Saturday, September 3, 2016

Meeting Night!

Last night was the first Friday of September, so was a general meeting night of the Tucson Amateur Astronomy Association. It has been a few months since I've posted about one, and for this one, both the beginner's and main lecture interested me, so brought the camera along to document. A few notes about that - I used the Canon 6D for the first time. In the nearly dark lecture hall, I was still able to get decent pictures of the speakers with a 15th second exposure, thanks to ISO 6400! However, since I wasn't sitting in the center aisle, the pictures on the screen were highly "keystoned" which was mostly squared back up with Photoshop... With everything going on in our lives, I don't make all the meetings, but they certainly are worthwhile for anyone interested in astronomy, since we draw on a wide variety of speakers and qualified members for some really interesting talks.

Ben Baily, shown at left, is our current president, serves as emcee, running the meeting and introducing business and speakers. As I indicated, we have some pretty advanced members, and last night had a few local celebrities join us. At right is David Levy, a well-known comet hunter with 22 comets to his or shared credits. He is also a noted author of astronomical-related works with 34 books, and founder of Jarnac Observatory! Behind him is Tim Hunter, a now-retired radiologist who co-founded the International Dark-Sky Association in 1987 whose mission is fighting light pollution, founder of Grasslands Observatory, and the author of a weekly astronomy column in the local paper.

For decades now, we've hosted a "Beginner's Lecture" an hour in front of the main lecture - really just a reason to hold a second talk! The club tries to schedule something that will appeal to those just getting into the hobby. Some of our main lectures given by scientists go way over the heads of many members, thus the idea for an introductory talk was introduced...

Tonight's warm-up talk was by member Mike Magras, who arranged a tour of the Torrance, CA plant of Celestron - one of the foremost telescope manufacturers for the amateur telescope market. Mike had some minor work done on his tube assembly, which resulted in the tour. Celestron was acquired by Synta Technoloty Corporation in 2005, most of the manufacturing capacity of all smaller optics was moved to Asia, with the exception of the 11" and 14" Schmidt-Cassegrains and the EdgeHD production line of the same size.

Celestron has been around a long time - nearly 50 years! Mike talked briefly about Tom Johnson, Celestron's founder when he introduced the compact optical design of the Schmidt-Cass. Actually, let me correct that - he didn't introduce the design, but rather, formulated an inexpensive way to make the complicated curve of the corrector optics. While the 4th-order curve can be polished into a thin piece of glass, testing and fabrication of the plate is involved and not for the faint-hearted! Tom developed the method shown at left - polish a "mandrel" of the inverse curve, and use suction to pull a thin plate into contact with it. The back is then polished flat and when the vacuum is released - presto, a corrector with the correct shape! While Bernard Schmidt himself used a vacuum technique to make the first correctors of the telescope that bears his name, it was Johnson's technique that allowed industrial production-line quantities of them...

In Celestron's current facility, most of the tube assembly is still made in Taiwan as shown at right - only the correctors for the above sizes are made in California, and the spherical secondary mirrors are supplied polished but uncoated - for reasons to be revealed shortly.

Part of the "secret" of the success of the larger sizes is Sandra - shown at left. She seems to be the magician utilizing the black arts in finishing out the optics. Assembling the correctors and primaries for the first time, she uses an artificial star for an initial alignment and has the skills to recognize errors that can be corrected by slight figuring of the spherical secondary mirror (why it was provided un-coated). Shown at her polishing stand, she has a hot plate for warming the pitch, a spindle in the white tub in the background, and uses a paper origami technique for making raised or lower areas on the lap to remove glass preferentially (inset).

When finished to her tolerance, the secondary is coated and installed in the final tube assembly where it undergoes one of the final tests, shown at right. In this setup, an artificial star enters the rear of the telescope through a beam-splitter, goes through the scope to a flat where it is returned to an eyepiece for a high-power view of the "star". Note that the 2mm focal length eyepiece, combined with the 4,000mm 14" telescope results in a magnification of 2,000X! And since it goes through the telescope twice (referred to as "double pass") it again doubles any potential errors, as if 4,000X were used...

After Mike's talk he answered a few questions - unfortunately for a group like this, there were some hard questions that couldn't be answered, but did what he could. We then had about a 20 minute break to stretch the legs and socialize a bit with friends before the main lecture started.

The main talk was given by Anjani Polit (at left, shown in inset), who oversees the science planning and scheduling for the HiRISE experiment of Mars Reconnaissance Orbiter, now in its tenth year of operation at Mars. The acronym HiRISE stands for High Resolution Imaging Science Experiment, and is effectively a 20" diameter spy telescope in low orbit around Mars. An incredible experiment, it can resolve details less than a foot diameter as it whirls in orbit 200miles above the surface.

As the image at right illustrates, it has assisted in surveying 7 landing sites and taken hundreds of thousands of images. While HiRISE has amazing resolution capabilities, the field is so small, only less than 3% of Mar's surface has been imaged with the highest resolution. With such resolution, it is almost as good as a lander at investigating virtually any spot on the surface and surveying it over a long period of time to look for changes.

Case in point for these temporal changes were shown by images that I've made into gif images here. At left are shown "Recurrent Slope Lineae" (RSLs) that occur as certain seasons that they think are briny deposits being carried down slope as underwater ices melt or sublimate.

Similarly, at right is shown a pair of images showing motion of a barchan sand dune over the course of a 3 year period. Look closely at the arrowed sections to see the obvious motion. With the high resolution of HiRISE, you can estimate that the entire dune is moving on the order of a foot every year given the scale at upper left... For dunes to maintain the shape and motion seen here, the wind in the thin atmosphere must maintain a nearly constant direction.

Other changes that have serendipitously been made with HiRISE are landslides along canyons or crater walls. Obviously you cannot plan to see these but have been spotted accidently, as shown at left. Other temporary phenomena like dust devils have also been spotted. At right are recent meteoroid impacts that are more obvious as they might be as they've broken into icy layers below ground level. They are demonstrated to be water or carbon dioxide ice as they melt or sublimate with the passage of time.

There are a wide assortment of "what the heck is that" moments seen in HiRISE data. At left is one from the polar regions that Anjani said scientists thought were from gaseous jets coming out of the ground affecting the frosts at ground level. And while you've already seen the barchan dunes above, seeing them in false color is another thing. She said (as I recall) that the observed wavelengths are blue/green, red and near-infrared, so the colors can be stretched and recombined into something that might not resemble how they would look to the eye. As a result, blue sand dunes!

I think one of the favorite images was taken early in the mission. They now have rules about spacecraft maneuvers to minimize the impact on other science experiments. As a result they only tilt a few degrees off-nadir, in other words, the spacecraft is almost always within a few degrees of looking straight down. Yet here comes this spectacular image of the moon Phobos, one of the most detailed I've ever seen, but to take it they certainly had to break the pointing rules, as Phobos is always at least 90 degrees off-nadir! Still, images like this, or of watching the Curiosity mission hanging below its parachute, and a few others as well brought gasps from the crowd.

She closed with a couple points of interest - there is a program called HIWish that is effectively a plea for the public to suggest places to observe. Since in 10 years they've only covered less than 3% of the area, they will never get full coverage, so they are looking for assistance in where to look. Click the link above for more information.

And finally, a video that compressed much of the wonder of her presentation into a perfect 2 minute performance (spectacular music!).  Click, turn up sound and go to full-screen HD and enjoy!

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