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| 33 years ago |
Circumstances
The path of totality for the solar eclipse of Feb. 26, 1979 covers the northwestern part of the United States and runs across Canada towards Greenland. "At 8:12am, the umbra first touches land on the Oregon coast. The shadow sweeps along a 170-mile-wide path blotting out the Sun for up to 2 ½ min in southern Washington and northern Oregon" [Brewer p.74].
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| Brewer p. 78 |
from Brewer p.78.
Corvallis, hometown of Oregon State University and the "Beavers" would be just inside the totality zone. So why not just stay there and watch it in comfort from the beautiful Willamette Valley? Consider John Steinbeck, who wrote in”Travels with Charly”: "It was Sunday and it was raining and it was Oregon".
A site was carefully selected near Madras in the rain shadow east of the Cascades range.
The OSU eclipse expedition was part of a larger effort organized by the IOTA (International Occultation Timing Association) and the USNO (United States Naval Observatory). Specifically eight teams participated, two from Oregon (Oregon State University Corvallis, Central Oregon Community College, Bend), others from Montana, North Dakota, Saskatchewan and Manitoba).
The common objective was not to see maximum duration from a place on the centerline.
Observations of scientific value, e.g. of the corona would have required the best equipment available. Instead, observing locations close to the southern shadow limit would be chosen. The goal was to determine the actual shadow boundary by observation. Further measurements would be the exact timing of 2nd and 3rd contact as well as Baily’s Beads.
Detailed observing program and scientific background
All previously published maps of totality zones had apparently been in error often up to several miles. The data referred to are the eclipse predictions from the American Ephemeris /Astronomical Almanac.
For the eclipse of February 1979 for the first time improvements were made:
* The actual lunar limb profile was accounted for.
* Lunar laser ranging data – incorporated into moon orbit.
* The difference of the center of gravity and the center of figure
of the moon was accounted for.
* The JPL Solar ephemeris was adjusted for meridian circle observations
and solar system spatial data gained from radar tracking of space probes
were taken imto account.
* Also the height of the observing location above sea level must be taken into account: for each 1000 ft. the shadow zone shifts 2000 ft. towards the south.
The coordinates for Madras, OR are: Latitude 44° 38' N, Longitude 121° 08' W, elevation 2280 feet. According to the American Ephemeris, Madras would have 36.7 seconds of totality.
As a result of the new calculations, the southern limit of totality was predicted to be 4 miles north of the graze line as published in the American Ephemeris. The accuracy of the new calculation was expected to give the lunar direction accurate to 0.2 arcsec. This translates to 0.5 miles on the ground. So in this vicinity a string of observers had to be arranged perpendicularly to the direction of the shadow’s motion, thus allowing comparison of theory and observation.
Further insights to gain from the observations would be:
* Refinement of certain astronomical parameters like
- Diameter of the Sun
- Motion of the lunar nodes due to tidal friction.
At the time scientific debates were held about the "shrinking sun" and the possible variability of the gravitational constant.
An observing position just inside the totality zone is not as bad as it might seem at the first moment, it even has some advantages:
* The chromosphere would be visible for about 30 sec instead of typically 3 sec from a location near the center line.
* Baily's beads last longer, are more numerous.
* Shadow bands might be more prominent.
Only 4 miles inside the totality zone the duration of totality would be already 40 seconds, 1 mile inside 20 seconds.
The OSU Solar Eclipse Expedition
The OSU team consisted of about 20 observers, mostly students and staff from OSU. It was lead and organized by Robert Dale Hall, an astrophysics graduate from Rice University and then in a doctorate program in history of science at OSU.
The largest instrument was an 8 inch Schmidt-Cassegrain - operated by the expedition leader.
In addition to the standard observing procedure for the IOTA, some members made specialized observations:
* Watch for shadow bands on the ground.
* Take a flash spectrum.
* Make a 16mm movie.
* Take a position on a mountain top to get a better view of the approaching shadow.
* Prof. Larry Schecter observed from a plane.
The observation teams were placed along a north-south running road (N. Adams Dr.) northeast of Madras with a spacing of 400m=1320 ft. The position just at the predicted shadow limit was labeled 1+0000. My station was 1+2640, i.e. at 2640 ft (800m) north inside the predicted totality zone.
/* 1+0000 probably referred to the interior limit of the graze zone, see
Espenak
"The graze zone is typically five to ten kilometers wide..." */
The Eclipse
Taking the route via Santiam Pass, we arrived late in the evening of Feb 25 at the Greene Brothers farm on the Agency Plains near Madras, not far from the planned observation location. At 10 p.m. the sky was still totally overcast - so we unrolled our sleeping bags in the big barn, hoping the best for the upcoming eclipse day. The morning of Feb. 26 dawned with nearly all the clouds gone. The sky was very clear, little wind and the temperature was above freezing - everybody was in a good mood. So all observers moved to their predetermined positions, spread along the road (N.Adams Dr.). Everything was ready for the big event to occur at 08:14 PST.
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| observing station 1+2640 on N. Adams Dr. |
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| panorama, shortly past totality |
At Station 1+2640 I was accompanied by Helen Lowry (OSU) and Abdul Rahman Pilus, a student from Malaysia.
Our equipment consisted of:
* Radio for WWV time signals from Ft.Collins, CO.
* Tape Recorder
* Small Telescope 30X, for projection
* Shadow band setup
(large white screen leaning upright against a chair large kitchen clock)
* SLR cameras
Observation of the Eclipse
At the time of first contact (07:10) the sun was 4.5 degrees above the horizon and
obscured by clouds. Shortly before 8:00 everything was set up and the progress of the eclipse was evident. The tape recording starts at 07:57 PST and lasts for 28 minutes.
[ecl1979_tape.mp3]
Totality lasted from 08:14:00 until 08:14:19, i.e. 19 seconds.
Due to the location near the graze zone, the events leading up to totality appeared like in slow motion. So I watched everything rather calmly without haste even though this was my first total solar eclipse
The following table describes the key events before 2nd contact C2 and after 3rd contact C3
C2 -
4m:18s Shadow bands on
1:34 First baily bead (kind of gap)
0:29 Many beads
0:17 Shadow bands fading out
0:10 Corona readily visible
Totality C2= 08:14:00 C3= 08:14:19
C3+
0:07 Shadow bands on
2:14 Shadow bands off
Photographs through a telephoto lens f=270mm without filter were taken between 08:12:30 and 08:14:20.5 just after 3rd contact.
They were digitally combined, click on the image for an animated view.
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| digitized Kodachrome 64 slides |
Shortly after totality all team members gathered at the farm and we exchanged our experiences and celebrated success. It turned out that the southernmost team was actually just a bit outside the totality zone. The friendly farmer’s family invited us for coffee and while talking we learned a lot about Oregon farm life (also about ownership of farmland by big companies like Boeing).
On the way back, we took took the route through the Warm Springs Indian Reservation and Portland where the sky was cloudy again. Needless to say – Corvallis had been clouded out for the eclipse in the morning. Upon return in the evening, the sun was shining and the first sign of spring was in the air.
Photos by Robert Hall, 8" Schmidt-Cassegrain
The coordinates of the observing site had been precisely measured by a professional surveyor in our team. Bob Hall took care of collecting all the observing records and doing pre-reductions before turning them in to the IOTA/USNO. His assessment of station 1+2640: ”This station has good timing data and good observations of shadow bands.” Later in spring a physics colloquium was devoted to the eclipse where everybody could show their pictures and exchange experiences.
References:
Bryan Brewer, Eclipse, Earth View, Seattle WA, first printing Nov. 1978.
Post Scriptum
Old data versus current state of the art computational tools:
Xavier Jubier's
Local Circumstances Calculator
David Herald's
Occult 4.0.9
C2 was at 08:14:00, sharply coinciding with the WWV time signal, i.e. 1.5 or 1.0 sec later as calculated nowadays.
The duration of totality was 1 or 2 sec longer.
