A bit late to the Venus party but I was on holiday with little kids...
Last Friday, the only close-to-conjunction weather window for Venus opened for us here in the South, where summer means cloud, wind, rain, wild temperature changes, more cloud, dust, pollen, crappy seeing - the list goes on. Not so on 7 January, with Venus just half a degree shy of closest apparent separation from the Sun on 9 January. Elongation was just under 5.5 degrees that day, a southerly flow had swept the sky clean for a few hours before the next load of cloud. This would have to suffice.
I figured altitude would help in more ways than one, so aimed for a midday session on high ground. I went to the Remarkables skifield just E of Queenstown, to a height of about 1,600m. There were heat plumes rising above the surrounding slopes, and wind gusts kicked some dust around, but the sky was dark blue and transparency excellent.
I set up the 8" Cassegrain and found Venus fairly immediately, at the expected location. 61° of altitude, nice. A gobsmackingly beautiful, razor-thin 270° arc in a steel-blue sky was immediately visible at 60x magnification, and the brain made it look like a full circle. This is bound to have been the view of the year for me. Yes, the year that's only 10 days old.
I had brought some cameras: ASIs 174, 178 and 462. Filters were the Astronomik 742nm longpass, Baader U Venus 350nm CWL and ZWO L.
The attached images give an idea of the visual appearance, as well as some idea of what was obtainable beyond visual.
Some notes:
- The dark area between the western end of the sunward half of the crescent and its cusp extension appears to be real (this was recorded by others around the time of this conjunction also)
- The crescent extends significantly further in the IR than the UV (the latter was hampered somewhat by the daytime seeing, and had to be recorded 2x2 binned to get exposure times down (see below), but that doesn not explain all of the difference to me.
- The sun-occulting contraption that was attached to the OTA, while absolutely essential, meant the setup was quite shaky. As a result, the two cameras with rolling shutters (178 and 462) struggled to produce an undistorted image with the wind, which was light throughout but never really absent. I found the processing of the resulting data a struggle and basically left the 462's images for another time. They did not appear to show more than the ASI174's either. That cam saved the day thanks to its global shutter.
- As with every Inferior Conjunction of Venus, I had wondered how complete of a circle might be detected, visually or otherwise. This was a wide one at more than 10x the separation of 2020's almost-transit. Well - some careful processing and hard stretching of the data appears to reveal what I'm inclined to interpret as a complete ring around the perimeter of Venus. This is the result of many iterations, during which I had found early on that placing alignment points in AS3 where one might expect to see something will litter that area with artifacts that the stretch will then reveal. This makes it impossible to tell what's real and what isn't, so I took care to limit all alignment points to the sunward half of the crescent. The result is a fairly smooth area against which a faint arc of light can be seen. Note how much fainter said arc is even compared with the directly adjacent farside crescent horns.
This has been a hugely enjoyable observation, despite its limitations. Not something I expect in the middle of summer.
what a fantastic write up and accompanying pictures.
And I'm not sure how much telescope work I'd get done with a view like that across the mountains. Incredible!
Fabulous results Mirko. View of the year and images of the year!
How far out was your occulting shield? Did you arrive at it’s size and distance by trial and error or did you do do the maths? I am very keen to try this next time. I think my closest observations of Venus have been at just the under 10 degrees so far.
Steve, I did do the math for the pole length, but seeing that this called for a ~2.5m length in front of the OTA I decided that was going to be impractical in the field. At home or at the observatory that may have been a different story. You could attach the thing to the dome and then move that, or a separate mount or something. Anyway the result was a 1.5m-compromise, where I added a curved lip to the cardboard shield I had used for the previous Venus shots from home 2 days earlier, which would end up taking a "bite" out of of the scope's aperture. I reckoned this reduction would mainly impact light grasp (not a big deal for this target) but much less resolution, since the full width of the primary was still clear along the other axis, and daytime seeing isn't that great to begin with. The size of the shield was arrived at by trial and error.
Thanks Markus, tracking was ok for what I needed to do. I established a N-S line using GPS, lined the mount up and set it to 45° and a bit South. That was enough to keep the target somewhere in the FoV for, dunno, an hour? I didn't really test that because the choppier wind gusts could flex it out of the FoV and back in in less than a second because of that long moment arm. So I did make minor adjustments more often.
