Ancient Astronomy—From Stonehenge to the Great Pyramids: The Torch Podcast

An Interview with Professor Brad Schaefer, Ph.D.

On this episode of The Torch, we examine the pioneering efforts of ancient people, whose inquisitive nature led them to examine the skies, developing a deep understanding of the universe and our place in it, as well as creating the science of Astronomy along the way.

Here to discuss Ancient Astronomy and more is Professor Bradley Schaefer, Ph.D, Professor of Physics and Astronomy at Louisiana State University

The following transcript has been edited slightly for readability.

Ed Leon: There’s so much we can talk about in this course. Talk to me about some of the highlights that we’re going to understand about what these ancient civilizations were able to discover about the sky.

Brad Schaefer: There is an awful lot to understand, because the course is covering many millennia up until about 1600s, covering over the whole world. One of the highlights, the highest points of old astronomy, has got to be, what’s not too well know, it’s the Antikythera mechanism. This is that bronze fragment which was found on the seafloor near the island of Antikythera. It’s awesome.

By Tilemahos Efthimiadis from Athens, Greece – The Antikythera Mechanism Uploaded by Marcus Cyron, CC BY 2.0,

We’re actually incredibly lucky that sponge divers randomly found it in a shipwreck on the bottom of the ocean. What it is, it’s a bronze geared mechanism. It’s an analog computer. A person turns a crank, pointers move around, and it answers all sorts of astronomy questions.

Ed Leon: Are you serious? Do we know how to use it? Have we figured out how to use it?

Brad Schaefer: Replicas have been made. Yes, we actually do know how to use it. Not all of the Antikythera mechanism has been found, because it was lying in fragments on the bottom of the ocean. A Greek astronomer friend of mine told me that a few days ago, the current expedition which is looking for more fragments, actually did find a large fragment of the Antikythera mechanism. Maybe this might be the lost planetary set of gears deep in the interior. We don’t know.

Ed Leon: How did these ancient astronomers learn about the sky? Was it purely sky-watching? Did they spend days and years doing that? Talk about that.

Brad Schaefer: It depends on whether you’re one of the high researchers, the Hipparchus, the Ptolemy. They would have to have learned a lot of what had already been known from reading books. Most of ancient astronomy is people going off and doing calendars, and time-keeping, and navigation, and things like that. That was the work-a-day thing of ancient astronomers. For those sorts of things, a lot of what you learn is just by looking up. If you’re wanting to appreciate what the ancient astronomers could and did do, maybe one of the best ways, is just to go on outside and look up.

Ed Leon: Look up, and experience the same thing they experienced. By the way, is it the same? We go out. We’re going to see the same sky that they saw in ancient Greece?

Brad Shaefer: Oh well, the planets will be in a different location, but yes. Although, with city light pollution …

Ed Leon: Yeah, I was going to say, is the ambient light … Did they get a better picture, basically because of the ambient light and pollution that in the …

Brad Shaefer: If you go out to a dark site and just, with no moon, look up on a clear night, it’s awesome. The stars are all over the place. You can see your position in the universe.

Ed Leon: The skywatchers in different parts of the world …  Because the Maya had their own theories, and Greece, and some of the other parts of the world, Chinese astronomers. Did they discover the same things at roughly the same time, or did everybody bring their own insight into it?

Brad Schaefer: Every culture always had specifics to their own culture, which were special for themselves.

Ed Leon: Talk about some of the differences.

Brad Shaefer: Largely, the cultures had one or two tracks which the cultures followed along. For example, if you look in the western astronomy, typified by the Greeks and Mesopotamians, and you compare it to the completely independent Chinese astronomy, they’re kind of going … Well, discoveries aren’t made at the same time, but they’re following the same basic trajectory. Many of the cultures outside of Eurasia also were following very similar trajectories.

image of stonehenge - a famous advancement for ancient astronomy
Stonehenge’s ring of standing stones are set within earthworks in the middle of the most dense complex of Neolithic and Bronze Age monuments in England, including several hundred burial mounds.

Ed Leon: You start the course at Stonehenge. Why?

Brad Schaefer: Because Stonehenge is the most famous. It’s beautiful. If you’ve ever been there … Actually, you can’t get inside Stonehenge anymore. It’s horrible. Although I have been able to get inside, because I had got special permission. I have gone around and touched the stones. No sparks flew when I touched the stones. They’re not TV shows, where you see the sparks show, and people, “Hmm,” but that didn’t happen. Still, it’s wonderful. You can see right down the avenue. That’s where the sunrise happens, and it really does happen. There are good ways of getting together. Stonehenge is, by far and away, the most famous artifact of ancient astronomy. It typifies the idea that you have to be able to go off and get a calendar. That’s what’s going on.

Ed Leon: Explain it. What is Stonehenge at the end of the day?

Brad Shaefer:  The basic picture of Stonehenge is well known.

Ed Leon: But the functionality? Explain it, the functionality?

Brad Schaefer: If you stand at the center of the circle, look down the main avenue over the heel stone, fairly far away, you can see mid-summer sunrise. It’s a calendar marker, in some ways. Actually, that’s the popular idea. We’re going to be spending a reasonable amount of time pointing out that that’s not actually right. It turns out, if you have an alignment towards mid-summer sunrise, well, that same line also points backwards, in the modern sense, to mid-winter sunset. It’s a little bit ambiguous which one it is. It turns out it’s probably mid-winter sunset. The modern neo-druids who go there in their white robes and fake beards, those people got it wrong. It probably actually is mid-winter sunset. That’s new archaeological research that’s been coming out, new results on this, where we actually got that part of the basic Stonehenge picture wrong.

Ed Leon:  Let’s say I’m in ancient Greece, and I’m an astronomer. Take me through what they would have done. Take me through a Greek discovery that they figured out.

Brad Schaefer: It depends on whether you’re one of the work-a-day astronomers, in which case, you might have a thing called a parapegma, where you keep moving pegs around and you’re basically trying to predict the position of the planets for astrology purposes, or you’re trying to predict the upcoming weather, or you’re trying to predict the various festivals that are tied to the calendar. At another level, one of the heights of Greek astronomy was when Hipparchus went off and discovered precession.

Ed Leon: What is that?

Brad Schaefer: Precession is the motion of the stars in the sky. It’s an additional motion that we don’t see.  The North Pole of the earth kind of rotates around. It takes a long time, 26,000 years. It’s a slow effect. Hipparchus discovered this. 

Ed Leon: How did he discover this?

Brad Shaefer: He was always cocksure, and he was a grouchy old guy. He was always pointing out people’s errors, but he was very precise. It’s this precision which allowed him to make it. He was comparing his observations with older observations and noticed that the stars were moving with respect to the equinoxes. There’s a bit more of a story here. We’re going to go talking about this, of course. It’s kind of a weird thing. Okay, Hipparchus discovered precession. Within the Greek mindset that the earth is set, what it’s doing is, someone or something is taking the outer sphere of the stars and is taking this biggest thing in their known universe, and is rotating it.

Ed Leon: Wobbling it or whatever, right?

Brad Shaefer: The only thing that could do this is some sort of an uber god. What happened is, right after Hipparchus’ death, just a little bit down the coast, a whole new mystery religion arose. It’s called Mithraism. There’s a reasonable, but not proven, claim. It’s a reasonable claim, that the whole origin of the central mystery of Mithraism is Hipparchus’ precession. After all, the logic is there. Hipparchus discovered that somebody, something, is taking the whole universe and turning it. The only thing that’s that big is a god. It has to be a new god. They developed this whole religion, called Mithraism. The whole religion of Mithraism expanded quite a lot throughout the Roman Empire. Actually many of the Roman emperors were Mithraic initiates. For about a century and a half, a couple centuries, you had the Roman Empire dominated by this Mithraism’s and things. You can just imagine poor Hipparchus sitting there, “Holy Cow, my discovery made into a religion. What does that make me?”

Ed Leon: Talk to me about the Chinese approach, their constellations.  By the way, did everybody see constellations?

All cultures have constellations. Every last one of them. It’s probably because you have the universal of: humans are pattern recognition machines.

Brad Schaefer: The Chinese constellations were … They had, it depends on exactly how you count, but 270 constellations. All of their constellations had to be a lot smaller and there were a lot of weird things floating around. All cultures have constellations. Every last one of them. It’s probably because you have the universal of – humans are pattern recognition machines.

Ed Leon: Pattern recognition, right. Absolutely.

Brad Shaefer: The stars are universal. You make a pattern, and you want to tell stories. Every culture, everywhere, put constellations up in the sky. What the Chinese did, one of the things the Chinese did, was they had their philosophy put on their shirtsleeve, up in the sky. Their philosophy was that you had the emperor, and he was represented by, effectively, what the North Pole is. You have all of the stars turning around the emperor. The emperor, at the North Pole, is never moving. Everyone was going around him. It never set. Hence, in some sense, immortal. Their constellation pictures had the emperor and the imperial palace up in the region near the North Pole where the stars never set. As you got further and further away from the North Pole, as you got further and further away from the emperor, you got farther and farther out in the empire, and you started going to lower and lower rank.

Down at the very southern end of the sky, that’s where you have the peasants. Up in the northern side is where you have the great generals and the high official. In the middle, you had perfectly ordinary things. Down in the far south, that’s where you put the constellations for the dogs. There are three of them scattered around the southern edge.

Here’s a weird kind of one. Just south of what we now call Orion, there is a constellation. Again, this is getting far away from the emperor, so we’re going to lower and lower status. There’s a constellation there, which is basically an outhouse. It even has a vanity, a privacy screen. There’s another constellation, the privacy screen, right next to it so people can’t see in. Characteristically, just below the outhouse, is a constellation called “shi.”

Ed Leon: Makes sense to me.

Brad Shaefer: I don’t have to tell you what it really is.

Ed Leon: I put two and two together.

Brad Shaefer: Exactly. I don’t think that’s the real origin of the expletive.

Ed Leon: That’s funny. You’d mentioned all the cultures. The Islamic culture, also, had astronomers. The Golden Age of Islam also contributed to it. Talk a little bit about that.

Brad Schaefer:    They had a variety of things. They were going off and trying to impart, meet the needs, of their new Islamic religion. The Islamic astronomers spent a lot of time on things that support the Five Pillars of Islam, which are the five requirements. One of the requirements is a daily prayer, but the daily prayer times are mandated effectively by the position of the sun, the altitude of the sun in the sky. They had to come up with commonly used devices, and so they were using astrolabes. They developed and used them, fair enough. You also had to know, for the pillar of prayer, you also had to know what direction to face towards Mecca. How do you, you’re off in the middle of the dessert, how do you know what direction to face? Again, the astrolabe could help solve that. They also worked a lot on geography.

One of the other Pillars of Islam is that you had to have this pilgrimage to Mecca, and you had to know which days. That meant you had to know what day of the year to do particular rituals. Also, one of the Pillars was, you had to have fasting during Ramadan, so you had to know when Ramadan was. That was all that the Islamic lunar calendar depending entirely on visibility.

Ed Leon: They were able to answer those questions?

Brad Shaefer: Yes, so they spent a lot of time on that. Most of the Islamic astronomers of the era were aimed at those questions. For example, Omar Khayyam. People in the west, my sister, “He’s a poet.” Okay, that’s what you should say, but you go into Islamic communities, Omar Khayyam is remembered as being an astronomer. He’s the one who, basically, invented the calendar now used in Persia, even now used in Persia. He’s an astronomer, not a poet.

By Jean Naze (1539–1581) – Marie-Lan Nguyen (User:Jastrow), 2008-12-26, CC BY 2.5,

Ed Leon: You mentioned the astrolabe, what technology played into this? Did every culture come up with their own technology? Was it only observational and marking down the sky. What did they use to come up with these incredible calculations?

Brad Schaefer: The basic astrolabe is just a flat bronze thing with a couple different plates and little pointers that move around on it. In principle, the basic idea for the astrolabe goes back to, certainly to Ptolemy, and probably Hipparchus. The basic idea of the astrolabe, the Arabs had taken from the Greeks. The making, and the manifestation of the astrolabe, that’s all Arab. They did a wonderful job. It’s a very functional … Actually don’t have one here. I’ve got one in the other room. I could show you. It’s kind of evocative. It’s a beautiful little bronze instrument. You move things around. You hold it up. There’s all sorts of fine etch-lines.

Ed Leon: But someone invented that. Are all these, the names of these inventors and astronomers, are they all lost to time?

Brad Schaefer: Many of them are. The particular inventor of the astrolabe, push come to shove, I’ve already given the name. At least the concepts, and maybe the ideal, came from Ptolemy or probably Hipparchus. That wasn’t the realization that led to these beautiful bronze instruments. We don’t know particular names of the instrument makers. It was a bit of a slow progression, in the usual way, to get those up and working in a functional form.

Ed Leon: At what point did we all figure out, or someone figure out, that the world was round and not flat?

Brad Shaefer: Aha, right. Most cultures around the world, that were not in touch with the Greek or Chinese, viewed the world as being flat. They didn’t think about it much, but they viewed the world as being flat with a sky-dome over it. The gods lived up in the sky-dome. They believed that, up until the time the European travelers came and imposed a different idea.

However, within most of Eurasia, the realization that the world was not flat came, oh, I don’t know, 300 or 400 BC. The world converted quickly over. The Chinese, independently, came up with the same thing. Largely, all of Eurasia, by 200 BC or some such number, everyone knew the world was round. They were measuring the sizes, both in China and in Greece, and elsewhere, and in Egypt. They were actually measuring the size of the earth. They knew the earth was round. That also explained the eclipses for them.

Ed Leon: Doing a course like this, what blows you away? What blows your mind sometimes when you think back on what these ancient astronomers were able to achieve and figure out?

Brad Schaefer: There were a lot of things that they did with remarkable precision. They found the orbital periods of the planets to fractions of a part per million.

Ed Leon: Yeah, it’s crazy.

Brad Schaefer:    Here’s another one. This is a hard one for me. The Great Pyramid, holy cow. For the Great Pyramid, it’s aligned. It’s got orthogonal sides. Those sides are aligned north-south, and others east-west, to an accuracy of 1/20th of a degree. It’s a tenth the size of the full moon. How can you do that? I still don’t know. There are a variety of ideas. It’s incredible that they could have possibly done that.  All of their pyramids are oriented that way.  There’s actually a good reason for why their pyramids are oriented that way. It’s simply because … Again, it’s the philosophy of the ages. It’s how the ancient Egyptians connected their directional symbolism up to the sky. For them, rather logically, the direction towards the east, with the sunrise, that’s the direction of birth. The direction west is where the sun goes away, sets. That’s the direction of death. The cities are on the east side of the Nile. Their cemeteries and their pyramids are put on the west side of the Nile. To the north, that’s where you had, again, those stars that never set. The analogy would be, if the stars never set, they’re immortal. That’s where heaven was. That’s where the Pharaoh’s soul has to go. It’s part of this directional symbolism for why they wanted to align the pyramids north-south and east-west to high accuracy.

Ed Leon: It’s back to the story-telling. That’s what makes it such a fascinating course. The course is called “The Remarkable Science of Ancient Astronomy.” We’re so glad to have had Brad Schaefer, professor of physics and astronomy at Louisiana State with us today. Thanks so much. Looking forward to it.

Brad Schaeffer: Should be fun

From the Lecture Series The Remarkable Science of Ancient Astronomy
Taught by Professor Bradley Schaefer, Ph.D.  
By No machine-readable author provided. Marsyas assumed (based on copyright claims). [GFDL (, CC-BY-SA-3.0 ( or CC BY 2.5 (], via Wikimedia Commons