Category: Astronomy

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, Rocket Launches, and Fog

I went out to the Mormon Lake Overlook early last evening (12/08/2018) to photograph a couple of different events. First was the launch of the ULA Delta IV-Heavy NROL-71 mission from Vandenburg Air Force Base. After that, I planned on pointing the camera up towards Comet 46P/Wirtanen.

Comet 46P/Wirtanen.
Comet 46P/Wirtanen.

Only part of my plans worked out. The launch was scrubbed at T-7 seconds but I didn’t know about that until much later. I just kept shooting a series of 15-second exposures pointed towards the western horizon and hoping that I would capture it. No launch—and there was nothing to capture.

But, wait, not so fast! It turns out there was a shallow layer of fog in the Mormon Lake basin and the series of 15-second exposures over a period of about 10 minutes resulted in a nice time-lapse movie of the fog. Unfortunately, the camera was pointed at mostly sky with very little of the ground but I’m happy with the lucky result.

Time lapse showing undulations on the top of the fog layer.
Next, I shot a series of 60-second exposures of the comet. Although the skies were cloudless, there was a lot of moisture in the air. See the discussion above about fog! The presence of this moisture and very thin fog above resulted in very colorful stars. A nice effect.

Light pollution in the night sky.
Light pollution in the night sky.

For the third act, I pointed the camera back down and over the lake basin towards Flagstaff. The fog was dissipating at this time but still shows up well. What also shows up is the large amount of light pollution in Flagstaff. Flagstaff is the worlds First International Dark Sky City but it takes a lot of work to keep the skies dark. I fear we may be losing the battle.

Bright Objects in the Morning Sky — December 2018

The other morning promised an interesting alignment of the planets Venus and Mercury, the waning crescent Moon (3.4% illuminated), and the bright star Spica (Alpha Vir, the brightest star in the constellation Virgo) in the morning sky. All that was required was clear skies.

Morning twilight with Mercury, Venus, Spica, and the Moon (0629 MST 05 December 2018).
Morning twilight with Mercury, Venus, Spica, and the Moon (0629 MST 05 December 2018).

Various weather models showed essentially the same forecast. There would be a band of high clouds to our northwest and another band to our southeast. Overhead it would be clear.

And the forecasts turned out correct. Below is a satellite image taken at ~1330 UTC (0630 MST) showing a nice clear gap in the clouds.

IR satellite image at 1332 UTC (0632 MST) showing the gap in the clouds across northern Arizona.
IR satellite image at 1332 UTC (0632 MST) showing the gap in the clouds across northern Arizona.
Model forecast for cloud cover. White/gray is cloud; black is clear.
Model forecast for cloud cover. White/gray is cloud; black is clear.

I drove to the overlook on Mars Hill, home of Lowell Observatory, in Flagstaff. It has very good views towards the east and is a location I have used many times over the years for astrophotography.

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!

Comet C/2018 V1 (Machholz-Fujikawa-Iwamoto) in the Morning Sky

Venus and Spica in the morning twilight.
Venus and Spica in the morning twilight.

There’s a new comet in the morning sky. The comet was discovered in early November by three amateur astronomers—one in Arizona and two in Japan. Nowadays, most comets and asteroids are discovered by robotic Near-Earth-Object (NEO) search programs. The discovery of a comet by amateur astronomers is becoming a rare event.

So, with that bit of information, I set out to capture some images of the comet. As an 8th magnitude object it would not be easy using a short telephoto (i.e., 85mm focal length). My first attempt was marred by clouds but after viewing the images later I was finally able to find the small and not very bright comet.

A few days later I tried again. And, once again, high clouds moved across the sky. Finally, just before twilight, the clouds moved out of the way and I was able to get about 25 minutes of images.

 

Because the comet is so dim, individual images are not very revealing. In this case, better results are obtained by creating a short animation over the 25 minutes showing the motion of the comet relative to the stars.

As the eastern sky brightened the planet Venus and nearby star Spica stood out (image at top of post). A very nice end to a morning of shooting photographs in the cold.