To the left you'll find "The Crucifixion." The image on the bottom is the 14th century fresco at a monastery in Kosovo, and it bears some interesting details, which I have enlarged above the original painting. According to ufologists like those on the Ancient Aliens TV show, these odd looking figures in stranger looking objects are extraterrestrial beings piloting spacecrafts. In fact, from my observations, this is one of the most frequently cited examples for the claim that aliens have visited the earth since ancient times. After all, what else could these little men in flying contraptions be?
Before I deconstruct this argument, take a moment to think about what we're being asked to believe in the suggestion that UFOs are depicted in this artwork. Why would a medieval Christian artist put two alien spaceships on either side of the crucifixion of Jesus? If the answer is that aliens were at the crucifixion, that's preposterous nonsense without a shred of any evidence, and this is a fresco created over 1200 years after the death of Jesus, so it couldn't exactly constitute any sort of historical record. If your answer is that the artist had encountered UFOs and wanted to put them into one of his creations to subtly tell the world, then we have yet more presumption, but also a question that ufologists never are willing to answer. Why the crucifixion? Why wouldn't the artist have simply composed a separate work of art depicting these alien spacecrafts? Furthermore, if this fresco was commissioned by the church (as most medieval church artwork was), then was the church in on it too? If not, why would they have allowed such foreign material into a depiction of their lord's suffering?
The short answer is that these details are not UFOs. In crucifixion scenes of the medieval ages, it was fairly common practice to represent the sun and moon as witnesses to the death of Christ. If you look closely at the details in the fresco, you'll see that the one on the left is an orange hue with spikes coming off it in a way that makes it look like a fireball. The object on the right is a blue or silvery hue and does not appear to have the flame trail of the other one. Thus, the craft on the left is the sun and the craft on the right is the moon. But why the human-looking "pilots"? Again, this was a common practice in medieval crucifixion art, to personify the sun and moon. We find another example of this in Antelami's crucifixion scene, Deposition from the Cross. If you click the link, you'll notice the sun and moon at the top corners of the frame, with a human face in them. As further confirmation that this is what they are intended to be, you can read the words "Sol" and "Luna" next to them, which are Latin for sun and moon.
As someone who's grown up watching and reading a lot about UFOs, I have to say that if anything can demonstrate the poor reasoning skills of a ufologist, it's claims about evidence for aliens in ancient history. I already mentioned a few of the problems and assumptions that go into presuming a piece of ancient art shows alien spacecrafts, but often times the arguments these believers make are nothing more than arguments from ignorance, and I mean that in more than one way. I've heard ufologists comment many times about the strange things ancient peoples depicted in the skies, as if this lends credence to the UFO theory. The ancients thought the sun was dragged across the sky by chariots of the gods, but no one would be dumb enough to take that at face value and conclude that UFOs must have harnessed the sun and flown it around the earth in antiquity.
There's also a general lack of appreciation for history among these ancient aliens types. One shining example comes from the History Channel's Ancient Mysteries series, in an episode called "UFOs: The First Encounters." In the video, reference is made to two alleged UFO encounters had by Alexander the Great. These stories are presented as historically documented claims, and no cause for suspicion is given at all. But research reveals that the earliest accounts of this story are from a 1959 book by Frank Edwards and a 1966 article by Alberto Fenoglio. Neither one provides any sources, yet both are ufology-related publications. So much for the historical method on the ironically named History Channel.
It's undeniable that the ancients understood the world in a very different way from how we understand it now. Many ufologists don't seem willing to bother with consulting historians or utilizing critical thinking when it comes to ancient history, and the fact that people eat this stuff up is just plain sad. Modern accounts of UFO encounters at least have more of a basis for excluding certain phenomena. Most people today know what a shooting star is, we know about mirages, and a good number of us know about atmospheric events like the aurora borealis. Even if there are reliable accounts from history where people witnessed unexplainable things in the sky, we could not rule out these possibilities. Like I said, these were people who ascribed celestial bodies to the realm of the divine, and so even something like the sun was already seen as part of a craft of higher beings.
Of course, being the Religious Studies nerd that I am, the worst of it to me is the "UFOs in the bible" garbage. These claims typically revolve around passages like those from the Book of Ezekiel, where the narrator describes a prophetic vision. Ufologists presume that the text gives a literal report of a man seeing a UFO, but the interpretation of prophetic visions is a far, far more complicated subject, as any Jewish or Christian scholar will tell you. Part of the ambiguity to it is that even those who consider the vision to be "real" don't think it's really real. A vision is a spiritual experience, which many theists tend to understand as a sort of opening of the curtain of the physical world into an alternate dimension where the divine world is located. This behind-the-scenes view might be playing out only in the mind of the person having the vision, which would be consistent with the many claims of visions which were not witnessed, to some degree, by those standing by (as the New Testament tells of Paul's conversion). This is a pretty different claim from a UFO encounter, in which a person perceives a physical object with their natural senses, generally through no alleged intervention of the divine.
But there's another angle on prophetic visions that isn't considered. Take, for example, the Book of Revelation. Each of the visions had by John in the text relates to an event that takes place on earth, in the future or past, depending on a person's theology. So these visions are omens rather than literal visions, and if Revelation was meant to be a religio-political statement against Rome (as I believe it was), then there may never have been any visions at all - just a literary device used to communicate certain ideas. The "UFOs in the bible" claims are prime examples of taking scripture out of context to make very bad arguments from ignorance, and it's hard not to think there's a preconceived bias through which these ufologists have filtered the information.
I've only touched on a slim few of the claims made in Ancient Aliens and similar shows, but the formula doesn't change, I feel almost certain enough to guarantee. The most important thing to do with any claim, UFO related or not, is to check its sources, apply reason, and remember Occam's Razor. Devout ufologists sneer and jeer at skeptics, like we have committed to a predetermined conclusion of our own, and yet the evidence (or lack of it) speaks for itself. No argument that rests on misinformation, non-credible sources, or bald-faced unsourced assertions, is worth a grain of salt. Ancient aliens? I don't think so.