Every now and then, you get a once in a while event like getting a Royal Flush while playing poker (about once every 650,000 hands of Texas Hold’Em). Even rarer are the once in a lifetime events like watching humans land on another world such as the Moon or Mars (soon!). And if you’re very lucky, you get to witness a once in a millennium event that comes down to pure chance. Like seeing the side of a mountain collapse.
This Astropoatmus one of those “once in a lifetime” events in late July of 2020 when the International Space Station, Comet C/2020 F3 (NEOWISE), and the Big Dipper all appeared in the northern sky at the same time for about 90 seconds.
This image shows the Big Dipper, the comet, and five streaks of light that came from five separate 10 second exposures of the ISS. While it may sound like cheating to composite these all together into a single image, this is what you would have seen if you had been standing where I was when the picture was taken (though the ISS would have been a moving dot of light, not a streak).
While the Big Dipper is out every night (at least in the Northern Hemisphere) and the ISS may travel overhead multiple times in a night (with possible weeks or months between visits over the same area), NEOWISE is a little different. It won’t be back in these parts again for about 6700 years. Give or take a few decades, that will be pretty close to 9000 CE, which is about as far away from us in time as the Little Gem Nebula (NGC 6818) is in the constellation of Sagittarius. Add the odds that the ISS is still flying around the Earth and in the same field of view as the comet and the Big Dipper in 6700 years and this picture may well represent a once in a million year event.
Sometimes, astropotamuses are just lucky.