I recently spent a night imaging remotely at a dark site about 30 minutes from my house. When I started processing the results, I noticed a single frame that had the strangest pattern that I couldn’t quite figure out. The target was the Iris Nebula, and just about at the center of the frame there were star trails in concentric circles that almost look like the shot was taken at the pole. Except… it’s obviously not the pole, and there were other weird things going on like what looks to be a plane or satellite coming into the frame and then curving with the other trails. There were also some curves, like in the top left, that don’t seem to be on the same circular plane as the central trails. There were also what clearly looked like a standard satellite bombing through in a strait line on the left. Here’s the single 180″ shot with the trails, the only sub with this pattern:
Adding to the mystery, I also have an all-sky camera set up at my house that captured what surely must be an airplane circling overhead that same night. Here’s a video of that:
As I see this sub, I remember the odd circles from the all sky and figure that my image aberrations must have been caused by aircraft. I saved the sub in another folder, and went on to finish processing the final image. A few days ago, though, I came back to the picture with the nagging suspicion that something else was going on.
For one, what I dismissed as aircraft couldn’t possibly be aircraft. While I was shooting with my RedCat 51 at 250mm focal length, that’s still quite a tight bit of sky. There’s no way anything but a model airplane could maneuver in that tight space unless it was way up in the atmosphere. And the circles captured on my all sky that night were very wide paths… like half of the sky wide.
I posted the sub to the Astrobin forum to get feedback and with the sneaking suspicion that my original though was correct: there is an image at the pole somehow superimposed over what’s clearly an image of the area around the Iris. Most folks guessed camera rotation, but to me that bright streak seemingly coming into the frame before starting to rotate meant there was something else going on.
There was. I checked the timestamp on the sub, and turns out it was taken right at 5 am. That happens to be the time that Ekos tells my mount to park at the pole. Some folks on Astrobin guessed it even before I thought to check the time of the exposure. The camera started capturing a 180″ subframe, and then partway into it, the mount parked, slewing first in Declination, then in RA as it settled on the NCP. The large bright star isn’t departing… it’s entering. That star is Polaris, sitting right where it should off the shoulder of the Pole. Mystery solved.
In addition to the clean, final version. I ended up creating a version of that night’s exposures that included the fake UFO star trails. And now I have a reminder to check my parking times
Thanks again!