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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.

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