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Measuring modulus During the eclipse we measured exposure and temperature by in advance constructed modulus, which designed and made Jiøí Hofman and Václav Šváb from the West-Bohemian affiliate of the Czech Astronomical Society. The same modulus used the second expedition in Angola headed by Dr. Markova from the Upice Astronomical Observatory.
The whole measurement by modulus lasted four hours, therefrom one hour before partial phase and one hour after it. From the reference reason the same measurement was made one day before the
eclipse. The modulus was placed on the special pedestal, which produced Mr. Jaroslav Petrovicky from the workshop of the Department of Physics, FEE CTU, and it was situated one
meter above the ground level.
During the both measurements it was a sunny weather with mild wind. The
measurements were carried out on the grass University playground in Lusaka. The
environment was open in all directions. The measuring place had coordinates:
latitude -15° 23' 42", longitude 28°19' 37"
(average value from 30 minute measurements by GPS), and altitude 1263 m. Contacts:
Results
The temperature (red curve) varied in the range of 2.5°C only. It is not surprising as the weather was sunny and the wind was mild and omnidirectional. The observation place was at the University playground in an open area. The exposure (blue curve) decreased gradually during the whole measurement.
The situation rapidly changed during the eclipse. The temperature varied in the range of 7.2°C and reached maximum at 2 p.m. local time. At 3.20 p.m. (local time) the temperature reached minimum value (17.8°C). It occurred 8 minutes after T3. The delay of the temperature minimum after the exposure minimum was 11 minutes. This phenomenon might be explained via the huge heat capacity of the land and the atmosphere. The exposure begun to decrease about two minutes after T1 and between T1 and T2 it decreased almost linearly. During the total phase the exposure decreased bellow measured value (zero value in the graph). After T3 the exposure was increasing but not to the original value before the eclipse because the evening was coming.
On this graph you can see the comparison of measured temperatures during June 20 and 21. While in the first measurement the temperature varied in the interval of 2.5°C (during 4 hours), during the eclipse it was 7.8°C.
Comparing exposure it is obvious that till T1 the curves are nearly identical. The exposure decreases linearly between T2 and T3 during the eclipse and after T3 begins to increase. However it doesn't reach the original value. The comparison curve decreases monotony as the Sun moves on the sky.
In Angola the temperature depletion is much more evident. The value 10.7°C is caused by longer duration of total phase in Angola. The temperature in Angola during the measurement was much more higher because the observation place was located only 11° south from the equator and furthermore it was near the coast and only 186 meters above the sea level. In spite of the sooner beginning of the eclipse, the temperature after the eclipse didn't reached the value before T1.
On this graph you can see the comparison of the exposure curves during the eclipse in Angola and Zambia. The slope of the curves between T1 and T2 is nearly the same in both cases. After T3 there is rapid increase and subsequent decrease of the exposure. It might be caused by the location of the observational place (4° north of Lusaka location) and quicker sunset. |
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