Another look at Comet 46P/Wirtanen

Comet 46P/Wirtanen has already made its closest approach to both Earth and Sun and is now moving away. Yet it remains high in the sky making it an easy night-sky object if you are in a very dark location. It then appears as a full moon-sized smudge in the sky.

Comet 46P/Wirtanen. (Nikon D750; 200mm; f/4; ISO 1600; 120 seconds)
Comet 46P/Wirtanen. (Nikon D750; 200mm; f/4; ISO 1600; 120 seconds)

The full moon is now waning and rising later so that there are a few hours in which to observe the comet without the interference of moon light. We had one night without moon interference and without clouds so I took advantage.

Instead of taking multiple images and stacking I shot single images of 1, 2, and 3-minute exposure. Should have been easy. But there was a gusty wind blowing so that the camera and tripod was sometimes jostled resulting in streaky stars. And I had trouble focusing the telephoto lens I wanted to use (Nikon 70-300mm). Frustrated and cold, I grabbed my legacy zoom lens (Nikon 80-200mm AIS Manual Focus). This one is easy to focus on stars. Just rotate the focus ring all the way until it stops.

That’s the thing about some legacy manual focus lenses. They can be easier to focus than modern auto focus lenses in the dark so I keep several very old lenses around for that reason.

 

Meteors and Comets

The past few nights have been interesting. On the evening of December 13–14 was the peak of the Geminid meteor shower. This year the expected peak was around 100–120 meteors per hour and various meteor counts appear to confirm that number.

At the same time, Comet 46P/Wirtanen has been getting a lot of attention. On December 16 it made its closest approach to Earth—only 11.5 million km away. That’s about 30 lunar distances for reference.

From SpaceWeather.com: “Although the comet is very close to Earth, it is not very bright. 46P/Wirtanen is a relatively small comet and, thus, barely visible to the unaided eye despite its proximity. It is nevertheless an easy target for digital cameras. Even a short exposure reveals the comet’s spherical form and emerald green hue.”

During the late evening of December 13, I traveled to Wupatki National Monument because of its dark skies. I shot a sequence of photos—each of 30 seconds duration—of the night sky hoping to catch a few meteors. One bright meteor blazed across the sky and I was able to catch part of it before it moved out of the frame of the camera. At the same time, the crescent Moon was setting in the west and gently illuminating Wukoki Pueblo. At the very top center of the photograph is Comet 46P/Wirtanen.

Geminid meteor, Comet 46P/Wirtanen and Wukoki Pueblo.
Geminid meteor, Comet 46P/Wirtanen and Wukoki Pueblo.

After about 1/2 hour of shooting meteors, I shot longer exposures of the comet. On this night, the comet formed a triangle with the Pleiades and Hyades star clusters. The image shown here is from ten 60-second images stacked using Deep Sky Stacker (DSS) and post-processed using  rnc-color-stretch.

Comet 46P/Wirtanen with the Pleiades and Hyades star clusters.
Comet 46P/Wirtanen with the Pleiades and Hyades star clusters.

A few nights later, the comet had moved so that it was between the Pleiades and Hyades clusters. Again, I shot a sequence of 60-second exposures totaling about one hour in duration—this time from the Mormon Lake overlook. The motion of the comet is quite apparent in this sequence of images. The first image shows the motion of the comet against the stars; the second is a time-lapse movie of the same sequence.

The motion of Comet 46P/Wirtanen is seen as a short streak in this one-hour composite image.
The motion of Comet 46P/Wirtanen is seen as a short streak in this one-hour composite image.

Time lapse movie showing the motion of Comet 46P/Wirtanen during a period of one hour.

Comet 46P/Wirtanen is now moving farther from Earth and will slowly dim in brightness but it will remain visible through binoculors, telescopes, and with digital cameras for many weeks or more. There is still plenty of time to see the comet if you haven’t already.

Comet 46P/Wirtanen Approaches

The much-anticipated Comet 46P/Wirtanen is nearing its closest approach (approximately 30 lunar distances) to Earth. From the SpaceWeather.com site (cited 11/28/2018):

Small but hyperactive Comet 46P/Wirtanen is approaching Earth and could soon become visible to the naked eye. On Dec. 16th, the kilometer-wide ball of dirty ice will be less than 11.5 million km away–making it one of the 10 closest-approaching comets of the Space Age.

Earlier this week I made my first attempt at photographing the comet. I had patiently waited until the Moon was several days past full so that I could capture images of the comet without the interference of moonlight. I wasn’t successful because the moon was already rising by the time I was completely set up. Even with the bright sky in the presence of an 85% illuminated moon, I was able to get acceptable images.

Not only was this my first effort to photograph the comet, it was my first effort to even find it in the sky. Having a pair of binoculars helps.

I used a Nikon 85mm f/1.8 lens because it has a moderate field of view (24°x16°) and is a “bright” lens. It can [usually] successfully autofocus at night using bright stars, planets, or best, the moon. And, as I mentioned above, the moon was already above the horizon.

Comet 46P/Wirtanen (85mm, f/2.8, ISO 400, 15x60s)
Comet 46P/Wirtanen (85mm, f/2.8, ISO 400, 15x60s)

Later, I switched the lens and used my ancient manual focus Nikon 80–200mm zoom lens. This lens is almost 40 years old—and from the images it appears that it needs some servicing. Many of the stars have a “bulge” in the upper left. Maybe I’ll send it to Nikon servicing—if they still work on this old lens.

Comet 46P/Wirtanen (200mm, f/4.0, ISO 800, 6x60s)
Comet 46P/Wirtanen (200mm, f/4.0, ISO 800, 6x60s)

We are now entering an extended period of unsettled weather across the southwest U.S. and there may not be another chance to capture images of the comet for some time. I hope the weather is clear on the night of December 15 when the comet passes very close to the constellation Pleiades. That should make for an interesting sight!