Comet C/2021 A1 (Leonard)—IV

January 3, 2022 / Add comment

It’s been awhile since the last post about the comet—but cloudy skies with lots of rain and snow have made observations difficult. Finally, we had a break in the weather on New Year’s Day and I was able to capture additional images.

The comet has dropped lower in the sky making it difficult to get good images because the comet is now located in the band of twilight glare. Only at the end of astronomical twilight is the sky dark enough but by this time the comet is very low on the horizon leaving only minutes to shoot until it sets.

Below are two images of the comet. The first is a set of images taken between 1832 and 1850 MST. The best 30 images were combined and averaged in Starry Sky Stacker then histogram stretched using rnc-color-stretch. Individual images were shot at 85mm, ƒ/4, ISO 100, and 15 seconds. The resulting image shows the tail extending nearly to the upper left corner.

Comet C/2021 A1 (Leonard) at 1832–1850 MST 01 January 2022.

Comet C/2021 A1 (Leonard) at 1901 MST 01 January 2022.

The second image is a single image taken at 1901 MST at 85mm, ƒ/1.8, ISO 500 and 30 seconds. This image shows how close the comet was to the horizon. The glow at the bottom of the image is the light dome from Phoenix about 200 km to the south.

The comet is moving away from us and lower in the sky. I’m not certain I will be able to get another chance to capture any images. For those in the southern hemisphere, the comet is better placed in the night sky for viewing and photography and there have been some amazing images captured. Spaceweather.com noted that “…Intense solar heat has given the comet one of the most beautiful tails astronomers have ever seen…”

Atmospheric River Over Arizona

December 24, 2021 / Add comment

We had a very wet period from late afternoon Thursday through early evening Friday (12/23-12/24) as an atmospheric river (AR) moved across the southwest and Arizona. From the Wikipedia site:

An atmospheric river (AR) is a narrow corridor or filament of concentrated moisture in the atmosphere. Other names for this phenomenon are tropical plume, tropical connection, moisture plume, water vapor surge, and cloud band.

GOES-17 water vapor channel showing the moisture plume.

An approaching trough of low pressure was able to tap into tropical moisture and move it across the southwest into Arizona overnight. Interestingly, the moisture plume aloft initially moved above a drier layer of air. Precipitation falling into this drier air experienced strong wet bulbing and evaporative cooling which lowered snow levels to ~6500 feet—putting Flagstaff into the snow. As the plume continued, these cooling effects diminished and the snow turned into rain. So we had about 4-6″ of snow followed by day-long rain. What a mess.

The Center for Western Weather and Water Extremes provides forecasts for ARs moving into the West. Below are some of the products valid at 5 A.M. Friday (12/24/2021) that clearly show the plume of moisture.

Integrated water vapor (iwv): Note how the moisture is depleted as it crosses the Mogollon Rim with very little moisture available across NE Arizona.

It’s great to get all this moisture although it would have been much better if had been either all rain or all snow. Mixed precipitation is always a mess.

Comet C/2021 A1 (Leonard)—III

December 21, 2021

Comet C/2021 A1 (Leonard) remains a visually interesting object in the evening twilight. It is only visible for short time each evening between the time it gets dark enough to see it and when it gets too low on the horizon and is obscured by dust or clouds.

Comet C/2021 A1 (Leonard) at 1833 MST 20 December 2021. Image has been inverted to help show the fine structore of the tail.

Comet C/2021 A1 (Leonard) at 1833 MST 20 December 2021.

The comet has undergone a rapid brightening in the past few days. From Spaceweather.com:

The outburst might signal a fragmentation event in the comet’s core. This would come as no surprise. The comet is heading for its closest approach to the sun (0.61 AU) on Jan. 3rd. Increasing heat may be liberating new jets of gas and dust from the comet’s core—or worse, blowing away huge chunks of ice and rock.

There have been numerous magnificent images posted to the Spaceweather.com website:

In the southwest we are heading into an extended period of cloudy skies with rain and snow so it is unknown when I will get another chance to shoot photographs of the comet.

Comet C/2021 A1 (Leonard)—II

December 19, 2021

Comet C/2021 A1 (Leonard) is currently visible in the southwest evening sky for a short period after sunset. Evening twilight makes it difficult to see the comet with the unaided eye. Even in binoculars it is a faint object. On the other hand, a short exposure on a camera will reveal the comet and its tail.

A nearly-full Moon illuminates the snow-covered San Francisco Peaks as the comet sets in the evening twilight.

Telephoto view of the comet and tail. (Stack of 13x15seconds, 300 mm, f/8, ISO 400.)

Finally, here is a time-lapse of the comet on 17 December 2021 from 18:16:48–18:21:08 MST. It moves quite a bit in just a few minutes.

Time lapse of the comet.

The comet will reach its highest elevation above the horizon this week and then begin to slowly drop towards the horizon again.

A Frosty Morning in Sedona

December 15, 2021

Last week we headed down to Sedona for a trail run. Because of a recent rain event followed by a very cold night there was frost on the ground and some of the vegetation. Especially wonderful was the spiky frost on many rocks and tree roots.

It was beautiful—and it didn’t last long.