Sirius scintillation

Caused by the numerous cities and industrial areas south of my observation site (North-Rhine Westfalia, Ruhr Area, Germany), there are rather strong air turbulences (bad seeing) near the horizon. But what is bad for astronomical photographs, however, can be very nice to demonstrate atmospheric aberration and dispersion in the star trails on photographs without tracking. The lower a star is in the sky, the more pronounced is this effect, especially at very bright stars.

In this case, Sirius had an elevation of 11° on October 23, 2011, at 3.10 hours. The sky was clear, wind was at 1-2 Bft, temperature 3°C and humidity at about 80%.

I took this photograph using a Canon EOS 350D, which was focally adapted to a Maksutov (6”, 1800mm, f 12,0). After having been adjusted and properly focused, the telescope was driven at maximum speed over the right ascension axis. This makes the star transit rapidly through the field of view causing a star track on the camera chip which records the chronological sequence of the flickering of the star.

Author: Ronald Blendeck, Germany

Ozone makes twilight wedge blue

Normally, the twilight wedge appears in a rather grey colour. But sometimes, in most cases above an inversion layer, the twilight wedge appears tuquoise-coloured as during this morning twilight on March 2, 2011. The night before had been so clear that the zodiacal light was visible for the naked eye. Towards the sun, above the first light of dawn, the crescent of the moon and Venus made a nice contrast to the blue sky. On the opposite side, there was a definite twilight wedge showing a rarely clear blue colour. This colour is caused by light absorption in the ozone layer.
Above the twilight wedge there was also the venus belt visible. (Photos 1 – 2 – 3 – 4)

Author: Claudia Hinz, Brannenburg, Germany

Total Lunar Eclipse on 16th June 2011

On June 16th, 2011, a total lunar eclipse, centered on the Indian Ocean, was visible from Europe, Africa, and Asia. The photo shown above was taken a short time after moonrise by Wolfgang Hinz in the Bavarian Alps, Germany.

Further pictures sent Pitan Singhasaneh, taken in Bangkok, Thailand, where the total phase happened just before the Moon set.

The eclipse was quite dark in all regions of visibility. Therefore, the Moon was only seen as a feebly lit reddish-brown disk during the never quite dark late summer evening hours in central Europe. The remaining illumination on the Moon is due to light refracted into the Earth’s umbra in different layers of its atmosphere, and therefore bears the imprint of the red-orange color of the skies at the Earth’s dawn or dusk terminators. Because the Moon travelled almost right through the umbra’s center, this eclipse had a very long duration of totality (101 minutes) and consequently became quite dark in the innermost parts of the umbra which only get light from the lowermost and thickest layers of the Earth’s atmosphere. Additionally, the atmosphere was contaminated by dust from three volcanic events in Chile, Iceland, and Ethiopia which might have further diminished the illumination of the eclipsed Moon.

Elmar Schmidt did photometry on the Moon at Farm Hakos in Namibia at 1834 m altitude. The darkness of the eclipse was quite pronounced even under the excellent skies of Namibia, where the Moon climbed to an elevation of more than 50 degrees during mid-totality. Then, a pair of 10×40 binoculars did not show the contours of the lunar maria at the brownish grey center of the Moon’s disk. On the other hand, the eclipsed Moon always retained a generally deep orange color. Its minimum brightness of -0.35 visual astronomical magnitudes complies with an extrapolation from less deeper eclipses, thus not really pointing to a significant influence of volcanic dust. An exception could be taken with respect to the asymmetry of the eclipse which was much darker at the exit as compared to the ingress – although more colorful because of showing the blueish-green tinge at the umbra’s rim. This might hint to darker or altered atmospheric conditions near the Earth’s eastern terminator over the Indian Ocean and Western Australia.

Authors: Claudia Hinz, Elmar Schmidt

Perigee Moon

This photo was taken by Claudia Hinz at the evening of Jan. 11th, 19.35 CET from Mt. Wendelstein (1838m), Southern Germany. The full Moon in this night was extra bright. Dr. Elmar Schmidt of the SRH University of Applied Sciences in Heidelberg, Germany, used an absolutely-calibrated photometer to precisely measure the moonlight and found it more than 50% brighter than that of a typical full Moon.

1. The Moon was at perigee, the side of the Moon’s elliptical orbit closest to Earth.

2. The Earth-Moon system was near perihelion, the side of Earth’s elliptical orbit closest to the sun. Extra sunlight increased the reflected luminosity of the Moon.

3. The Sun-Earth-Moon trio were almost perfectly aligned. This triggered a strong opposition effect an intense brightening of the lunar surface caused by the temporary elimination of normal shadows.

4. The weather conditions were optimal for photometry due to the clean and dry arctic air (its relative humidity being less than 10% at the moment of the photo). This resulted in only clear air scattering of moonlight with no extraneous glare as evident in the completely blue night sky. The brightness of the mountain landscape was additionally increased because of the reflection from the snow.

Elmar Schmidt details the relative contributions of each factor in his full report.

Authors: Elmar Schmidt & Claudia Hinz