Dec 8 to 16 superimposed on an actual sky image with the comet taken December 8. The circle indicates the field of view of typical binoculars. On Dec 15 and 16 the comet will be in the same binocular field as the Pleiades star cluster. The positions are for about 10 pm Mountain Standard Time for each of those dates.

Even at the comet’s best in mid-December any tail might be hard to see and even photograph (it appears faintly above) as it will be both faint and pointed directly away from us because, as comet tails do, it will also be pointed away from the Sun.

Look for a large glow which will be grey to the eye but green to the camera.

While you can just take pictures for yourself, astronomers are asking amateur astrophotographers to participate in a worldwide observing campaign to monitor Comet Wirtanen. More details are available here at and at

Clear skies and happy comet hunting!

— Alan, November 30, 2018 (Revised December 6) / © 2018 Alan Dyer / 

New Year’s Eve Sky: Aurora, Orion, and a Comet

New Year's Eve Winter Sky

The New Year’s sky was filled with Northern Lights, a panorama of stars, and a comet at dawn.

It was a busy night for stargazing as 2015 turned to 2016. A fine display of Northern Lights kicked off the celebrations, as curtains danced in the east as Orion rose (below).

New Year's Eve Aurora, Dec. 31, 2015

Toward midnight the Lights kicked up again, now with Jupiter (on the horizon) and Leo rising in the east (below).

New Year's Eve Aurora #2 (Dec 31, 2015)

I shot hundreds of frames for time-lapse sequences, and assembled them into a short music video. Click on the buttons to enlarge it to HD.



Just before midnight, while the second time-lapse was going and the aurora was still active, but before the Last Quarter Moon rose to light the sky, I shot a set of tracked images taking in the entire winter sky from horizon to well past the zenith.

That image is at top. It takes in the winter sky and northern winter Milky Way,  from Canis Major just above the horizon, up past Orion, then on up to Perseus and Cassiopeia at top right.

It shows how Orion and Sirius, the night sky’s brightest star, stand nearly due south at midnight on New Year’s Eve.


Comet Catalina near Arcturus on New Year's Day
Comet Catalina (C/2013 US10) near Arcturus in the constellation of Bootes, at pre-dawn on the morning of January 1, 2016, with the Last Quarter Moon nearby illluminating the sky. A long, faint ion tail is visible extending 2 to 3 degrees to the right while a brighter but stubby dust tail extends down to the south. Shot from home using the 200mm Canon telephoto and 1.4x extender at f/4.5 for a stack of 8 x 2-minute exposures at ISO 800 with the Canon 6D. Median combined stacked to eliminate satellite trails. The comet is slightly blurred due to its own motion in that time.
The final show of the night, now before dawn on New Year’s Day 2016, was Comet Catalina sitting right next to the bright spring star Arcturus. The comet was visible in the moonlight as a fuzzy object next to brilliant Arcturus, but the photo begins to show its faint tails, just standing out in the moonlit sky.

The comet will become more visible later this month once the waning Moon exits the dawn sky, as Catalina is expected to remain a nice binocular comet for most of the month as it heads high into northern sky.

Happy New Year to all! Have a celestial 2016!


Don’t forget, you can download my free 2016 Sky Calendar as a PDF. See my previous blog for details and the link. 

— Alan, January 1, 2016 / © 2016 Alan Dyer / amazing

Venus and the Comet

Comet Catalina near Venus (Dec 9, 2015)

Comet Catalina sports two tails as it moves past Venus in the dawn sky.

This was the view this morning, December 9, from my site in Arizona, of Comet Catalina near Venus in the dawn sky. This is a telephoto lens shot that provides a view similar in size to what binoculars show.

However, the blue ion tail visible here stretching back several degrees is mostly a photographic target. Visually, just Catalina’s short, stubby dust tail at lower right is obvious.

The ion tail points away from the Sun, while the dust tail extends along the comet’s orbit, showing where the comet has been.

The view, both visually and photographically, of the comet will improve as it climbs higher into the eastern morning sky and as it moves away from the glare of Venus. The Moon is also now gone from the dawn, at least for the next couple of weeks.

The comet is dimmer than expected but should at least maintain this brightness for the next month or so.


This is a stack of 5 x 90-second exposures, taken with the 135mm telephoto and 1.4x extender for a focal length of 190mm, at f/2.8 and with the Canon 5D MkII at ISO 1600, tracked on the iOptron Sky-Tracker. Two other exposures, of 15s and 1s, were blended in with luminosity masks to reduce the glare of Venus to a smaller size.

— Alan, December 9, 2015 / © 2015 Alan Dyer /

Capturing Comet Catalina

Comet Catalina with Venus at Dawn

I got the comet but it isn’t what was hoped for – a faint fuzzball in binoculars.

This was Comet Catalina (aka C/2013 US10) in the dawn sky this morning, December 6, with the comet appearing as a fuzzy star below brilliant Venus in binoculars, and just revealing its two short tails in photos. It’s the cyan-colored object near the centre. Venus is the brilliant object.

This image is with a telephoto lens, and covers a little more of the sky than typical binoculars would show. I knew this would be a binocular comet at best, but it’s barely that. This is more a comet for telescopes.

But as the Moon departs the scene and the comet climbs higher the view may improve. Still, if you are pining for views of Comet Catalina and are stuck under cloudy winter skies at home, don’t be worried. You aren’t missing too much. Except …

Arch of the Autumn Milky Way
The arch of the Milky Way in the northern autumn and early winter sky, from Arizona on December 5, 2015. The Milky Way extends from Aquila to the left, in the southwest to Cassiopeia at top right, to Perseus and Auriga at far right, in the northeast. I shot this from the Quailway Cottage near Portal, Arizona, latitude +32° N. The view is looking north toward the celestial pole. Polaris is just right of lower centre. This is a stack of 8 tracked exposures, each 3 minutes at f/2.8 with the 15mm lens and Canon 6D at ISO 1600, with the ground coming from one exposure to minimize blurring. The camera was on the iOptron Sky-Tracker.

This was the view of the autumn Milky Way from here in Arizona last night. Pretty impressive under nearly perfect sky conditions. And then there’s this …

Winter Sky Setting over the Chiricahuas
Orion and the northern winter constellations and Milky Way setting at dawn over the Chiricahua Mountains of southwest Arizona, near Portal, AZ. The waning crescent Moon in the west provided the illumination in this dawn shot from December 6, 2015. Orion is just above the main peak at centre, with Sirius, in Canis Major, to the left and Aldebaran, in Taurus, to the right. The Pleiades are setting at right. The star cluster at top is the Beehive, M44, in Cancer. Bands of airglow add the red streaks. The site is the Quailway Cottage near Portal, Arizona. This is a stack of 4 x 2 minute exposures, tracked, at f/3.5 with the 15mm full-frame fish-eye lens and Canon 6D at ISO 1250, for the sky, and the same specs for 4 exposures, untracked for the ground. Each set was mean-combined stacked to reduce noise.

This was the winter Milky Way with Orion setting into the west over the Chiricahuas at dawn. Turn around from looking at the comet and this was the view. So who cares if the comet isn’t too great? There’s lots more to see and shoot. With no snow, no frost, no dew.

More to come this week I trust!

— Alan, December 6, 2015 / © 2015 Alan Dyer /

Heads Up! – A Comet in the December Dawn

Dec 7 Venus & Moon

A new comet is coming into our morning sky, for our binocular viewing pleasure.

Comet Catalina, aka C/2013 US10, has emerged from behind the Sun and is beginning to rise into our northern hemisphere dawn sky. The new comet promises to be visible in binoculars, but likely won’t be obvious to the unaided eyes.

On the morning of December 7 the comet sits within a binocular field of the waning crescent Moon which itself sits just above brilliant Venus. That in itself will be a remarkable view, best appreciated in binoculars, and a fine photogenic sight for the camera.

The close conjunction of the crescent Moon with Venus alone will be enough of an attraction on December 7, but the comet should add to the scene.

December 7 Venus Occultation

Even more, later in the day the Moon actually passes in front of, or “occults,” Venus in the daytime sky for most of North America.

That occultation happens in the morning for western North America and in the early afternoon for eastern North America. However, you’ll need a telescope to see it well, and very clear blue skies.

Stellarium Occultation

Use planetarium software (the free Stellarium program, for example, shown above, if you do not own astronomy software) to simulate the sky and provide the occultation times for your location. Zoom into the Moon and run time back and forth on December 7 to see when Venus goes behind the Moon and reappears. The screen shot above is for Calgary.

Back to the Comet

Comet Catalina was discovered in October 2013 at the Catalina Observatory in Arizona. The comet spent the last few months in the southern hemisphere sky, but is now coming north and into our sky, but at dawn.

Comet Catalina Path

It rises higher and higher each morning  through December and into the new year. It may remain at fifth magnitude, bright enough to be easily visible in binoculars from a dark site, but likely not naked eye.

The chart above plots the comet at daily intervals, from December 4 to January 1. The comet is shown for December 15. Note that on the morning of January 1 it sits within a telescope field of the bright star Arcturus.

The distance from Earth to the comet decreases through December and early January, keeping the comet at a constant brightness even as it recedes from the Sun. We are closest to Catalina on January 17, at a far distance of 108 million km. But in late January the comet fades rapidly to become a telescope target.

To see Comet Catalina this month, get up 1 to 2 hours before sunrise and look southeast to east. But you will need dark skies to see it well. This will not be a good urban comet.

Nevertheless, as far as we know, this will be the best comet of 2016.

— Alan, December 2, 2015 / © 2015 Alan Dyer /


Catching A Comet

Comet Lovejoy Through a Telescope

Tonight I caught a close-up of the green head and blue tail of Comet Lovejoy.

Clear skies tonight, Tuesday, January 6, allowed me to shoot Comet Lovejoy from home using a telescope and guiding system for a close-up view. I had just over half an hour of darkness between end of twilight at 6:30 and moonrise at 7:15 but that’s all I needed to grab several guided exposures.

This telescopic shot takes in a field of about 5 by 3 degrees, a little smaller than what most binoculars would show.

The image is a stack of four 2-minute exposures with the telescope guiding on the fast-moving comet. Comet Lovejoy is now at its closest point to Earth and moving fairly rapidly across the sky. So I guided on the comet, letting the stars trail slightly over the 8 minutes of exposure time.

The head of the comet glows bright green in photos, from glowing diatomic carbon, while the tail glows blue from other ionized gases streaming away from the head, or coma. The source of it all is a tiny icy nucleus completely hidden from view amid the glowing gases.

Comet Lovejoy was easy in binoculars, which showed a bare hint of the tail in dark skies. I could see the comet naked eye, but only by knowing just where to look. It appeared as a slightly fuzzy star, but unless you knew what you were looking at you wouldn’t know it was comet. This is a binocular comet for dark skies. But a very nice binocular comet.

– Alan, January 6, 2015 / © 2015 Alan Dyer / 

A Comet for Christmas

Comet Lovejoy (C/2104 Q2) on Dec 23, 2014

Comet Lovejoy has migrated from the southern sky to appear in our northern sky for the holiday season.

This was Comet Lovejoy, aka C/2014 Q2, as it appeared on Tuesday night, December 23. It was low in the south well below Orion in the constellation of Columba the dove. It was easy to see in binoculars as a 5th magnitude fuzzy star. My long exposure photo reveals its thin blue ion tail.

I could just see the comet naked eye, knowing exactly where to look. However, I’m at 32° North latitude, placing the comet now decently high in my New Mexico sky.

The comet was discovered by Australian amateur astronomer Terry Lovejoy last August when the comet was way down under in the southern sky. But it is now moving rapidly north and brightening, bringing northern observers a binocular comet for the holidays.

However, the Moon is now coming up and will interfere with viewing later in the week. However, in mid-January Comet Lovejoy will be very high in the sky as its moves through Taurus, with the Moon out of the way.

By then the comet may be brighter and a naked eye object from dark sites. But don’t expect it to be anything more than a fuzzy star. This comet never gets close to the Sun, so isn’t likely to grow a bright dust tail.

For more details see the SkyNews magazine web page.

– Alan, December 24, 2014 / © 2014 Alan Dyer