| Total Solar Eclipse of 11 July 1991, Introduction:
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| The total solar eclipse of 11 July 1991 was my second total solar eclipse. It was observed from Mazatlan, Mexico. Mazatlan was selected for budgetary reasons. A trip to Mazatlan including lodging cost less than half as much as an eclipse tour to Cabo, etc. The weather prospects were not as good in Mazatlan, but the probabilty of clear skies was still above 50 percent. The trip was short, so I did not get to take pictures of Mazatlan itself.
The only other total solar eclipse I had seen was on 26 Feb. 1979 in Montana. The lunar umbra had put on quite a show in 1979, and some of the best views were under circumstances I did not anticipate. For example, yellow and orange color was visible just below the leading edge of the umbra only seconds after totality began, and motion of the umbra boundary was obvious. Totality was visible through thin clouds in 1979, but it took a back seat to seeing the umbra move down toward the eastern horizon, eating up the the blue sky beyond as it went. Because it appeared that the umbra could put on a good show in almost any direction, I decided to take a series 360 degree panoramas at the 11 July 1991 total solar eclipse. These would capture the entire horizon, and thus any impressive effects of the lunar umbra, regardless of the time or direction. Each panorama consisted of four photos taken with a Nikon FM camera and a 16mm f/2.8 Fisheye Nikkor lens working at f/4. One limitation was film. Since each panorama required four pictures, I could only take nine panoramas. There was no time to change film. I ended up taking 12, with the final three being hand held with the camera body from my telescope. However, the first three were taken so early that the umbra made only subtle changes in the western sky. At this eclipse, the umbra was theoretically be detectable as long as nine minutes before totality in a clear sky. However, clouds in our area kept it from being visible until about five minutes before totality. Instrumentation consisted of a Vernonscope 94mm f/4 triplet refractor on an Aus-Jena equatorial mount, and a Sony TR-7 camcorder with a 3x converter, both for the corona. Wide angle cameras included a Nikon FM with MD12 motor drive and 16mm f/2.8 Fisheye Nikkor lens on my home made motorized indexing panoramic platform to take 360 degree panoramas. The motorized platform was built to facilitate taking each 360 degree panoramia in only 6 seconds, in order to minimize "time distortion" in the final image. Additional items included a Pentax H2 camera with a Soligor fisheye attachment mounted on an Argus 50mm f/3.5 Coated Cintar lens (from an Argus C3) via a custom T-mount cell. A borrowed Sony camcorder with a 0.5x wide angle attachment was pointed west to capture the approaching umbra. A Gossen Luna-Pro meter was used to measure incident light levels. The Eclipse Begins: The sun is in the clear when the partial phase of the eclipse begins at 10:32 a.m., but by 11:20, the sun is intermittently obscured by clouds. The clouds are a combination of high clouds through which it might be possible to see the inner corona, along with low clouds that are moving from the mountains toward the shore, though I did not know it at the time. It was not possible to distinguish between the two, but my all-sky pictures showed this was the case. By 11:45, 14 minutes before totality, the ambient light is clearly muted, and color on everything around us seems to be graying out. The exposure for ISO 125 film is 1/125 second at f/4. A few minutes later, the sky low in the west begins to darken a little. At 11:55, just 4 minutes before totality, the clouds are thin enough to see the shrinking crescent sun. It's dim, but well defined. It looks like we might get to see at least prominences and the inner corona. Ambient light now meters at 1/15 second at f/4. Darkness in the western sky is more pronounced and its width has enlarged to about 60 degrees, though it does not reach very far up into the sky. As it slowly grows, it widens more toward the south than toward the north, since we are situated well north of the eclipse center line. By two minutes before totality, the umbra is obvious to everyone as it dominates the western and southwestern sky. The trailing edge of the umbra soon clears the western horizon, revealing returning sunlight beyond as a muted orange color. With only one minute to go before totality, motion of the umbra is obvious as it covers a cloud bank well to the southwest, while also being visible on high clouds beyond. A pale yellow color illuminates distant clouds immediately in front of the umbra. To the west and southwest, color beyond the trailing edge of the umbra is becoming a more saturated orange color. A few seconds later, umbra is so large I cannot see it all at once, but I can still tell it is getting larger. We are being engulfed, and it is exciting! At 11:58:25, totality is only 20 seconds away. The crescent sun is still visible, though it is less defined. Ambient light is dimming as fast as lights in a theatre before a movie, and the sun begins to look like an indiscinct spot of light rather than a crescent. Its light becomes harder to see, then it simply disappears into the gray clouds overhead. Apparently, the clouds are too thick for seeing the corona, and scattered light from outside the umbra makes the clouds look dark gray instead of black. The ground looks dark, but not black. Ambient light now reads 3 seconds at f/4 on the meter. Meanwhile, color at the distant leading edge of the umbra has become a fairly saturated mixture of yellow, orange, and even red light. We are now in the moon's shadow. And so, we didn't see the corona. But the lunar umbra put on an excellent show, as you will see in the 1991 eclipse panoramas below! © Copyright 1991, 1997, 2017 Jeffrey R. Charles, All Rights Reserved. |
| TOTAL SOLAR ECLIPSE OF 11 JULY 1991 | ||
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| 360 DEGREE PANORAMIC PHOTOS OF THE LUNAR UMBRA © Copyright 1991, 1997, Jeffrey R. Charles, All Rights Reserved. | ||
| The following sequence of panoramic photos show the dramatic approach of the lunar umbra. Each panorama covers about 90 degrees vertically by 460 degrees horizontally (for about 100 degrees of horizontal overlap). The directions North, East, South, and West, all appear immediately below each panorama. The hotel building to the North appears twice; once at each end of the picture. | ||
| Additional information is shown under the directions: | ||
| Local time (hh/mm/ss) is shown under the center of each picture. | The time before or after second or third contact is shown under "West". For example: "2C-3:14" is shown under the first panorama, indicating that it was taken 3 minutes, 14 seconds before the beginning of totality. | The exposure time and f/ratio is shown under "North" on the the right side of each panorama. The first six panoramas were taken on Ektar 125 film The last three were taken on Kodachrome 64. |
| Each panorama is made up of a series of four photos taken with a Nikon FM camera and a 16 mm f/2.8 fisheye Nikkor lens. The North photo is repeated at each end. In order to facilitate taking panoramas in an expeditions manner during the eclipse, Jeffrey R. Charles designed and fabricated a remote control indexing rotary camera platform. This allowed each panorama to be taken over a period of only six seconds. | ||
| The panoramas were taken for aesthetic and data collection purposes. The data is used to determine the altitudes at which the boundary of the lunar umbra is most prominently projected on the earth's atmosphere. This information is used in predicting various umbral phenomena which may be visible at future total solar eclipses. | ||
| A dozen or so panoramas were taken at the 1991 eclipse. The best nine are shown here. Even though local clouds obscured the corona, it was clear several kilometers out to sea. The clear western horizon allowed the umbra to be detectable nearly ten minutes before totality, but its appearance on a panorama was insignificant until within five minutes of totality. Accordingly, this panoramic series starts at just over three minutes before totality. | ||
| The Lunar Umbra from Mazatlan, Mexico © Copyright 1991, 1997, Jeffrey R. Charles, All Rights Reserved. |
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| Above: The Umbra Approaches Mazatlan, Mexico Ektar 125 Color Negative Film, Exposures as Shown. The TOP 360 degree panorama shows our surroundings a mere 3 minutes and 14 seconds before totality. The lunar umbra is a wide, slightly darkened area low in the west. CENTER: By 1 minute and 42 seconds before totality, the approaching umbra is obvious to everyone as it grows in height and width. The trailing edge of the umbra is about to clear the western horizon. BOTTOM: Only 57 seconds before totaliy, in the leading edge of the umbra visibly moves over a clound bank toward the south. Faint yellow color appears beyond part of the distant cloud bank. © Copyright 1991, 1997, 2017 Jeffrey R. Charles, All Rights Reserved. |
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| The Umbra Engulfs Mazatlan, Mexico Ektar 125 Color Negative Film, Exposures as Shown. TOP: Only 20 seconds before totality, the umbra is over 120 degrees wide and its circular shape is visibly projected onto high clouds. Yellow color is below the umbra's trailing edge to the west. CENTER: One minute and 41 seconds after the beginning of totality, sunset colors are obvious around much of the horizon, but it is still relatively bright toward the southeast. BOTTOM: By 3 minutes, 51 seconds after totality began (1 min, 25 sec. before totality ends), the south and east are darker. Sunlight beyond the umbra's western trailing edge is brighter. © Copyright 1991, 1997, 2017 Jeffrey R. Charles, All Rights Reserved. |
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| The Umbra Departs Mazatlan, Mexico Kodachrome 64 Color Slide Film, Exposures as Shown. TOP: By 22 seconds after totality, immediate surroundings are brighter and the shape of the umbra is again visible as it moves toward the southeast. CENTER: By 41 seconds after totality, the umbra looks a lot smaller, but its shape is still obvious. BOTTOM: Little trace of the umbra remains by 2 minutes, 15 seconds after totality. This is partly because of thick clouds to the east. The last trace is darkening in clear sky to the southeast. © Copyright 1991, 1997, 2017 Jeffrey R. Charles, All Rights Reserved. |
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| All-sky Images of the 11 July, 1991 Total Solar Eclipse. © Copyright 1991, 1997, 2017 Jeffrey R. Charles, All Rights Reserved. |
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| LEFT: All-sky image taken only a few seconds after totality began at the 11 July, 1991 total solar eclipse. Clouds cover most of the sky. The sun was near the zenith, but low clouds obscured it shortly before totality. High clouds above the low clouds made the lower clouds hard to see. The low cloud is visible here because it is illuminated by light reflected back into the umbra from the southeast, which is to the upper right. The large umbra at this eclipse covers much more sky than usual. The thin line of yellow-orange at the extreme left edge of the image is sunlight just beyond the trailing edge of the umbra. Equipment is a Pentax H2 film camera and a Soligor 0.15x fisheye attachment affixed to a 50mm Argus lens via a custom T-mount cell. Exposure is 1 sec. at f/6.8. RIGHT: All-sky image taken two minutes after the end of totality. The umbra is just a small, dark area low in the southeastern sky. North is at the bottom in both images. |
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| Instrumentation | |
| Motorized Indexing Rotary Camera Platform © Copyright 1991, 1997, Jeffrey R. Charles, All Rights Reserved. |
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| This custom indexing rotary camera platform was used to take the 360 degree eclipse panoramas in this article. The left photo shows the platform with its remote hand control. The shutter release wire (attached to the camera) unwinds from the tripod column as the platform spins. It was subsequently replaced by commutators. The top right photo shows the top of the platform. The bottom right photo shows the top section of the platform close up. The platform can easily be configured to stop at predetermined intervals of 30, 45, 60, 90, 120, and 180 degrees, or to stop at any pre set combination of these angles. |
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| Use of material herein is subject to conditions in the Versacorp Legal Information Page. Need information about eclipses for your planetarium, motion picture, or other project? Jeffrey R. Charles performs science consulting in regard to eclipse phenomena and instrumentation. Please direct inquiries to Jeffrey R. Charles (jcharles *at* versacorp dot com) or visit the Versacorp web page (www.versacorp.com) for more information. |
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© Copyright 1991, 1997, 1998, 2017 Jeffrey R. Charles, All Rights Reserved.
Uploaded to this domain: 18 Feb. 1997 |