This page adds the latest image to the top, so for the whole story please read from the bottom of the page!
In the middle of October 2017, comet C/2017 O1 (ASASSN1) passed within about 0.72AU of Earth. This double capture from New Mexico and Spain was taken about 28 hours before closest approach: the weather forecast played a significant part in the choice of date.
Both images are stacks of 120-second subframes, and the time interval between the alignment frames was just 28 seconds.
Showing what might be possible, these two images are from the same 31-minute set, broken down into two sets of 15 minutes each and rendered as a GIF:
From the same session, this time through the telescope, these two images of C/2014 Q2 are separated by 31 minutes or 56,000km:
Trawling back through my archives I found similar possibilities. These two images of C/2014 Q2 are separated by 27 minutes – at 108,000km/h, the camera had moved 49,000km:
Following my presentation at the BAA Comet Section meeting on 17 June 2017, Dave Eagle picked up the idea and presented these two frames taken from the same location over the period of an imaging session. The Earth’s orbital speed of 108,000 km/h means that a much larger 3D separation can be achieved by a short pause than by using telescopes on opposite sides of the Earth – only 12,700km apart.
The follow up to the original proof of concept, this time in monochrome. Another simultaneous pairing with iTelescope in Mew Mexico and Spain, and comet C/2015 V2 more than 1AU from Earth. The 3D separation is only just visible:
This was the first successful proof of concept photo after several false starts, with two simultaneous exposures using iTelescope systems in Mayhill, New Mexico and Nerpio, Spain. Comet 41P was only a quarter of an AU from Earth, which was close enough to make the 3D separation clearly visible: