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View from the high ground

2020 June 4
by Russ

December 27, 2020

This recent imagery from NOAA’s GOES-East satellite shows sunset spreading across the United States from east to west leaving a trail of sparkling lights in its wake. We can also see a major winter storm barreling across the upper midwest into the northeastern U.S. and a new storm system entering the northwest U.S. from the Pacific Ocean.  Meanwhile, a large band of moisture-laden air streams into the U.S. from the Pacific and across the southern Rocky Mountains. Quite a busy but beautiful scene from the GOES-East satellite parked in its geostationary observing post 22,000 miles (36,000 km) overhead. GOES-East images are updated every five minutes. You can find the most current GOES-East imagery here.   Track GOES-East (aka GOES-16) here.

A Two Comet Night as a Lesson in Air Temperature and Humidity

2021 January 8

Three nights ago on January 5th, I caught two comets in one imaging session. The first, Comet 156P/Russell-LINEAR, was in the constellation Triangulum. The second, Comet 398P/Boattini, was in the constellation Orion.

Comet 156P/Russell-LINEAR

Comet 156P/Russell-LINEAR on January 5, 2021, 02:54-03:26 UT. At the time of this 30-minute animated sequence, the comet was 78 million miles away from Earth and heading just beyond the orbit of Jupiter where it will turn around to make another inbound pass through the inner solar system. With an orbital period of 6.4 years, Comet 156P/Russell-LINEAR should be back this way in 2026. In this image north is up and east is left. The field of view is 16’x12.’ [1]

Both comets were in the sweet zone for my telescope and camera combination. I estimated Comet Russell-LINEAR at magnitude 12.3 and Comet Boattini at magnitude 12.8. These magnitudes are 300 times fainter than the faintest celestial object that can be seen by a pair of very good eyes from a very dark location.

On the images posted here Comet Boattini is noticeably fainter than Comet Russell-LINEAR. Both were captured using similar exposure times and gain settings. Under these circumstances, they should appear of similar brightness. At the time, however, I was imaging Comet Boattini in comfort from inside my warm house, and failed to notice that the outside air temperature and the dew point temperature were converging near 31° F. This was serious negligence.

I didn’t realize anything was amiss until I moved on from Comet Boattini to my next target, the Pinwheel Galaxy (M101) in Ursa Major. This large galaxy fills the whole field of view of my imaging set up, but no matter how I worked the camera controls, I just couldn’t get anything better than a pale noisy ghostlike pinwheel to show up on the monitor.

Comet 386P/Boattini

Comet 398P/Boattini on January 5, 2021 06:39-07:19 UT. At the time of this 38-minute animated sequence the comet was 38 million miles away from Earth and heading outbound to somewhere between the orbits of Mars and Jupiter where it will turn around and head back toward the inner solar system. With an orbital period of 5.5 years, Comet 398P/Boattini should be back in our neighborhood in 2025. In this image north is up and east is left. The field of view is 17’x13’. [2]

Thinking that clouds had rolled in, I went outside to check. No, the sky was still beautifully clear. But upon reaching the telescope rig in the back yard the situation became apparent. The entire rig was covered in thick crystalline icy frost. Even the foam dew shield over the front of the telescope was covered with the stuff.

After removing the dew shield the source of the problem became even more painfully obvious. The corrector plate, the large flat glass lens that covers the front end of my Schmidt-Cassegrain telescope, was completely frosted over like a heavily frosted car windshield on a cold winter morning.

Needless to say, this ended the session. But, although I was tempted, I didn’t take an ice scraper to the corrector plate.

Temp-Dew Point Graph

This graph shows air temperature and dew point temperature from my back yard weather station on January 4-5, 2021. The area inside the red circle encompasses the time from midnight on the night of the 4th through approximately 01:30 a.m. on the morning of the 5th. This was when I was observing Comet 398P/Boattini. During this time the air temperature dropped below freezing, hovering around 31° F and the dew point temperature hung around 29° F. This temperature differential put the relative humidity in the 85%-89% range, a fraught range for astronomical imaging. With the air temperature and dew point temperature within two degrees of each other, moisture condenses out of the air to form heavy dew on all exposed surfaces, especially telescopes and their optical components. But in this case the situation was made worse by the subfreezing temperatures causing the liquid condensate to freeze as frost. This was the death knell for what started out to be a promising observing-imaging session.

I didn’t realize it at the time, but the frosting event had already started while I was imaging Comet Boattini. This explains why Comet Boattini is fainter than Russell-LINEAR in these images despite both being at nearly the same visual magnitude.

Nevertheless, the dew shield did its job. It delayed the inevitable onset of frozen dew collecting on the optics, but it obviously was overcome by the onslaught of humidity and below-freezing temperatures and succumbed.

Having once again learned a lesson about humidity, temperature, and telescope optics I now have a telescope dew heater on order and am anxiously awaiting its arrival! There are a few months of winter left. I don’t want to get frosted again.

Notes:

[1] This animated sequence was captured with a Celestron C8 telescope (203mm f/10) operating at f/5 with a ZWO ASI224MC camera. Each of the eleven images in the sequence is made up of a stack 11-13 sub-images, or frames, each exposed for 15 seconds.

[2] This  animated sequence was captured with the same equipment described in note 1. The sequence is made up of nine images, each of which consists of a stack of 11-13 frames, each exposed for 15 seconds.

Goodbye to Comet C/2020 M3 (ATLAS)

2020 December 30
by Russ

This animated GIF of Comet C/2020 M3 (ATLAS) consists of a sequence of six images aligned and overlaid one on top of the other. Each image is made up of a stack of eleven 10-second subimages. The 40-minute sequence was taken on December 27, 2020, between 02:49-03:31 UT with an 8” Celestron SCT (203mm f/10) operating at f/5 and a ZWO ASI224MC CMOS camera. The field of view is 17×12 arcminutes (0.28×0.20 degrees). North is up. East is left. You can see a full-size version of this animation here.

Although I had just observed and imaged Comet C/2020 M3 (ATLAS) seven days earlier, I was drawn back to it again. At first I thought it was because the moon was high and bright in the sky washing out faint galaxies and nebulae and making them unsuitable targets for the evening’s observing session. I also thought it was because the wind was really gusting, buffeting the telescope and making long camera exposures impossible. In retrospect, I realize it was because I was fascinated by watching the live images build on my screen showing this small fuzzy visitor in real time as it silently moved against the background of stars in the constellation Auriga back to its realm in outer solar system.

Comet C/2020 M3 (ATLAS) won’t be back this way for 139 years.  Its elongated elliptical orbit takes it out to 27 astronomical units from the Sun, or just inside the orbit of the planet Neptune, which orbits at 30 astronomical units (2.8 billion miles or 4.5 billion km).  At the time this animation sequence was captured, the comet was 50 million miles (81 million km) from Earth.

This animation shows Comet C/2020 M3 (ATLAS) at magnitude 13.0 (measured in the green channel), considerably dimmer than the magnitude 11.8 I measured seven days earlier.  As Comet ATLAS continues to recede from us on its run back to the deep reaches of the solar system it will continue to fade.  Soon, it will only be visible to the largest telescopes as a faint dot.

Report: Mars 2020

2020 December 27
by Russ

Unlike deep sky astrophotographers, we planetary imagers don’t need clear dark skies.  We need clear steady skies.  Steady seeing is good seeing. And good seeing is essential to capturing a crisp detailed image of a planet. In the case of the planet Mars, however, we need more than good seeing.

Because Mars is a relatively small telescopic target, it also needs to be at a place in its orbit where it is closest to Earth. When Mars is closest to Earth, it appears larger. A larger-appearing Mars allows planetary imagers to capture more detail in their images of the Martian surface and atmosphere.

Raw Video
Processed Image
Mars on October 10, 2020, four days after closest approach, and three days before opposition. The image on the left is a snippet of the raw video that produced the processed image on the right. Imagery was captured with a Celestron C8 Telescope (203 mm f/10), 3X Barlow lens, and a ZWO ASI224MC camera.

Mars was especially well placed for imaging in October. Mars was at its closest approach to Earth on October 6th, and reached opposition on October 13th.  At this opposition, Mars grew to an angular size of 22.6 arc-seconds.

Mars reached its maximum apparent size of 22.6 arcseconds for this opposition cycle on October 6th. This illustration shows how the Martian disc changes in size in the months before and after opposition and how that change in apparent size affects the amount of detail that can be seen from Earth and captured in telescopic imagery. Image Credit: Jeffrey Beish/ALPO-Astronomy.org

Knowing that nights of good seeing are rare at our home in Oklahoma, we set out for Rusty’s RV Ranch in southwest New Mexico in search of steady skies for imaging Mars during its 2020 close approach. Rusty’s prides itself on its clear dark skies and caters to amateur astronomers.

Unfortunately, while the skies at Rusty’s were clear and dark (ideal for deep sky astrophotographers, of which there were many present), for the week we were there, there was considerable movement in the atmosphere at both lower and upper levels.  This movement in the overhead ocean of air caused unsteadiness in the nighttime seeing.

At the high magnifications used for planetary imaging, this atmospheric turbulence caused the planet’s disc to bubble and boil in and out of focus.  And, to compound matters, southwestern New Mexico was covered at the time by a lingering persistent smoky haze from wildfires throughout the western U.S.  The smoky haze affected the transparency of the atmosphere and made it difficult for my one-shot color camera to draw out color from the small Martian disc, especially blue.  The lack of blue light making it through the haze is what I think caused Mars to have the off-yellow color shown in the raw video snippet above. It also means that my images show only Martian surface features and almost none of the atmospheric features (bluish haze, wispy clouds) captured by other planetary imagers.  All-in-all, while the planetary alignment was perfect for acquiring good images, the atmospheric conditions were not.

Nevertheless, while the seeing conditions throughout the week varied from extremely poor to poor-average, there were occasional short periods when the seeing improved enough to obtain the images shown here.  But, don’t get the idea that these images were just snapped at the telescope as one-time shots. It’s a little more complicated than that.

My observing and imaging setup at Rusty’s RV Ranch near Rodeo, New Mexico. The tiny red dot at the back of the telescope is the ZWO ASI224MC planetary imaging camera.

If you look real close at the picture of my imaging setup, you will see a little red object at the back end of the telescope. That little red dot is a sensitive video camera especially designed for planetary imaging.  The camera sends a high speed video stream of up to 100 frames per second to the laptop computer. Each frame in the video stream is a complete single image.

The idea is to capture a two or three minute video sequence consisting of several thousands of frames knowing that despite the constant wavy atmospheric distortions, with luck, some of the individual frames will be in better focus than others. Later when the video sequence is run through a specialized program, those higher quality frames are culled out, aligned, and stacked together into a single image. That single image is then manually processed using other specialized programs that apply sharpening magic and allow for adjusting color balance, removing noise, rotating, cropping, and other refinements.

This “lucky imaging” process is designed to get the best image possible when shooting through the undulating ocean of air between us and the planets.  The two images of Mars shown here are stacked images of the 2000 best frames taken from video sequences of six thousand frames each.

My images from Mars 2020 opposition week are on the left. The image on the right was taken by the Hubble Space Telescope during the August 2003 opposition. The Hubble image is annotated to show some prominent features.  Comparing the two, it’s pretty obvious that this year, Mars’ south polar cap is much smaller than it was in 2003. My images also show the Hellas Basin, an ancient impact structure that formed when a comet or asteroid struck Mars. Hellas is approximately 1,100 miles (1,800 km) in diameter. Also, just barely visible in my images is Schiaparelli Crater, another impact structure. Schiaparelli is approximately 277 miles (461 km) in diameter.  Lucky Hubble. It’s high above the atmosphere and always has good seeing! Image Credit: NASA and the Hubble Heritage Team (STScI/AURA).

In October when I captured these images, Mars was only 35 million miles away. As I write this in late December 2020, Mars is 79 million miles distant and presents a much smaller target. Some planetary imagers with larger telescopes at locations with more favorable seeing conditions continue to tease detail from the Martian disc, but this Mars apparition is over for me. I’m looking forward, however, to the next opposition, which will occur on December 8, 2022.  At that time Mars will once again be close, only 38 million miles distant, and back within the capabilities of my humble equipment.

A Christmas Comet

2020 December 25
by Russ

This Christmas season has a visitor to the inner solar system well placed for viewing in the pre-midnight sky. The visitor is Comet C/2020 M3 (ATLAS).

As of this writing, Comet ATLAS is in the constellation Auriga near the bright star Capella.  I happened to catch it last Saturday night.

Comet C/2020 M3 ATLAS on December 20, 2020.  This sequence of images shows Comet C/2020 M3 (ATLAS)  as it crawled through the constellation Auriga on December 20, 2020. This animation was cropped from an animation showing a larger area of sky. The size of this field of view is approximately 9.8′ x 6.6′, or 0.16° x 0.11°. North is up. East is to the left. You can see the full image here.

The image to the left is an animated gif covering a 47 minute period. Although the comet appears to be dashing across the sky, during that time, it moved just 3 arcminutes, or a mere 0.05 degrees.

During this session I estimated the comet’s magnitude as 11.8, although other observers were consistently estimating it as bright as magnitude 9.9. Unfortunately, even at magnitude 9.9 the comet is too faint to be seen without a telescope. Magnitude 6 is about the best the bare eyeball can do, and that’s from a very dark location with dark-adapted eyes.

Each of the seven images that went into this animated gif is made up of a stack of 10 to20 15-second subimages.  Images were live-stacked at the telescope with SharpCap and cropped and processed into an animated gif in GIMP.

Image Details:
Object: Comet C/2020 M3 (ATLAS)
Date/Time:  20 December 2020 06:34:01-07:13:34 UT
Telescope: Celestron C8 (203mm f/10) reduced to f/5
Camera: ZWO ASI224MC