Last week, a seemingly spectacular astronomy video went viral. It was created by a German astrophotographer named Julian Wessel, and it showed the International Space Station passing directly in front of Saturn. I saw links to it all over Twitter and Facebook, and no wonder: Catching such an event takes an extraordinary amount of skill and planning. Plus, it’s just cool.

There’s only one problem: It wasn’t real.

Wessel used images from different observing sessions and composited them together to make the video and the image. Under some circumstances this is OK—for example, when different telescopes are used, or when you’re reconstructing a scene (like the Earthrise image taken by the Lunar Reconnaissance Orbiter). But in any case, the important bit is to note that it’s a composite.

Wessel didn’t do this; on his website he said, “I managed it [sic] to photograph the ISS in front of a planet again. In this case it was the Lord of the Rings: Saturn.” He also wrote, “Fortunately everything happened as planned and I could make the capture… You can see the Video of the Event on my YouTube… This is a great effort for me as an astrophotographer. It takes time, patience, preperation and a little bit of luck to get a shot like this, but at the end the hard work pays off!” That certainly makes it sound like he got footage of the actual event. He also submitted it to the Astronomy Picture of the Day site, which ran it (though, after review, they have since taken it down).

The video was convincing enough that it got past a lot of people. When I first saw it, I was amazed, but it also set my skeptic sense tingling. It bugged me that he happened to catch the ISS directly in front of Saturn in one frame of the video; the odds of that are pretty low. And it all looked too crisp and clean, but that wasn’t enough for me to declare it a fake.

However, not long after the video became public, a whole bunch of amateur astronomers were on the case. My friend Stephen Ramsden (who does solar observing) sent me a note letting me know that people were buzzing over some serious issues with the video. Also, Christopher Go, who is a phenomenal planetary astrophotographer, also pointed out many problems with the video. As a few examples:

The ISS should have been about twice as big as the disk of Saturn, yet they’re the same size in the video.

ISS is far brighter than Saturn, but they appear equally well-exposed.

Saturn should have been grainy looking, noisy, due to the very short exposure.

At the time Wessel claimed to have taken the video, the Sun had just risen. The sky should have been very bright, and Saturn would have been extremely low contrast, almost washed out by the bright sky. Saturn was also very low in the sky, and atmospheric distortion should have made it look very fuzzy.

It was very cloudy that morning at the location Wessel claims to have taken the video.

I could list many more issues; most are pretty technical and circumstantial, but it’s a long list.

I sent Wessel an email asking him some specific questions, but I did not hear back. Not long after that, he removed the entry about the video from his site and Facebook, and removed the video from YouTube (which is why I didn’t embed it in this post). He also posted to an astrophotography forum, saying the image was a composite, but that doesn’t jibe with the claims he made earlier, which purport it to depict the actual event.

I don’t know what Wessel’s motivations are, and I won’t speculate. I will note that others are looking at some of his previous work and calling foul on that as well. Update, Jan. 26, 2016: Wessel has posted in the APOD message board apologizing for what he did.

But I’m writing about this because I think it’s important to note that it’s easy to get fooled. Software is so good that stuff like this can be created pretty easily, and it can be good enough to fool people passingly familiar with astrophotography, at least at first (though generally not for long, as we’ve seen here). But for people who don’t know much about it, this kind of stuff gets believed, and passed around social media rapidly.

That bugs me for a couple of reasons. One is simply about the nature of truth: People shouldn’t create fakes and then claim they’re real, and if they do then it should be called out. But more, it diminishes the actual photographs, the actual videos, and the very very hard work astrophotographers put into their craft.

For me, I love to share the joy and wonder of the Universe, and when artwork or fakes or computer simulations get passed around as the real thing, it diminishes what’s really going on around us. I prefer to appreciate things as they are.

A lot of fake astrophotographs get shared on social media (especially by those spammy Twitter feeds with handles like SciencePorn and UberFacts, and usually with no links or credit to the original creator). I know a lot of people love seeing these pictures, but I think it’s important to separate fact from fiction. The Universe is actually and truly a stupendously gorgeous and astonishing thing all on its own. We can appreciate artwork depicting it, but we should also understand what’s real and what isn’t.

And here’s some irony for you. As I was drafting up this article, I got a note that Szabolcs Nagy was in fact able to catch ISS transiting Saturn on Monday in Gran Canaria! Here’s the video:

Yes, I checked, and this one looks real! It is possible to get this sort of thing on video. Like I said, it takes patience and planning, and maybe a bit of luck, too. See? Astronomy is really cool.

I suggest following FakeAstropix and PicPedant on Twitter to see if that viral pic you saw on Facebook is real or not.

I’ve also written about fake pictures many times. Here’s a selection:

But sometimes they are real: