Attila reports that such strangely distorted solar disks can be seen almost every day in the exhausts of smokestacks. So it is worth while trying it by yourself to get a live impressions of physics.
At sunrise during the transit of Venus on June 6, 2012, there were not only distortions of Sun and Venus visible as well as the Green Flash, but there were also several observations of the so called Etruscan Vase.
As weather forecasts for Germany´s sunniest island, Fehmarn in the Baltic Sea, were most favorable for that day, Jens Hackmann flew there from the bad weather of his home town Bad Mergentheim. Just after sunrise at 4.41 hours, he observed the mirage effects mentioned above not only on Sun and Venus, but also on a passing ship. And only a few moments later the Etruscan Vase phenomenon appeared, an upside-down mirage of the sun which appears in most cases above a water surface (more pics and film).
Thomas Stemmler photographed the transit of Venus at beach on the Baltic Sea near Dahme and could shot mirage effects and the phenomena of Etruscian vase also.
This strange effect is caused by the refraction of sunlight together with a lower mirage and appears when a layer of cold air is positioned over a warm water surface. The lowermost air layer, which is heated up by the warm water, has a lower refraction index than the air at the level of the eyes of the observer. Sunrays hitting this layer in a very sharp angle can be reflected totally. So the observer does not only see light coming directly from the sun, but also light that had been reflected by the warmer and less dense layer of air directly above the water. The rays coming directly from the sun let the sun appear totally normal. But as our brains are not programmed for totally reflected sunrays, they extrapolate them lineally. This makes us see an upside-down reflection of the sun beneath the real sun which changes due to the angle of incidence of the light and thus with the sun elevation.
This phenomenon reminded the science-fiction-author Jules Verne of a paunchy Etruscan Vase standing on a pedestal, so he coined this term for the phenomenon.
On June 06, 2012, the rare constellation of the planet Venus crossing through the solar disk could be observed from the day side of the earth.
When in Germany the sun rose, the Venus transit was already in its final stage. Where the sun passed through differently dense air layers during its rise, the mirage phenomenon was visible, i.e. the sun as well as Venus appeared distorted or as a combination of multiple images. These effects are due to the different bending of the light waves at air layers of varying density. Moreover, an incident ray of light will be reflected at the interface between cool and warm air. When there are more than one of these interfaces, multiple reflection might occur.
Rico Hickmann could even observe the Green Flash during the Venus transit from Dresden: “I was incredible lucky with respect to the weather. Yesterday evening, it was still very cloudy, and after the end of the transit there were again clouds filling the sky. Before sunrise, a light pillar could be seen, that served as a pointer towards the sun. The sunrise over Dresden was spectacular, Green Flashes and disconnected segments… I’m still speechless.” Here are some more incredible pictures from this series: 1–2–3–4–5
Another spectacular image of a triple Venus was obtained by Frank Killich, who observed the Venus transit from the Wolfswarte in the Harz mountains (916 m / 0 °C). The image is a single frame from a HD video file.
Some more and equivalently wonderful observations were reported. Alexander Haussmann made a Video showing a triple Venus, green segments and distorted Venus passing through different air layers that were responsible for the green segments some seconds before. Further examples of impressive green flashes are the pictures of Andreas Möller, taken in Zinnowitz (photo and and animation as gif or MP4 [better quality]) and Hermann Koberger from Fornach, Austria (1–2–3).
On December 26th I climbed the 1000m high Plettenberg to observe and photograph the setting sun with 1m focal length to look for the green flash. The transparent air and an inversion layer were promising, however a few clouds with their top at approximately the same altitude were disturbing. The upper limb of the sun turned out to be quite turbulent showing green rims and flashes, but also some blueish apparitions.
Why a blue flash?
A green rim of the setting or rising sun occurs due to differential refraction in the atmosphere. If conditions are extremely clear, also the blue light has a chance to get through, and there might be even a blueish rim. With a temperature inversion layer in the atmosphere, upper segments of the solar image might get separated from the rest of the solar disc. In the final moments of these elusive segments they do appear green and sometimes even blue (green or blue flash). However, it is not clear to me why in my observations both happens. Most last moments are green, whereas the third frame shows a blue color and at the same time other turbulent segments with a green color. Should not every segment turn from green to blue, at least in the very last visible moment?
Maybe something more than just clear air plays a role for a blue flash visibility!?
It is the first time I see green and blue flashes simultaneously in one image. I strongly encourage other observers to record video data to show these effects in higher time resolution.
Author: Till Credner