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Spacewatch

domes

Above: The two domes of Spacewatch on Kitt Peak.


On January 9, 1999 Larry Robinson and Ron Abbott had dinner with Jim Scotti , one of the astronomers working at the Spacewatch project at Kitt Peak. During dinner Jim told us his interest in astronomy really began when he was about 10 years old living in Michigan. He was impressed by the Apollo moon landing and decided he would like to be either a geologist or an astronomer. Jim got a toy geology lab for Christmas and later a 60mm refractor and decided he liked astronomy more. He studied astronomy in college and is currently working on his PhD through Queens University in Belfast.


Jimís interest in minor planet research was stimulated by his friendship with Gene Shoemaker and others. He told a story about going down into Meteor Crater in Arizona with Gene Shoemaker. He was amazed that such a huge crater could be left by the impact of just a 30 meter asteroid.


After dinner Ron and Larry accompanied Jim to the Spacewatch telescope where he was getting started on his second night of six in a row using the 36" Newtonian equipped with a super-cooled CCD camera. The telescope is an F4.5 36" made originally in 1921. It was moved from the Arizona University campus for use by Spacewatch and later the drive was upgraded from the old pendulum drive to a servo motor drive. The old pendulum drive is still there and a unique engineering design. The way it worked is a heavy weight was lifted up and allowed to slowly pull a cable that drove the telescope. When it hit the bottom it was rewound and started over. The new drive is continuous.


The telescope must be moved by the observer to each new field being observed using the slewing controls. There are many possible obstructions like the platform and other objects which must be watched carefully to avoid a crash. Jim told us about a few of the incidents that have occurred.


The camera has side by side large CCD chips and is cooled by liquid nitrogen. Jim took a canister of liquid nitrogen up on the platform to top off the liquid in the cooling chamber. The camera is in continuous communications with a computer in the control room and reads out each row of pixels as they are exposed providing immediate images of a wide section of sky. This continuous download allows the camera to scan large sections of the sky.


The way a session works is Jim points the telescope at the part of the sky he wants to scan and then turns off the drive allowing the sky to pass across the chip while the CCD camera downloads the image continuously. Three passes are made of the same exact ribbon of sky.


On the first pass the telescope looks for all of the known stars in the area and registers them using the Guide Star Catalog. This will later be upgraded to use the USNO catalog. This first pass identifies all known stars and measures the seeing conditions and other important calibration information. It is also identifying any streaks which could be caused by fast moving Near Earth Asteroids. Most of these are not NEAís but rather spikes of bright stars, unresolved double stars, and those pesky galaxies. It is fascinating to sit there beside Jim Scotti and watch the sky pass before you one band at a time at mag 21. Many deep sky objects are seen as they slowly pass across the screen and Jim can take snapshots of these, process them and save them as the camera takes its pictures. The entire pass takes about thirty minutes. You can do the math on how much sky is covered at about a two degree wide second rolling by for thirty minutes on continuous drift but if is a large swath.


After the second pass Jim moves the telescope back to the beginning and starts the second pass. On the second pass the telescope is looking at the streaks and seeing if any of them moved. If not then they are eliminated as possible NEAís. The third pass is the real discovery pass. The computer is looking for faint objects that have moved an equal distance across the field during the three passes and offering these up for consideration by Jim as possible asteroids. By the end of this pass the computer had offered about 80 possible asteroids for consideration and about 45 were probable asteroids. All but about 6 of these 45 were new discoveries.


This completed the first session and took about two hours. Jim planned to do about five more such sessions and expected to identify about 400 new asteroids for the night. The objective is to find those that are Near Earth Approaching objects, and usually 3 to 5 are. Some of these observations may result in improved orbits for asteroids previously discovered and then be numbered and named once the orbit is known. There are just under 10,000 numbered asteroids. Jim thinks that the numbering has slowed waiting for a decision on designating Pluto as asteroid number 10,000.


In addition to finding new asteroids, Jim is also looking for new comets and recovering existing comets. During our visit he showed us the images of Comet 128P Shoemaker-Hart 1 that he had taken the night before. This comet had split into two pieces and both had tails. This is very similar to what happened to Shoemaker Levy 9, except on a smaller scale. He processed the images, did the astrometrics and emailed his report to the MPC while we were watching. Donít bother looking for this pair near the Leo Sextans border, because they were mag 20 and 22.


Jim says he has not gotten his name on a comet yet. His three partners all have so far. But he has named numerous asteroids including Asteroid 4255 Spacewatch and he has an asteroid named after him Asteroid 3494 Scotti. Jim also is credited with discovering the first Near Earth Asteroid 1991 BA, the closest NEA 1994XM1, and smallest 1993KA2. His most famous discovery was 1997XF11, the one that was initially reported to be a possible earth impactor. Jim said he got on TV over that one.


Jim said they will be turning on a new 1.8 meter telescope in the new Ash dome in May and it will be totally automated. The old 36" is being equipped with a new faster computer soon and then both scopes can be run by one person more than doubling productivity. The objective is to discover all NEAís within the next ten years. As Jim Scotti said it is impossible to really do anything about most of the natural disasters we face, like hurricanes, tornadoes, and earthquakes, but earth impacting asteroids and comets are predictable and there is a possibility we could do something to save lives and avoid disaster. It is great to know that Jim Scotti and Spacewatch are committed to their job.


As I sat with Jim Scotti and watched him work my mind began to wonder to how I could set up a scanning system like this at the Sunflower Observatory. Perhaps my upcoming visit with Roy Tucker would provide the answers...


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