Alagasta Victory Snatched from the Jaws of Defeat

Updated: 2002 October 28

This is the tale of the occultation of 8.9-mag. SAO 97305 by the 
asteroid 738 Alagasta that occurred Sunday morning, October 27;
the predicted central duration was 5 seconds.  Steve Preston's 
updated path for the event crossed the USA from southern California 
(over Salton Sea) to the Virginia part of the Delmarva Peninsula.

     There was joy and sorrow in Ladysmith, Virginia last night.
With persistence and luck, I videorecorded a 2.5-second occultation
at my location beside US 1 2 miles north of the main Ladysmith
intersection about 65 miles south of Washington, DC at
long. 77 deg. 31.030' W., lat. 38 deg. 02.870' N., h 220 feet (GPS).
The disappearance was at 8:29:37.5 UT and reappearance at
8:29:40.0 UT, to be refined later after I make a time-inserted copy
of the tape.  Unfortunately, Jeff Guerber and Bob Stewart, at
locations 2 and 4 miles south of me, respectively, were clouded out
a few minutes before the occultation, and so far, others that I have
heard from were also clouded out, from California to Virginia.  I
hope that there might still be an unreported positive observation to
determine something about the size and shape of 738 Alagasta, but
there was widespread cloudiness both according to reports and the IR
weather satellite images.  My location was 2 km north of Preston's
updated northern limit, at "34N" km, so there was apparently a small
north shift from his predictions; since my duration was less than
half the expected central duration (5.2 seconds), the actual
northern limit was probably only 4 or 5 km farther north.

     I describe my efforts below to possibly help others for future
occultations such as next weekend's much better Nephele event.
Basically, you need to be flexible and work efficiently, keeping
your wits to overcome obstacles.

FINDING AN OBSERVING SITE:  As mentioned in previous messages,
we had a plan to cover the Alagasta path, and we had high hopes as
the skies cleared across the Washington area and the infrared
satellite loop gave some hope that the clouds then over the path
might dissipate.  But our plans went out the window as we drove
under thick broken clouds about halfway between Washington and the
predicted northern limit, which was 1 km north of the Ladysmith exit
from Interstate 95.  Knowing that Bob Stewart had already decided to
try the event at Ladysmith, fearing thicker clouds farther south,
and arriving in the area well before the event, I set up a telescope
with a Watec camera 11 km farther south, in the path at "20N" south
of Carmel Church, VA at a deserted construction site.  Through
breaks in the clouds, I focused the video on the Moon and aligned
the finder.  But without being able to dwell on star fields, there
was no hope to accurately point the telescope.  1.5 hours before the
occultation, I went 8 km farther south to Doswell, to meet another
observer coming south from the DC area; he didn't bring his cell
phone.  He set up there, I measured his position with the GPS unit I
borrowed from Wayne Warren, and I returned to my telescope near
Carmel Church.  I watched the sky for several minutes; it was worse
than before, almost completely overcast.  Remembering the larger
breaks in the clouds farther north, and knowing that in general it
was better to the north, I decided to drive to Thornburg, north of
Ladysmith to get a different chord from the others, to set up
another telescope there; now there was no chance to run a remote
station, as I had hoped earlier, and it looked like there was little
chance to see anything; I felt sorry that I didn't instead try a
graze with a good profile promising many events in northern Maryland
that occurred about 20 minutes after the asteroid occultation (no
way to do both; the paths were 100 miles apart).  But Thornburg was
22 km north of my Carmel Church site and it took longer than I
thought to get there.  During the drive, there was a substantial
clear area around Ladysmith, but at Thornburg, it was cloudy again.
I headed back south, thinking that I could still get to my telescope
at Carmel Church and hope for a break in the clouds there.  But as I
approached the Ladysmith exit, I could see a lot of clouds in the
south again; going to Carmel Church would mean almost certainly
being clouded out, while near Ladysmith, there was a chance.  I got
off I-95 there, drove west to nearby US 1, and drove north on it,
both to get away from the other observers and to get closer to the
center of the clear area, even though this was a little outside the
predicted path.  I decided that a miss observation was better than
nothing, and there was probably about a 40% chance of a north shift
that would give an occultation there.  There were a lot of houses
along US1, and I didn't want to set up near a residence at 3:30 am
unannounced.  Finally I drove into a temporary gravel driveway to a
house under construction and stopped several feet east of US 1,
which had almost no traffic that time of night.

FINDING THE TARGET STAR:  There was less than half an hour to the
event and I had not had a chance to find the target star before.  I
quickly set up my 2nd C-8, only roughly aligning with Polaris - no
time to adjust the wedge or tripod leg to tweak the latitude angle.
Rather than an eyepiece, I slipped a PC-164C camera in the eyepiece
holder, also using an f/3.3 focal reducing lens to get a larger
field.  Going directly to video saves time, and I've become as
accustomed to that as visual observing with an eyepiece.  But the
telescope is old, not a GO TO scope.  The gibbous Moon 16 deg. away
didn't help, except that it was handy for focusing and finder
alignment.  By naked eye, I could see Castor, Pollux, and Alhena
(gamma Gem), but had to strain to see any of the other stars.  At
this point less than 15 min. to go, Jeff Guerber called on my cell
phone, wanting to know for how long to observe; I had not put a
recommendation of that in my message.  I was busy, but told him to
observe from 1 min. before to 1 min. after; in general with short
events like this, that's enough, to cover 10 times the central
duration that will include the space where nearly all known
asteroidal satellites are located.  After hanging up, I aimed the
telescope at Alhena, then slewed east in RA to see in the 60mm
finder scope lambda Gem, then 68, 74, and finally 81 Gem (in
retrospect, it probably would have been a little easier to move
directly south from Pollux to 81 Gem).  Finding 81 Gem in the video
field, I noticed about 8 min. left to the occultation.  I moved a
little north, not carefully measuring the amount, and turned off the
clock drive, knowing that 5 min. later, the target star should
appear some 10' north of where 81 was.  During those 5 minutes, I
got out my Timekube and turned on WWV, and connected a PA3
microphone with its 9-volt battery adaptor as input to the camcorder
that I was using to record the video.  Opening the flip viewer
turned on the sound, producing feedback, confirming that the PA3 was
working.  After 5.0 minutes, I plugged the telescope drive cord back
in, and confirmed the telescope was tracking, but the star was not
in the field, with only 3 minutes to go!  I figured that I must be
at the right R.A., and looked in the finder, seeing 85 & 81 Gem, and
the 6th-mag. star 1/3rd the way between them.  I could also see that
the crosshair intersection was too far south, and so I moved north,
watching the video, and finally a reasonably bright star appeared;
with the Moonlight, I couldn't see any of the few stars of almost
12th mag. in the vicinity of the target star.  I looked in the
finder; now it looked like the crosshairs intersection was in the
right place; since there were no other reasonably bright stars in
the area, I assumed I had the target star (SAO 97305) in view.  I
started the recording, and soon heard the 8:29 minute announcement;
realizing this was the critical minute, I would soon know if there
was a north shift or not.  Bingo, the star disappeared, I knew I had
found the right star!  Very soon after, it reappeared, and I tried
to record the WWV signals more clearly, but the Timekube only had 10
megahertz whose reception was poor; I had not taken the time to
string out the 23-foot Radio Shack antenna.  Instead, I got out my
Grundig digital radio and turned it on, already tuned to WWV at 5
megahertz, and received a clear signal.  I could see the clouds to
the south moving into Gemini, and wondered how the others had done.
Five minutes after the occultation, the clear area closed up and it
became overcast.

      Note that finding ZC 593, the 5.5-mag. target star for next
Saturday night's Nephele occultation, will be much easier; not only
is the star bright enough to see easily in finder scopes and
binoculars, but also it is between two familiar star clusters, the
Pleiades and the main Hyades "V".

      It was a relief to be able to use I-95 without fear of being
shot or caught in a police dragnet following the recent arrests.
For Alagasta, I felt vindication after the miss I had at the 161
Athor occultation in Texas 11 nights earlier; that path also shifted
a little north, but then I was near the predicted southern limit
rather than the northern limit.  Alagasta was the 6th asteroidal
occultation that I've observed this year, all video recorded.  I
believe that this is the shortest asteroidal occultation that I have
observed.

David Dunham, IOTA, 2002 Oct. 28, 5:40 UT

P.S.  Several other observers across the USA, including Joe Sedlak 
at Doswell, VA, reported that they were clouded out; as far as I 
know, nobody else observed the occultation.