Venus as a ring – how can that be?
During the last days several customers have sent us some very interesting photos of Venus, which we do not want to withhold from you. They show the planet as a very narrow sickle or even as a ring. This effect can only be seen on Venus by observers on Earth, and it is only visible when Venus is in lower conjunction (www.wikipedia.org/Aspects_of_Venus), i.e. when Venus is located between the Sun and the Earth..
How does the effect come about?
The planets Venus and Mercury are the only two so-called "inner planets": They are closer to the Sun than the Earth and orbit the Sun within the Earth's orbit. That‘s why they are the only planets that we can see a part of their surface which is not fully lit by the Sun. In the course of a year, they show phases just as the Moon does in the course of a month. On the other hand, we see all other planets always almost completely illuminated, because we look at them from the same direction as the sunlight shines on them.
The phases of Mercury are quite similar to the phases of the Moon. Venus, however, shows us something unique: The thinner the crescent becomes, the more the tips of the crescent overlap until it forms a complete ring on one or two days in some years. The reason for this is the atmosphere of Venus.
Venus is about the same size as Earth, but its atmosphere is many times denser. Every atmosphere is also an optical medium and refracts the sunlight. If Venus - seen from us - is exactly between the Sun and the Earth, then the Venusian atmosphere refracts the light of the Sun behind it just like a lens and sends it towards the Earth. The thin crescent of Venus becomes a ring. Since the orbits of the planets are not absolutely uniform, in most years Venus is too close to the Sun or too far away to observe the effect during the lower conjunction in the Earth's sky. Very rarely it even passes directly in front of the Sun, then there is a so-called "Venus transit".
This year, however, we are lucky that the Sun and Venus are about 2 degrees apart at the lower conjunction, which makes it possible to image the planet as a ring – but only for VERY EXPERIENCED amateurs with appropriate professional equipment. This is not a task for beginners! Working in such close proximity to the Sun without a solar filter carries the risk of accidentally getting sunlight into the telescope, which leads to immidiate blindness when used visually! We therefore advise against trying this at home – just enjoy these rare and interesting astrophotos and the stories they tell.
The following texts (partly in extracts) and pictures are directly from the respective authors and have been made available to us in german language. We translated them for your convenience and would like to thank the authors very much!
Venus with Baader Herschel prisma
by Dr. Sebastian Voltmer
Since February 2020 I have been documenting Venus regularly with my C11 EdgeHD and the Baader FFC Flatfield-Converter. Before each image session I recorded RGB data with my smartphone and shared a live image of Venus on Instagram (@sebastianvoltmer), which delighted fans of planets every time, since only a few have the opportunity to see a Venus crescent in the daytime sky.
Of course, the extremely close lower conjunction to the Sun on June 3, 2020 was especially exciting! Overlapping horns showed up already about 10 days before. But since the Sun shone into the telescope tube, the contrast was not optimal. An improvement was possible with a self-built mask, which casts a shadow onto the telescopes front. This also reduced the local seeing in the telescope tube noticeably. I could increase the sharpness even more by wrapping ice bags around the tube. An almost complete Venus ring formed three days before the conjunction, which is caused by the backward-illuminated Venus atmosphere.
The sunlight already hit the main mirror, but fortunately (under constant control) the light just missed the secondary mirror, so nothing was damaged. I could observe with the SCT in this way until the 31st of May. On June 1st, however, my reliable Astro-Physics Traveler telescope had to go in. A narrow Venus ring could be made visible with the 4"-refractor in the bright sky in close proximity of the Sun. The blue colour of the sky could be suppressed effectively with the Baader Red-Filter RG-610. When Venus was less than 2 degrees away from the Sun, the stray light from partly direct sunlight increased, so that it became a real challenge.
The high number of pollen in the air turned out to be a big problem. In the glaring light the image was full of bright spots caused by pollen in the air, so that Venus was seldom free of disturbing influences. Faint cirrus clouds in the predominantly transparent sky also made Venus disappear immediately from the picture. I thought about longer exposure times in order to create a motion blur of the pollen – the seeing was good enough. Then I had the idea to continue the documentation with a Baader Herschel prism. Due to the light attenuation of the prism in combination with an ND 1.8 filter, the exposure times of the video frames could be increased significantly and I was able to observe more reliably. Together with Venus I got ever closer to the Sun, up to 35 arc minutes - until the weather changed. This was the most extreme observation I could make thanks to the technical means.
After the difficult evaluation and processing of the video files and the hand-selected single images, it became apparent that the arc of light showed irregularities in the light intensity. Several planetary researchers responded to a shout-out in the social networks and expressed the assumption that these may be the result of local pressure changes in the uppermost atmospheric layer, which result in a different number of aerosols in the atmosphere of Venus. It is extremely fascinating to make such fine differences visible from Earth during the extreme proximity to the Sun.
Venus 55 hours before the lower conjunction
by Helmut Heinicke
Today (June 1st, 2020) I dared an experiment. The planet Venus was hurrying towards the lower conjunction, which it will reach on June 3rd at about 8 PM. Then Venus will only just miss the upper edge of the Sun. Its distance to the edge of the Sun will be only about 12 arcmin, i.e. slightly less than half the apparent diameter of the Sun.
I wanted to see if I would be able to catch Venus with its super narrow crescent a good 2 days before this lower conjunction. Of course, you must never look into the Sun without appropriate filters, but I want to emphasize this here once more.
Today at noon Venus was only 3.5° away from the Sun's edge. Only 0.21% of Venus were illuminated. This results in two difficulties: Finding the planet in the very bright sky close to the Sun, and focusing on the planet to see anything at all. Of course, both problems are interrelated: If the planet is not perfectly focused, you can't find it even if it is directly in your field of view.
Pointing the telescope to the planet is no problem for me nowadays. My mount is carefully polar-aligned, so that the "Goto" works perfectly. But focusing was more difficult than expected. Of course, it makes sense to focus on the Sun first. So I put a filter with Baader AstroSolar film in front of the lens and focused on the Sun. It is best to focus on sunspots - if there are any. And unfortunately, the Sun‘s disc was immaculate. So you have to focus to the rim of the Sun's disc. But that is unfortunately such a soft border. You can hardly recognize the really exact focus there - but that's what matters here.
So this is how I focused on Venus. When I was removing the solar filter, I looked into the tube from the front to see how far the sunlight reaches into the telescope and where there was still shadow – and I was satisfied, it was still safe. So I put an eyepiece into the focuser and looked for the narrow Venus crescent. But at first I couldn‘t see anything. Then I turned the focus knob slightly, and behold, now the super narrow crescent of Venus actually appeared. The pre-focusing at the Sun's edge was not enough for the sighting! But now the crescent was nevertheless very good to see. But a touch of the focus knob, and the crescent was gone. I looked at it at 140x magnification. I found that to be optimal.
Now it was time for the second part of the observation experiment: to record the Venus crescent with a webcam. Here again the focus problem is the biggest challenge. The focus position of the webcam is of course completely different to that of an eyepiece. So first back reattach the solar filter and back to the Sun to look for the focus at the edge of the Sun. This is not really comfortable on a laptop in bright daylight. Then point the telescope to Venus again. Thanks to a precise "Goto" this is fortunately the least problem. But on the screen I could not discover Venus for the time being. I tried to find the optimal setting of exposure, gain and gamma (gamma had to be quite steep). But only by turning the focusing knob I could finally catch the Venus crescent after many (!) attempts. By the way, what I noticed was that the air was full of pollen, which was constantly moving through the field of view. It looked a bit like rain. And there were also very bright and large pollen.
But I was a little bit proud that I could catch the Venus crescent so shortly before the lower conjunction.
I then tried to record the whole thing with an additional 2x Barlow lens. Doubling the focal length would have been a gain for sure for the extremely narrow crescent. But despite several attempts I unfortunately did not manage to find the right focus so that the narrow crescent suddenly "appears". With Barlow the problem was much bigger than without. In any case, I did not succeed in finding the crescent of Venus on the monitor with the Barlow lens.
The editing of the videos is also no piece of cake. Autostakkert, which I usually prefer to process planet videos, obviously could not do anything with the narrow crescent of Venus. The program always jumped over to the continuous pollen images. In the end, a useless image was created.
AVIStack has its strengths probably also with other motives. It did not get along with the Venus crescent. So only Registax was left, which I usually don't like to work with. But from this program I got a picture! This is what is attached. It is scaled to 300%. The about 1m of focal length is a little bit short. It would have been good if I had succeeded with the Barlow lens. In the original video the Venus crescent is only 2 pixels "wide". In nature, the crescent appears even narrower than on the photo.
But I actually managed to observe Venus visually and photographically only 55 hours before the lower conjunction. And that is something.
Venus in lower conjunction
by Bernd Koch
It was not easy to catch Venus safely with the telescope. First I put the AstroSolar solar filter on the 130mm refractor and aligned the telescope to the Sun. Then I pointed the telescope northeast towards Venus. So that this did not become a blind flight, I followed the movements of the telescope in the software Stellarium, until it reached Venus. Then I took off the solar filter and took a movie of Venus.
The disturbances visible in the image were caused by passing pollen glittering in the sunlight: some close and therefore blurred, some far away.
Please not: On the german AstroBlog on Schuelerlabor-Astronomie.de there are several more pictures and videos of Mr. Koch, which we could not take over all on our website. Please read the full story on the website, possibly with the help of Google Translate or a similar tool.
About the author: Michael Risch
Michael has been interested in astronomy and spaceflight, since he saw the last moon landing as a child. In 1981, he became a member of the Association of Amateur Astronomers in the Saarland and, as a member of the board, accompanied the establishment of the Peterberg Observatory. As co-founder and first webmaster of www.astronomie.de, he contributed numerous ideas and reports on astronomical and spaceflight topics to the first German astronomy portal. He has been practicing planetary, comets, solar, deep sky as well as TWAN style photography, and has been on many long distance trips, among others to 7 total solar eclipses. As a long-time science editor, he has led "Northern lights and stars" trips to the Arctic Circle. Michael has published many of his own photos and articles in professional journals and has written chapters for the books chapters for the books Fotoschule (Photo School) and Extremfotografie (Extreme Photography) with his colleague Martin Rietze for "Color Foto".
At Baader-Planetarium he is part of the observatory project team and is booked for lectures in Germany and abroad. Furthermore, he is an expert consultant for observatories, domes, high end mounts, telescopes and much more.