It completely disappeared from my memory who told me about the ISS Transit Finder page (I suspect my colleague Robert, because of his wide interests that include fascination with astronomy). The application allows the user to position in an arbitrary place on Earth, and find out if the International Space Station will orbit above the sky anytime soon. During the night, the ISS is easily visible with a naked eye, even from a large city. The station's orbital period is about 93 minutes, and the duration of a flyby spectacle in a specific location is counted in single minutes. While the passage of the station in my area happens quite often, its transit through the disk of the Sun or the Moon is much rarer phenomenon.
A transit is also a much harder phenomenon to capture than an ordinary flyby, because it lasts just about one second in the case of the Sun, and about half a second for the Moon. On the Internet, one can find a plethora of magnificent images that were taken with the equipment worth tens of thousands of dollars. For the most of us, such hardware is by far outside our price range. The situation might seem hopeless. When we are thinking about our old reflex camera, astrophotography is not the first thing that comes into our mind. And that is a mistake! It turned out that my entry level Nikon D3300 did quite well in combination with StarTravel 102 AZ3 telescope.
As I mentioned before, the ISS transit of the Sun lasts about 1 second; it was exactly 1,17 second in this specific case. This is why it is of utmost importance to set the time as precisely as possible on the device, which will be used as a time base for our photos. I chose my notebook and the NTP2 service set for the GUM time3. These servers are synchronized with the national atomic time standard. I also assumed that there will probably be some discrepancies between the GUM time and computations presented on the ISS Transit Finder website. It was also important to take into consideration that my camrea can take about 6 RAW photos per second. Once the cache is full, the speed of taking pictures slows down, because the data must be written to the SD card in order to free up space in the buffer. This effect actually occured, which is visible on the image in the increased distance between the two last positions of the ISS. Finally, I decided to release the shutter half a second before the scheduled transit time.
Success! Two of the six „fast frames”missed the ISS a little, but the remaining five were spot-on. The last one shows the abovementioned effect of camera cache filling-up and lengthening of the image capture process. The final image is a result of stacking six frames with the Siril software. In the close-up picture, we can see some of the shortcomings of my setup, but also almost certainly I had my part in it. A few minutes before the transit, I configured the setup and took some test photos. About two minutes before the flyby, a sudden thought popped in my head, saying that maybe I should readjust the focus… Less than a minute before the deadline, I was still fumbling with the focus knob, making adjustments in a haste and fear of missing the transit. I'm almost sure that I had worsened the previous settings, and as a consequence, the final image. Well, patience is something you supposedly can learn.
Here you can download the .tar.zst
archive
of six original images.
To extract it, you will need a program that supports the zstd archives.
I think that people with graphical skills greater than mine will be able to get
something more from them than I did. I'll be happy to see your work.