Reading a photo - manual astrometry
I was talking about wide-field images with a customer last year. Mal showed me a photo he'd taken while back "up north". He'd used a now-elderly Canon M3 mirrorless with a Samyang 2.8mm fisheye.
Mal told me that when he took this photo, he was in an area so dark that he hadn't noticed he was underneath a powerline until he previewed the photos on the back of the camera. You can see the lines go through the Small Magellanic Cloud. We both agreed that we enjoyed working in the dark. The bluish colour on the horizon is a car on a main road. That power pole provides a subject for the centre foreground. Without it, these photos get boring - just fields of stars.
The shot was less than 30 seconds at f/2.8. He'd set the ISO very high. The camera has a clever noise reduction system, which takes three "light frames" and one "dark". Noise measured in the dark frame is subtracted from the lights, which are then stacked, further reducing the noise.
This photo has a lot in it, apart from Mars, Saturn and Jupiter. I thought I'd delve a little deeper. Here are my annotations.
Mal was facing due south. If you know where to look, you can see Sigma Octantis above and a smidge to the left of the power pole.
I tried to date the photo by planetary location. There isn't any magic in this, I used Stellarium to watch Jupiter move over time. Based on the double star Zuben el Genubi, HIP 72489A, HIP 72640 and HIP 72194, I guessed 11 July 2018. This is the detailed area of Mal's photo.
After I asked Mal the actual date, I found I was wrong, it was 11 June 2018. Rookie error - I'd been foxed by Jupiter moving into retrograde and going back over nearly the same ground! You can see Jupiter's path in this Stellarium shot for 11 June. It had started on the left on the upper path, moved to the right, then stopped and continued back to the left along the lower path.
Incidentally, this retrograde motion of the planets was a huge and complex puzzle for earlier astronomers. Their study, and eventual understanding of this planetary behaviour led to our modern understanding of our solar system, and cosmology in general.
Once I knew the date I was able to estimate the latitude. The star due south, just visible to the left of the power pole, is HIP 31897, which has a declination of 80°49', but there are low hills there, complicating things. My rough guess put Mal at 15° South, and I had a stab that he was on Cape York.
Later on, Mal told me he was at Kununurra in WA. A miss is as good as a mile!