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At our obserservation place near Metz, France, (6.197 east, 49.222 nord) we have had bad luck with the weather. Lots of my planned observations and measurements were impossible because of nearly completete cloud coverage.
Contact times, calculated with AstroWin
11.08.1999 12:29:02 MESZ (= UT + 2h): Total eclipse 102.9 %
Sunrise 6h20m, sunset 21h 0m in Metz ET-UT = 63.7 sec
h m s Pa north Pa Zenit Azimut Elevation
1. Contact: 11.08.1999 11:09:18 284 318 124 44
2. Contact: 11.08.1999 12:27:55 104 123 150 53
3. Contact: 11.08.1999 12:30:13 287 307 151 53
4. Contact: 11.08.1999 13:51:33 107 103 185 56
My measurements in Metz, France:
The fat yellow curve shows the brightness of the sky. The red graph shows the temperatue (°C), the blue graphs are showing the wind speed (m/s, both left scale).
As there are rapid changes in wind speed, the bold blue graph is the average speed for the previous 10 minutes.
Because of the clouds we got heavy changes in the brightness
sky even before the eclipse began. During the eclipse, the temperature
dropped only by 2.5 degrees. Without clouds, we would have
expected a greater
Soon after 3rd contact the clouds got more transparent with little gaps until the 4th contact. This can be seen very good in the yellow brightness curve. The influence on the temperature was a rise from 15.5 to 19.5 ° C. I suppose, that half of this effect was influenced by the increasing solar crescent, the other cause seemed to be the decreasing cloud coverage. Note, tha our subject feeling pretended a stronger fall than our objective measurements. The temperature sensors in our skin seem to be influenced by solar radiation still if clouds obscure the sun!
During the totality the sky brightness sunk down to a value, which is comaparable to a solar elevation of about 6 degrees below the horizon. This is about 10 times more than full moonlight.
Sky brightness at totality:
Because of a failure of my registration software some measurents near the 3rd contact are missing. I took those values from the decreasing part of the curve near 2nd contact, as brightness should run symmetric to the mid of the eclipse. These interpolated values are marked by the thin curve.
The brightness dropped from 6.8 Lux at second contact down to ca 2.4 Lux at maximum of totality.
The wind near the ground seemed not to be influenced by the eclipse. In the beginning (at 9 h) it came from north-west, after the first contact it turned to north- north-east. The windspeed increased steadily in the morning.
In spite of this observation the movement direction of the clouds seemed to reverse after totality! In the beginning, clouds moved from north-north-west, after totality they moved from south or southwest. Perhaps this effect may be pretended by lower stage clouds, vanishing after totality. The middle stage clouds might have moved even before totality from south whithout being noticed at that time.
Interesting is the comparison of my measurements from Metz/France
gained in Haltern/Germany
(my Home, 7.18° E, 51.75° N).
11.08.1999 12:30:38 MESZ: Partial eclipse 94.0 % (93.2 % area)
Sunrise 5h 9m, Sunset 20h 3m in Haltern; ET-UT = 63.7 sec
h m s Pa North Pa Zenit Azimut Elevation
1. Contact: 11.08.1999 11:12:24 280 310 128 44
4. Contact: 11.08.1999 13:51:06 111 107 186 53
Day of partial eclipse in Haltern/Westf.
Here were predominating scattered cumulus clouds. At maximum the sun was obscured by some clouds. As the brightness sensor is placed within the city, nightly clouds cause higher brightness compared to clear skies.
Temperature: thin red curve, left scale (°C)
Brightness: bold orange curve
Vertical lines at Sunrise, 1st and 4th contact and sunset.
The eclipse day in Haltern was characterised by scattered cumulus clouds. The eclipse was partial with 93 % maximum coverage of solar disc area. It became notably colder and darker. In addition to this eclipse effect, clouds obsured the maximum eclipse, so that the sky brightness dropped down to one hundreth of a noon. But it remained still 20 times brighter than light intensity at sunset.
You can downlod my tables with the original measurements:
sofi_messung.zip, 13 kB zipped,
unzipped you get CSV-files, ready to import into any speadsheet software like Excel or similar. For obtaining Lux intensities, multiply sensor frequency with 0.0062.
Material and method:
My combined wind and temperature and brightness sensor.
The measurements were stored on a notebook-PC at my observation site. In Haltern i have a fix mounted weather observatory working on a C-Control-Unit of Conrad-Electronic. Once a day, the stored tables are saved on a PC's hard disc.
The sensor is the circuit "TSL230" (Texas Instruments), which converts light intensitiy to a frequency. It is mounted under a diffusor dome. The circuit can be varied in its sensitivity by canging the sensor chip area by a factor of 10 or 100. Additionally, the output frequency can be divided by 2, 10, or 100. So you get by simple adjustmend settings a dynamic range of more than 10^4. The output frequency can vary from < 1 Hz up to > 1 MHz. So it is possible to use one sensor for measuring light both at day and night. As the output is TTL-level, you can connet the circuit directly to the PC's parallel (printer) port or the input ports of the C-Control unit. The mesured frequencies are computed and stored in a standardized manner due to senitivity and output division settings. These values are stored in the downloadabel CSV-files. For obtainling intensities in Lux multiply with 0.0062 (accurancy +- 20%).
Near totality i took some measurements with high time resolution (10 ms), in order to quantify shadow bands. Unfortunately the clouds made these registration useless.
Temperature reagistration was done in Metz by the circuit "LM 75" (National Semiconductors). Its resolution is 0.5 ° C. (unfortunately i did not get the more precise DS 1621 in time :-(.
The temperature can be read via a two wire line interface (I2C bus) directly and digitally by the PC.
In Haltern the C-Control-Unit reads an analog KTY 87-205 sensor. The resolution is 0,9 °. Tthe sensor is mounted on a roof in the city (height 10 m). This is a possible reason for high temperature changes parallel to changes of sunshine.
The anemometer had three hemisperic shovels. Its rotation speed was registered by a light barrier with an accurancy of about 20 %.
All these sensors were mounted in Metz on a mast ca. 4 m above the ground.
This report originates Joachim Dräger's call for a coordiniated eclipse observation.
© 1999 Dr. Wolfgang Strickling.
back to Wolfgang's Astro-Homepage
Tables with measurements, sofi_messung.zip, 13 kB zipped
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Last update of this page on 13.09.2017