It was Saturday, December
9, 1995. Being only a few of days past full moon, there were no
serious plans for observing. That was until Erik reminded me about
a premier occultation scheduled for early that evening. 11th magnitude
asteroid 85 IO was predicted to occult 8th magnitude star SAO111235
in Taurus at approximately 6:42 p.m. CST.
The path from which the occultation
was visible was published in the February 1995 and December 1995
issues of Sky & Telescope. This path was originally predicted
to be approximately 200 km wide, extending through southern Kansas.
As the time of the event drew near however, the path was redrawn
250 km farther north and posted on IOTA's web page (International
Occultation Timing Association). This meant that the occultation
should become visible about 80 miles south of Lincoln. Saturday
afternoon, we decided to venture south to observe this event.
With a Kansas map, we found
a potential observing site 10 miles south of Marysville, Kansas,
or 1.5 hours from Lincoln. If we hurried, we would have just enough
time to get there. We used MegaStar to print out several detailed
star maps to assist in locating the correct star and one chart
showing magnitudes of surrounding stars to allow us to estimate
magnitude drop. We planned to observe through my 20" Dobsonian
and Erik's 6" Newtonian. After loading up our equipment,
we stopped by Hyde Observatory and picked up a WWV radio that
could receive timing signals. We also brought along a portable
tape recorder. Soon we were on the road.
It was an extremely clear
afternoon as the sun set and stars began to appear. We closed
in on our observing location, but time was running short. We found
the site ok but there were trees all around and it was right next
to Hwy 77, so we headed east and found an access road leading
onto farmland. There were no houses around so we decided this
was it. The clock told us it was our only hope. It was after
6:20 p.m.
We began setting up in record
time. There was snow on the ground and it was mighty cold (lower
single digits). By about 6:35 we were set up and collimated. Now
we had to find the star. This really put our star-hopping skills
to the test, but within 3 minutes we found it and confirmed it
with the charts. The asteroid was not visible; it must have been
too close to the star. Then there was the inevitable problem of
warm optics. The stars were much larger than usual and would oscillate.
But it would have to do, so we turned on the radio and the tape
recorder and began observing. 6: 42 p.m. came and went, as did
6:43, 6:44, & 6:45. Then just before 6:46 p.m., Erik thought
he saw the star flicker, then we both saw the star began to dim
and remained that way for nearly 20 seconds. We wondered if we
actually saw the occultation or if it was an atmospheric phenomenon.
It was then that we realized
we were cold. I hadn't even put on my boots or my winter pants
yet! Climbing into the car, we turned on the radio and they reported
the temperature at a mere 3 degrees Fahrenheit. After warming
up with coffee, we continued observing. By now the scopes had
cooled and the stars were much more pinpoint in appearance. At
7:16, a dim "star" appeared to the lower left of SAO111235.
It was the asteroid! We observed it for nearly an hour and it
appeared to brighten as it moved away from the star. This left
no doubt that we had been watching the correct star. We only wished
we had been there early enough to see the asteroid before the
occultation, but all-in-all, it was a great experience. It was
incredible to comprehend an asteroid 150 km across occulting a
star much larger and farther away, leaving a narrow path cutting
across the midwest. It was coincidental that we drove nearly 150
km to see the event (136 to be exact)!
The following Monday, we submitted
our results. Both of us were surprised to find that we had co-observed
with approximately 30 other astronomers from Sweden, Newfoundland,
Ontario, Missouri, Kansas, Arizona and California. The Telescopes
used ranged from a 4" to a 30". One pair of 11 x 80
binoculars was also used. IOTA reported that "more chords
were observed for this event than any asteroid occultation event
since 1991". After interpreting the results, it turns out
the asteroids shadow path was really an additional 100 miles south
and the event just missed our site. However our results help to
define a northerly extent for a diameter measurement. Had we been
in the asteroids path, we would have seen the 8th magnitude star
completely blink out - for 18 seconds.
Martin Gaskell was quite interested
in our observation and attempted to help us explain what we might
have seen and why is was about 3 minutes late. Was it the unsteady
optics, or perhaps is there a secondary star to SAO111235? Could
it be that the asteroid IO 85 has a companion? What Erik and I
do know is that this event was fun to do, and we intend to observe
stellar occultation's in the future. The next time we won't be
so rushed and we will let our optics adjust to the temperature.
With email and World Wide Web sites, reports can be shared easily
and results known very quickly. It was a chance to participate
in some real science.
Timing occultation's are new
to both of us but we're looking forward to many more. We encourage
others to give it a try as well. If you would like more information,
look up http://www.anomalies.com You'll see our report
as well as others. Information about IOTA can be obtained from
Terri & Craig McManus, 2760 SW Jewell Ave., Topeka, KS 66611
(913) 232-3693. They also have an article in both the January
and February 1996 Sky & Telescope Magazine.