Asteroid Occultation of Star

posted Aug 7, 2009, 2:23 PM by James Roe   [ updated Jun 19, 2010, 6:36 PM ]

An occultation of the star 32 Lyncis by asteroid (372) Palma was predicted by the folks at IOTA (International Occultation Timing Association) for the early morning (CST) of January 26, 2007. The predicted path from which the event could be observed passed (relatively) near to my home in Wentzville, Missouri.  Wayne Clark and I decided to try to observe the event.


Accompanied by or wives, Yvonne and Nancy respectively, we drove 110 miles north on US 61 to LaGrange, Missouri (about 30 miles north of Hannibal). Our original goal was Wakonda State Park which is just off the highway at the turn off to LaGrange, but it was closed. So we journeyed a little farther and pulled off at a rural intersection to see if we wanted to try it out - we didn’t as it was still ice and snow covered from the previous snow (they got a lot more up north than we did in St. Charles County). When we tried to back up, we couldn’t. Very slick!. After a good half hour of rocking, women and children pushing, pulling some vines off a nearby tree to put under the wheels (sure hope it wasn’t poison ivy) we finally got free. Did any of you know that astronomy has cardio-pulmonary benefits?

Heading on in to LaGrange we discovered that Terribles Casino had cleared their huge parking lot although the level of wattage on their parking lot lights probably could have melted the snow and ice without any atmospheric warming. (As we pushed and struggled and slipped trying to free our vehicles from winters icy grasp, we noticed a lot of traffic coming from the direction of LaGrange - at 1:00 am to 1:30 am - but those locals didn’t seem interested to stop and give city slickers (Freudian slip?) a helping hand/push. The sight of Terribles Casino cleared up the mystery: they were broke gamblers who were probably afraid we’d beg them for money that they didn’t have (anymore)).

We checked out the parking lot and decided that we could see our target star and, maybe, get a nice tan at the same time even if it was 22 deg. F. But like trolls who crave the darkness, we decided to explore just a little more and found a small public park where the street-side parking had been scraped (sorta) and there were only two streetlights, so we set up there.  Both of our GPS receivers put the location at 40 02.679 N, 91 30.124 W and 611 feet elevation.

The night patrolman soon spotted us but drove on by, so we figured he was benign. But he circled the block and came back after deciding he couldn’t believe his first observation. He rolled down his window (staying inside the nice warm patrol vehicle) and allowed as how he recognized those funny objects as telescopes (at least mine, but he wasn’t too sure about Wayne’s) but, even so, were we crazy to be in LaGrange, Missouri at 2:30 am in frigid weather? We said yes (seconded by Yvonne and Nancy - who also stayed inside the nice, warm(er) vehicles), and he went on his way.

We finished setting up the 8-inch SCTs (Meade LX-200 and Celestron whatever) and found our target star quickly (we had actually found it from my backyard in Wentzville with 7×50s before we set out). Of course, as there were two similar stars in the field of view and the field was upside-down, reversed and otherwise convoluted, we debated over whether up in the eyepiece was east or west.

With some 30 or so minutes to spare, I studied the candidate star and finally detected the asteroid just east (up) of the target. I guess I was surprised at how faint 10.5 mag appeared in the 8-inch, but then we were no ways dark adapted with the two street lights nearby.

Wayne had brought along a couple of portable WWV receivers and we set them up on a folding table (unfolded, of course) and placed our sound recorders nearby. Then we sat down to keep steady, if teary, eyes on the target as the time ticked away. At shortly after 9:45 “Coordinated Universal Time.” the star disappeared. Wow. We hollered out “one” to record the event on the recorders although Wayne beat me by a fraction of a second. When the star reappeared, Wayne hollered out “two” and I missed it. While waiting for these events to happen, one purses the lips to be absolutely ready, but I think mine froze, or at least stiffened in the cold.

Upon reviewing my recording I found good data (haven’t heard from Wayne, I suppose he is still sleeping as I write this - but one recording will get us through if need be). The time signal and “one” and “two” can be heard plainly.  Using a stop watch and repeating the measurements several times to get an average, I put the start of the event at 09:45:05.03 (UTC) and the end at 09:45:18.27 (UTC) so the event lasted just over 13 seconds at our location.  We will submit the timings to IOTA along with our latitude and longitude as determined and cross checked by our two GPS units. Hopefully other observers across the country got good data and these data will be combined to yield an estimate of the cross section of the asteroid and improved orbit parameters.

Usually, a plot is prepared showing all the chords of the profile and I will post it when it becomes available.

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