A huge see-through dark object appeared in one of my photos during an all-night time lapse I was doing.

I captured this in Flagstaff AZ near the peaks at 8000' elevation while doing a time lapse to capture Geminid meteors. I was there from 4pm 12-14 until 8am the next morning 12 -15. My camera was set to capture a photo every second (25 second exposures.) I was in my van sleeping when this happened. I only saw what I captured today after going through the images. I have taken tens of thousands of images of the night sky the past 8 years and have never caught anything like this before. Nothing like this appeared in any of the hundreds of images that I took on this night nor has it appeared before or since. The camera was near my van, and my dog in the van would have started barking if anything came near the camera or my van, and I also would have heard something. I have no explanation of what this was. Strangely, I saw or heard no animals on this night, and also not another human soul was seen the entire night. It was oddly dead silent. I have come here hundreds of times the past 10 years, and this was the first time that I captured this.