Tales from the Observatory

22 Mar

Old-school Cometary Theory: Above or Below the Moon?

5 Jan


How Do We Know if Something is “Above the Moon”?

Where do comets come from? Other than the sins of human beings rising every hour until the stench and horror turns into a comet (a reference to Andreas Celichius, The Theological Reminder of the New Comet, 1578).

So, Oort Cloud? Human sin? It could go either way.

Imagine that you’ve never seen a model of the Solar System. You have to construct it from what you see from the ground. You’re looking out over the horizon and you want to create a model of the universe.

You might come up some main areas from what you see; the stuff on Earth, terrestrial stuff, also sometimes referred to as ‘meteorological’. This isn’t just stuff on the ground. It’s anything that comes from our planet; clouds, rain, lightning, tornadoes, even meteors which only light up and become obvious when they enter our atmosphere, could be considered “meteorological”.

But you know there’s stuff above all the rain and the clouds. The Moon, for example, is often behind clouds, but conspicuously never in front of the clouds. The Sun is sometimes behind the moon, but never in front of the Moon.

You have the Sun and Moon areas, the things that move remarkably quickly in relation to you and dominate the sky and what you see. Then you have planets, and they move, but not like the Sun and Moon. They move slowly. Mercury moves the fastest, and if you’re living in pre-telescopic times, Saturn moves the slowest. But it does move, and its movement is obvious over a few weeks. Then there’s the stars. They don’t appear to move in relation to each other at all. Orion will forever be chasing a bull, followed by his dog, and squishing a bunny. So it’s logical from this perspective that there are only 2 or 3 regions of space: Earth, planet stuff, and the celestial sphere.

Why Won’t Comets Just Go Behind the Moon Already?

How do you prove something is somewhere beyond the moon? Well, an easy way would be if the Moon would just occult it. If the moon passed in front of Halley’s Comet, that would be a dead giveaway the comet was farther away than the moon. Alternatively, if the comet passed in front of the moon, then… it would have to be closer to us than the moon. Because that’s just how vision works.

But even before people knew that the slower planets were all farther away, we knew that Mercury and Venus were closer to us than the other planets (although which planet was closest to us, Mercury or Venus, was not figured out for some time). The placement of planets in relation to Earth, that is, the relative distances of planets, can be ascertained when planets transit, eclipse, or occult other planets. Just like when we see the Moon eclipsing the Sun, we say “hey, I guess the Moon is closer to us than the Sun”, when we see Venus pass in front of Mars, we say “hey, I guess Venus is closer to us than Mars.”

Comparison of Models

Note that regardless of whether it’s the Tychonic, Geocentric, or Heliocentric model, Mercury and Venus are always listed as the closest planets to Earth. Additionally Mars, Jupiter, and Saturn are correctly placed.

Transits and occultations were important for understanding the relative distances to planets, that is, which is closer, Venus or Mars? Mars or Saturn? For example, Kepler observed that Mars occulted Jupiter in 1591, and Maestlin observed Venus occult Mars in 1590.

Chinese astronomical records indicate that Mars occulted Saturn in 1027, Venus occulted Jupiter in 757, and a bunch of planets were occulted by the Moon a bunch of times. There’s a never ending record of the Moon passing in front of a bunch of things which we don’t have to get into, suffice it to say the Moon’s the closest to us and humans have known that for forever.

So now, building our Solar System by relative distance: If Venus occults Mars (in 1590) and Jupiter (in 757) and Mars occults Jupiter (in 1591) and Saturn (in 1027) then LSAT logic dictates that:

  1. Venus must be closer to us than Mars, Jupiter, and Saturn.
  2. Mars must be farther away than Venus but closer than Jupiter and Saturn.
  3. And either Jupiter or Saturn has to be the farthest away – ideally we’d get Jupiter to occult Saturn at some point. It happens, but rarely. I haven’t found a written record of it happening (if you find one, please send it my way with a source), but pretty much the oldest models of the Solar System we know of place Saturn farther out than Jupiter, so people knew. I don’t know if occultations were passed down orally or what, but they knew. I was unable to find a solar system model, even a really old one, even a really obscure one, with Jupiter farther out than Saturn. And I looked. Real hard. Took my whole Saturday.
  4. Since the moon has occulted a bunch of stuff at one point or another, humans knew the basic setup of the solar system well before the telescope, certainly before modern probes. It only takes a few eclipses and occultations to figure out which planets are the farthest from us, which are the closest, and that the moon is closer to us than everything else. Since no planet was (or ever will be) eclipsed by a star, it was also obvious very early on that the stars were much farther away than anything in the Solar System. And virtually every old-school model gets this general setup correct.

While I couldn’t find a specific historical example of Jupiter occulting Saturn, here are some examples of old-school models that placed Saturn past Jupiter:

Again, that old date of the Venus/Jupiter occultation, AD 757, that was way before the invention of the telescope. That was before heliocentrism really took off. But people still knew the relative setup of the planets because they were paying attention.

This is not, by any stretch a complete list of occultations that were written down all over the world. But isn’t it convenient that way before fancier methods came along astronomers were able to see which planets passed in front of each other and ascertain their relative distances in the Solar System?

Well… No. It’s not convenient, or luck, or coincidence. The Solar System is actually on a plane.

The problem is, comets aren’t generally on that plane. If they were, we could just wait until the Moon passes in front of them and it becomes super obvious that they live “above the Moon” but no. They don’t do that. The fact that comets aren’t on the ecliptic plane is important in the discussion on where comets are coming from.

Who Thought Comets Were Coming From Where?

Now, there were people that believed that comets came from Earth. Like wind, or lightning, comets blew in like a hurricane. Aristotle was one of them, true to his nature, he believed wrongly that comets were coming from the Earth itself. Now, he lived a long time ago so he didn’t have the Internet, but other Greeks before him, notably the Pythagoreans (according to Aristotle), believed that comets were planets, or perhaps just one planet, and lived where planets lived: Above the moon.

Other early sources of believing comets were in fact celestial was Apollonius of Myndus, a contemporary of Aristotle, and according to Apollonius (by way of Seneca), the even older Babylonians/Chaldeans thought that comets came from beyond the moon.  But according to Epigenes, the Babylonians thought they were atmospheric phenomena and came from Earth:

Going back to Aristotle, he believed that comets came from Earth; that they rose up from dry windy exhalations. He believed, basically, that they were atmospheric phenomenon – like weather. To prove this theory, Aristotle noted that comets are foreshadowed by wind and drought. That the wind and the drought proved that comets were atmospheric and came from Earth.

  •  “We may regard as a proof that their [comets] constitution is fiery the fact that their appearance in any number is a sign of coming wind and drought.”
  • “So when comets appear frequently and in considerable numbers, the years are, as we say, notoriously dry and windy.”

Aristotle, Meteorologica, H.D.P. Lee version (trans. 1951)

Now if you’re wondering, ‘wait, is there a correlation between comets and drought?’ No. No there’s not. This is one step away from Monty Python logic.

By the way, this isn’t even sort of the oddest “proof” that comets are actually from Earth. In John Edwards’ 1684 Cometomantia, John argues that yes, sure, astronomers say that comets are above the moon, but then why do they occur more frequently in Autumn? And also, smell bad? Answer me that learned astronomers!

Let’s Get Listy

If I go through every single person we have on record saying where comets come from, we’ll be here all day. So first up, an incomplete list of people who believed comets came from the Earth, Earth’s atmosphere, or “below the moon”:

  • Xenophanes of Colophon (570-475 BCE)
  • Aeschylus (525-456 BCE)
  • Heraclides of Pontus (390- 310 BCE)
  • Aristotle (384-322 BCE)
  • Metrodorus of Chios (300s BCE)
  • Theophrastus (371-287 BCE)
  • Strato of Lampsacus (335-269 BCE)
  • Epigenes (100s BCE)
  • Panaetius of Rhodes (185-110 BCE)
  • Posidonius (135-51 BCE)
  • Boethus (75-10 BCE)
  • Albert Magnus (1193-1280)
  • Georg von Peuerbach (1423-1461)
  • Nicolaus Copernicus (1473-1543)
  • Johannes Vogelin (1480s-1549)
  • Peter Apian (1495-1552)
  • Bartholomaeus Scultetus (1540-1614)
  • Scipione Chiaramonti (1565-1652)

People who believed comets were actually celestial objects living above the moon in true outer space:  

  • Babylonians (according to Apollonius) (circa 1700s BCE)
  • Pythagoreans (according to Aristotle) (500s BCE)
  • Anaxagoras (510-428 BCE)
  • Hippocrates of Chios (470-410 BCE)
  • Democritus (460-370 BCE)
  • Diogenes of Apollonia (400s BCE)
  • Zeno of Citium (334-262 BCE)
  • Apollonius of Myndos (300s BCE)
  • Artemidorus of Parium (it’s unclear)
  • Lucius Annaeus Seneca (4 BCE-65 CE)
  • Michael Maestlin (1550-1631)
  • Johannes Kepler (1571-1630)
  • Orazio Grassi (1583-1654)

And what about those people that just couldn’t choose a solid above or below the moon region? 

  • In the 1500s Jean Pena suggested that some comets exist beyond the moon. This was a pretty common comeback in the late 1500s.
  • Bernardino Telesio wrote on the comet of 1577. He wrote a book, On Comets and the Milky Way in which Telesio said that though comets originated from below the moon, some of them, such as the Great Comet of 1577, can rise high enough to become a part of the celestial region, beyond the moon.
  • Thomas Digges treated comets as celestial objects but then seems to switch in 1576 to treating comets as terrestrial objects in A Perfit Description of the Caelestiall Orbes. This was just sad, as the comet of 1577 basically proved comets were not from Earth (see page 33 of Donald Yeoman’s Comets).

And then there’s Galileo. What did Galileo think of comets? In 1619 Orazio Grassi wrote on the three comets of 1618 noting that since they essentially moved very slowly – slower than the moon – comets must be far away, and indeed exist beyond the moon.

This set Galileo off in a way that begs the question: Did Galileo think comets originated from Earth or from outer space?

The answer is, we don’t know for sure. We know he liked to argue with people. We know that with the help of a man named Mario Guiducci, Galileo took Grassi to task, arguing that comets could show no parallax because they might not even be real. They could actually be, like rainbows, an illusion.

Galileo went on to poke others who had made statements about comets, including Tycho Brahe who thought comets lived in the region between the Sun and Venus.

Kepler came to Brahe’s defense, and implied that Galileo was just jealous of Tycho Brahe, actually. But in his most famous work, Galileo stated that he did not care whether comets originated from above or below the moon.

The Comet of 1577

The Great Comet of 1577 was incredibly important in firmly moving comets from “could be meteorological” to “definitely coming from outer space”. Because the comet was pretty obviously farther away than the Moon.

So how do you figure out distance without a space probe and a really big measuring stick? With trigonometry. Of course. Which is largely the tool that old-school astronomers used to make measurements of the heavens.

Now we could talk about parallax but it really belongs in a video about the Cosmic Distance Ladder and that would take like, 70 hours. Suffice it to say, it’s not a coincidence that things closer to us look like they’re moving faster. People knew this. They knew clouds were closer to us than the Moon and that clouds moved faster than the Moon. From our vantage point on Earth (you know, the only vantage point) they knew the Moon moved faster in the night sky than planets and that it was closer to us than planets. No one ever said, ‘you know, the stars seem to not be moving in relation to each other at all, but I’ll bet they’re closer to us than the Moon’. That person doesn’t exist. I mean, maybe they existed – I just haven’t found them.

It’s not like the theory of comets originating from above the moon happened over night and was accepted because of one comet, but if one comet could be given the most credit, called the most influential, it is definitely the Great Comet of 1577. Similarly, the acceptance of comets as objects that originate well and truly from outer space cannot be credited to any single astronomer, but if one astronomer could be given the most credit, called the most influential on this topic, it’s Tycho Brahe.

Tycho showed that the comet had moved less in the night sky than the moon in relation to the background stars, that is, the comet showed less parallax. This required the use of a fine tuned instrument, but let’s first talk about what parallax is.

See people couldn’t say ‘oh this object has moved 4 miles today’ because they didn’t know how far away things were. All people could do is divide up the sky and say, ‘here’s my sphere, and it has 360 degrees, and each degree we’ll divide that further into 60 segments, we’ll say every degree has 60 minutes in it, and every minute has 60 seconds in it.

So all you can say at this point is, here’s how much this thing in the sky appears to have moved. That’s why you go back and you read these old books and it’s always like, ‘the comet moved 8 degrees and 3 minutes last night’ and never ‘8 km and 3 meters’. Because they’re really just saying what percentage of the sky the comet has moved across.

The problem with this is what if the object moves less than a degree? You need a quadrant big enough put the arc-minute notches onto. Actually if you were to get a circle and put all the degrees and all the minutes and all the seconds on it, you’d have 1,296,000 marks on your circle. In order to make those super accurate parallax measurements, I’d need to be able to put a whole lot of notches onto my circle/semicircle/quadrant/sextant.

So what’s a person to do?

Get a bigger quadrant. Which begs the question, how does one get a giant quadrant? Well, it helps to be propped up by the king. And that’s exactly what happened to Tycho Brahe. King Frederick the II of Denmark gave Tycho Brahe an island, a castle, and a whole lot of money to do his experiments with, making Tycho Brahe probably the highest paid astronomer of all time. And his instruments were the best, and the biggest. Only one other astronomer that I know of had a larger quadrant than Tycho Brahe; Ulug Beg, and he wasn’t just an astronomer for the king, he was the king.

Ah it’s good to be king!

Wait hang on, what’s parallax?

So let’s talk briefly about ‘parallax’. You know how when you’re driving down a road, the fence close to you flies by but the mountains in the distance don’t really appear to move all that much? Sure the mountains are bigger, but also, things closer to you appear to move more rapidly. [do the finger thing] My finger didn’t change size, my head didn’t move more, but it sure moves a lot less when it’s farther away.

The takeaway here is, when traveling past things that are far away, they appear to move slower than things that are close to us. A jet traveling hundreds of miles per hour in the distance appears to be moving slower than a jet traveling hundreds of miles an hour right over your head.

Now the Comet of 1577 was super bright. And also seen pretty much worldwide.

  • Japan
  • Czech Republic
  • Sweden
  • Belgium
  • Palestine
  • Peru
  • India
  • Turkey

Which is important, because what Tycho did (theoretically) was get another astronomer, 500 miles away to observe both the comet and the moon on the same night at the same time as he was observing them.

Ok, so let’s pretend the Earth is a sphere – go with me on a journey – and you’re looking at the moon, which is relatively close to us. There’s a guy over here, we’ll say he’s in Sweden, and a guy over here, we’ll say he’s in Prague, and they’re looking at the Moon and we’ll say it’s midnight. And guy over here’s looking at the moon going, yeah, it’s uh… kinda near the Pleiades and guy over here’s like it’s actually a little farther away from the Pleiades, and then they see the comet and they’re like, ‘yep, it’s in the same spot’. Well, that’s how you know, the comet is above the moon, beyond the moon, farther from Earth, than the moon.


This is a wild exaggeration and should only be used for illustrative purposes. However you can look at the moon from one location in Stellarium, and then choose another location roughly 500 miles away and see that yes, it does move in relation to the background stars.

Turns out, the moon was in a different location in the sky, because of course it was, but the comet wasn’t.


Again, an exaggeration. In reality, the comet would have appeared to move almost imperceptibly in relation to the background stars.

[Do the finger blink comparator again] Which means this was the moon [close] and this was the comet [far].

Your head is the Earth in this example.

Ok so, Tycho theoretically wrote all of this down , but I swear to god , it’s not translated.

Everything I have found is in Latin. Latin. Do I look like a person who learns Latin in their off time? Everything I’ve seen is a secondary source because nobody translated Tycho Brahe’s actual work on the 1577 comet?! This is Tycho Brahe! One of the most famous astronomers of all time – not Simon Stevin! – and I gotta read about him by some American? Why aren’t the Danish doing something about this? Who is the president of history?

Anyway, the Great Comet of 1577 was seen everywhere. It was seen in Japan, it was seen Europe, it was seen in India. The comet was big, bright, and far away.

For a list of texts and treatises on the Great Comet of 1577 check out C.D. Hellman’s 1944 book: The Comet of 1577. There were many.

So theoretically at this point, Tycho, and to be fair many other astronomers, realize that this comet had to be “above” the moon. It could not be atmospheric phenomena. Comets could not be created like tornadoes or wind or hurricanes – in short, they were not in fact coming from Earth.

People knew that the higher up something was, the more people could see it around the world, because it wouldn’t be below the horizon as quickly as something that was much closer, in this case the moon. In fact, about 70 years after the comet of 1577, a textbook writer in Paris, Pierre du Moulin, wrote that the fact that the comet was seen by so many in so many countries demonstrated its great height.

“Aristotle holds that comets are fiery exhalations: but the astronomers of this time have observed that a comet was above the moon. If that comet was a fiery exhalation, it would have always kept its tail behind it, in the manner of a torch, which when carried always keeps its flame behind it. And the fact that it was seen by so many in so many countries demonstrates its great height.”

And I think it’s important to note that this is not just one guy altering our view of astronomy, this is mostly just the most famous guy with the biggest annual income of any astronomer ever, altering our view of astronomy. Even before the comet of 1577 Girolamo Cardano (known primarily for his theories of probability and gambling) had stated that the comet of 1532 was above the Moon, precisely because it appeared to move slower than the Moon.

And it wasn’t an overnight change. Some astronomers still went down this road where they reasoned, ‘OK some comets live in outer space, but some still come from Earth’. It wasn’t an immediate discovery that kicked comets above the moon and well into outer space, but it’s not an overstatement to say that the Great Comet of 1577 was the nail in the coffin of an unfortunate spate of Aristotelian theories about comets being from Earth. After 1577 you pretty much had to explain why you still though comets were coming from Earth.

If I had to distill the not-so-linear-progression of old-school cometary thought, it would be:

  1. People knew the setup and relative distances of the Solar System because the Moon, Sun, and planets are on a plane and do eclipse each other from time to time.
  2. Comets are not on that plane and therefore people needed a different way of ascertaining distance.
  3. But people had noticed and knew that the farther away objects were, the slower they appeared to move in relation to the background stars.
  4. Armed with some pretty good logic, they then used a combination of parallax and large, finely tuned instruments to make comparatively accurate measurements of distances to “great” comets.

Thus ultimately placing comets beyond the moon, in at least the realm of planets, coming somewhere from true outer space.

I know I said last time to join me next time to talk about what are comets really? But I grossly underestimated how big of a historical argument it was that comets were above or below the moon, and how long it took for people to move past that.

So I guess instead, I’d file this one under Old-school Cometary Theory – you know, before people knew what comets even were. Join me next time to talk about New School Cometary Theory! And when I say New School I really mean, what are comets even, really?

Comets of DOOM

24 Jun


Full original text for Comets of DOOM video:

[I just saw Halley’s Comet she waved…]

Listen Brent, you didn’t see Halley’s Comet. Not in 2007. Be reasonable. It was Comet McNaught.

So I’m doing the Outer Solar System this month, but I’m working my way inward. Why am I starting with the Solar System? Cuz I been gone a while, and it’s easy.

And I’m working my way in because most people start at the Sun and then taper off by the time they hit Uranus and Neptune and the Kuiper Belt. Quite frankly, if anything needs to get the tired, sad, ‘I’m so over this topic’ treatment, it’s Mercury, not Neptune. So yeah.

What’s in the Outermost of the Outer Solar System?


Comets Are Unpredictable Because They Live Far Away and Visit Rarely

First of all, the Solar System is way bigger than most people imagine.

It’s bigger because we have this cloud of comets surrounding us, now called the ‘Oort Cloud’. That extends way out there.

The Oort Cloud almost definitely has more than a trillion comets in it, and it takes up an enormous amount of space. It starts at around 2000 Astronomical Units away and may stretch as far as 100,000 AU.

A lot of people still think of Pluto as being the end of the Solar System, but the Oort Cloud’s outer edge, that outer cometary edge, is about 2000 times farther away than Pluto is from us. Put that in perspective; if you lived in a tiny town, a town one mile wide by one mile wide in the middle of the continental US, and imagined that the Solar System we always hear about was in that town, everything up to and including Pluto, the Oort Cloud would be miles into the pacific ocean one way, the Atlantic Ocean the other way, in Canada, and Mexico.

My point is, it’s way out there. That’s the real end of the Solar System. The place where comets live.

Comets do come into the Inner Solar System from time to time, but it’s fairly rare. In fact, the setup of the Oort Cloud is what makes comets so… well… scary.

Comets, even today, aren’t super predictable. Even the ones that return, return with large margins of error, and often even look different from previous visitations – 1986 Comet Halley was no 1066 Comet Halley.

And it’s kind of hard to explain how upsetting it is to see something in the night sky that shouldn’t be there, because we’re all sort of used to it now. First of all, thanks to humans lighting up the night sky in perpetuity these days, very few Americans can even see the Milky Way from where they live. If you watch the night sky tonight, you’re likely to see far more planes than stars. We’re used to things moving up there.

But if you went back 100 years ago, even 50 years ago in most regions, you would see the same sky, every year, on the same day, forever.

And sure the sky moves, but it doesn’t really change – at least not on human timescales. Orion is always chasing Taurus and being followed by Canis Major. They move, but they never move in relation to each other. Orion will never show up in the night sky next to Scorpius. He can’t. He’s stuck chasing a bull and stepping on a bunny for a long time.

The Sky Is Remarkably Predictable – But Comets Aren’t

99% of what you see in the sky has a very regular pattern. Sure, planets move in relation to the background stars, but they move in predictable patterns. For example, Mars is really bright pretty much every two years. Every other year you’re going to get a bright red Mars in the night sky. And every other year, you’ll get a dim dumb Mars. Sure, it’s moving and changing way more than any given star, but it moves and changes in predictable ways.

Most of the night sky is like that. Now meteors and meteor showers can be shocking, but a meteor streaks across the sky for a second to a handful of seconds. And also, meteor shower intensity varies from year to year, for example, the Leonids peak about every 30 years so 2018 Leonids was no 2008 Leonids and 2008 Leonids was no 1833 Leonids, I’m just sayin. But they occur at roughly the same time every year (November) because meteor showers have to do with the position of the Earth in its orbit, and we orbit our star in a regular and predictable pattern.

Contrast this with comets. Comets will stay in the sky for days or weeks. They hang there like bright, ominous, tailed stars. They don’t really have a pattern. Mostly they just show up from time to time.

And that is shocking if you are used to seeing the night sky. Now I haven’t seen any bright comets. I’m up to PanSTARRS, Lovejoy, and Wirrtanen. None of them are stopping traffic.

But imagine you’re living a couple thousand years ago. You don’t what the Sun is, you don’t know what stars are, but you are aware of the heavens, how they look, and how they move. There’s no television, and you work outside a lot. And then a comet shows up. Even if comets are in the astronomical record of where you’re living, they are random, and surprising.

Cometary thought, at least, the cometary thought that’s been written down and preserved, often framed comets as omens.

And there is simply no way to talk about oldschool cometary theory without talking about superstition, astrology, religion, and doom.

So let’s talk about it.

I Don’t Give a Damn About My Bad Reputation

Pretty much the earliest undeniable records of comets come from China, because of course they do. Specifically, they come from the Silk Book from China, dated to around 170 BC.

This is not the oldest record of comets, but it is the oldest illustration with written descriptions that we have of comets. And those descriptions by the way, are all predictive. That is, they tell us what the result of the comet will be. Some of them are really unspecific, like 1 means war is coming, and generals will die. But number 2 signals a 5-day rebellion, and number 22 signals 3 small battles, and 7 large battles. That’s… really specific. Now, not all the comets are bad, but most of them are bad. You got war, death, disease, grief, war, famine, more war, good crops but internal war, battles in specific places, and oh yeah, more war. I’m sensing a pattern…

And the length of the comet tail was supposed to indicate the severity of the doom.

Now, these doomy predictions aside, the most complete and specific ancient records we have of comets all come from Chinese historical documents. Because they didn’t just say, ‘oh a comet appeared last year’, they wrote, here was this comet in this exact spot and this is how big it was and this how long it lasted and these are constellations it moved through and this was the direction it was traveling. That’s why historians can now say, ‘oh look at that, Halley’s comet was first seen in China and we’re pretty darn sure it was Halley’s Comet.

Also, for any book (and I’ve seen a few) that says Peter Apian was the first to point out that comet tails always point away from the Sun… no.

Around AD 635 the History of the Chin Dynasty was written and Li Chung-feng recorded that comet tails always point away from the Sun. This is the first known account of the antisolar nature of comet tails. Which is getting WAY too close to science.

So back to DOOOOOM.

Looking at that Silk Book from China, this was during a time when the Greeks and the Chinese didn’t have a working relationship, that we know of, so the idea that comets were bad, was arrived at most likely, independently.

Every society on the planet has done astronomy, and it turns out that comets were typically thought of as bad pretty much all over the world.

Many diverse bands of native Australians viewed comets as bad. For example, the Tanganekald of South Australia perceived comets as omens of sickness and death. The Kaurna of Adelaide appear to have associated comets with a pair of evil sisters, the Gundidjmara of Victoria saw comets as omens of death, and the Euahlayi of New South Wales saw comets possibly as terrestrial phenomenon that could take the rain out of clouds and cause drought, a not-terribly uncommon theory the world over. Comets causing drought was a weirdly common belief.

Comets as omens was pretty popular, but comets weren’t seen as bad always and everywhere. For example, in India, some groups of people such as the Banjara and Kolam thought of comets as predictive, sure, but not always a bad omen. Could be a good or bad omen. Could go either way. But other groups in India, notably the Gond people, saw comets as an actively good sign that the bad things humans had done was going to be swept away. So comets in this case, didn’t predict good things to come, but acted more like a redemptive or neutralizing force.

So comets aren’t bad always and everywhere to everyone, but more often than not in cultures very far away from each other, they were seen as omens, typically of bad things.

And for the Greeks, that was definitely the case.

Even in really old sources, comets are bad. For example, Homer, in the Illiad, wrote on the helmet of Achilles: “Like the red star, that from his flaming hair [comet = hairy star in Greek] shakes down diseases, pestilence and war…”

Aristotle had issues with comets too, but it’s really later sources that solidified the astrological consequences of comets. Let’s talk about Pliny the Elder. This guy decided to “give a description of everything that is known to exist on Earth.” Oh is that all? His work, Natural History, takes up 37 volumes and covers tens of thousands of topics. Basically, this guy wanted to be Encyclopedia Britannica. He wrote that comets had 10 types. We have… Pogonias, a comet with a beard hanging from its lower part, Xiphias; pointy like a dagger, Lampadias, appearing as a burning torch, you get it. Like the Silk Book, the varieties of comets are all based on how they appear in the sky.

And Pliny did dedicate too much space to the disasters that these comets foretold. And his Natural History was influential. Unfortunately, Pliny couldn’t read the signs of his own very avoidable death.

Pliny was killed by Mount Vesuvius, not because he lived in Pompeii but because he sailed over to see what all the hubbub was about. Either that or he had a heart attack on the way. It’s unclear, but it does seem that he was an unnecessary casualty of Vesuvius. Kids these days, and their Fear Of Missing Out.

Pliny didn’t help the cause of comets, but the cometary fear that later infested Europe can be traced back, not to Pliny, but to Claudius Ptolemy – kind of. Ptolemy lived from about 100-170 A.D. and was extremely influential on astronomy well into the 1500s. He’s best known for The Almagest, which was way more popular than anything Carl Sagan, Stephen Hawking, or Neil DeGrasse Tyson ever wrote. Basically, the dude was influential. Ptolemy also wrote The Tetrabiblos, in which he talked about comets and defended astrology’s relationship to them. Here’s where things get fuzzy. He was credited with writing The Centiloquium which were 100 specific rules predicting disasters associated with comets. Rules such as: “If the comet’s direction moves west to east, a foreign foe will invade the country” and “If the comet remains stationary, then the foe is domestic.” Here’s the rub; Ptolemy probably didn’t write The Centiloquium. Modern historians do not believe The Centiloquium was actually Ptolemy’s. In short it’s a fake. While The Centiloquium often appeared with The Tetrabiblos, the first time it appears is about 700 years after Ptolemy had died. Could it have been a hidden work for all those years? Yeah sure, but come on, if you were trying to sell an original Ptolemy to some king, with new and original texts on comets, maybe you’d make up a list of 100 astrological rules for comets and tack it onto the very famous Tetrabiblos too. A person’s gotta make money. In any case, “Ptolemy’s” astrological rules for comets became extremely influential in the Middle Ages. And guess what? Comets? They’re bad.

The Middle Ages

So now we get to the real crazy stuff.

There was this general period after the Romans but before 1608 that people generally look at as… kinda bad. There’s a lot of reasons the Middle Ages weren’t a time travelers dream destination, but one of them was that Europeans got really religious and real serious about tying pretty much everything back to God.

For example, the idea that the Star of Bethlehem was in fact, a comet, is not a new idea. Origen of Alexandria [185-254] suggested the Star of Bethlehem was a comet, but that it portended the ‘commencement of new dynasties’. The new star was not a sign of peace, but the establishment of Christian dynasty. In fact, you can find an unnerving number of after-the-fact illustrations of a comet hovering over the Siege of Jerusalem, which occurred in 70 AD. Often, the comet looks exactly like a sword. In this case, the comet wasn’t seen as good or peaceful, it was still an omen of doom – just someone else’s doom.

Religious philosophers (so like, everyone with an opinion at the time) went back and forth on whether comets were brought in by God or the devil or they were causes of sin or the consequence of sin, but one thing they seemed to agree on was that they weren’t good.

Bede the Venerable of Yarrow (673-735) “stated that comets portend changes of rule, pestilence, wars, winds, or heat.”

Thomas Aquinas (1225-1274) did nothing to assuage the considerable fear of comets but wrote that they were among the 15 signs preceding the Lord’s coming to judgment. Also Aquinas was extremely responsible for almost deifying Aristotle, and making his views the views of the church. So if you love Aristotle as much as first-year philosophy student, you can thank Thomas Aquinas for your misplaced adoration.

But you know, it was the 1200s. What do you expect? Well, let’s jump forward a bit.

Ah, here we go. 1493. The Nuremberg Chronicle:

“A great comet appeared in the month of January 1472. It was flame-colored and had a black tail. It proceeded westward but veered to the north. It was seen for eighty days, and before it vanished, another comet with a fiery tail appeared, proceeding eastward. Then followed an unprecedented drought; and later the plague broke out in a number of places, and there arose many dissensions, revolts and cruel wars.”

So comets bad.

Martin Luther (1483-1546) went even further and said that comets are harlot stars. He is quoted as saying: “The heathen write that the comet may arise from natural causes, but God creates not one that does not foretoken a sure calamity.” So we’re now up to, God is throwing comets at us. Great.

The “Enlightenment”

Even the “scientists” thought comets were doom-riddled:

Roger Bacon (1214-1294) observed a comet in 1264 appear in Cancer and move toward Mars, which he went on to proclaim “presaged discord and wars” (Yeoman).

Michael Mastlin believed the origin of comets was a mystery known only to God, but once created they were indeed celestial phenomena. However, he believed that the comet of 1577, though celestial, was still a portent of doom and proclaimed that it would bring peace, but a peace purchased only by a bloody victory (Yeoman).

Though Tycho Brahe studied the 1577 comet and made accurate (for the time) predictions about its distance to Earth, he also spent half of his treatise on the astrology of the comet. Basing his predictions on the position and color of the comet, Tycho concluded that it would bring death. A lot of death (Yeoman).

Kepler thought that when a comet was created a special spirit formed to guide it. The comet and spirit were created together and they dissipated together. He also took the ‘comet of doom’ farther than astrological significance which, of course, he had. He said that if Earth came into contact with the tail the atmosphere would become impure and a ton of people would die. In Kepler’s 1619 essay De Cometis Libelli Tres, he not only talked about the physical nature of comets, on which he said a bunch of wrong things, but also talked about their astrological significance which, of course, spelled doom, including: horror, long lasting rans, floods, universal epidemics, headaches, dissiness, catarrh (phlegm), and pestilence. So doom. Yeah. Doom. Kepler was on the Comet = DOOM train.

While comets may not explicitly appear in the Bible, in 1st Chronicles 21:16 we find: “And David lifted up his eyes, and saw the angel of the Lord stand between the earth and the heaven, having a drawn sword in his hand stretched out over Jerusalem.” (KJV). Later, the Jewish historian Flavius Josephus the destruction of Jerusalem in 70 AD and mentions “a star, resembling a sword stood over the city, and a comet which continued for a year.” (Schechner).

When God kicks Adam and Eve out of the Garden of Eden he places a “flaming sword” to guard their way back in. In the poem La Seconde Sepmaine, ou Enfance du Monde (1584) Du Bartas writes:

“Of our first Parents, our of Eden driven

(of repeal hopeless) by the hand of Heaven;

For the Almighty set before the door

Of the holy Park, a Seraphin that bore

A waving sword, whose body shined bright,

Like flaming Comet in the midst of night.”

In John Milton’s Paradis Lost (1667) he says:

The brandished Sword of God before them blazed,

Fierce as a Comet; which with torrid heat…”

Milton also likens comets to Satan in Paradise Lost when he says:

” Incensed with indignation, Satan stood
Unterrified, and like a comet burned,
That fires the length of Ophiuchus huge
In the arctic sky, and from his horrid hair
Shakes pestilence and war.”

You get the picture. Comets are bad.

Now, you might be thinking, ‘yeah sure but Maestlin and Brahe and Kepler… that was at the beginning of the scientific revolution. People needed time to let go of their astrological fear of comets. Surely, by the late 1600s cometary fears were mostly gone.’ And if that’s a thought you had, all I got is, ‘oh honey, people killed themselves in 1997 to get to Comet Hale-Bopp. Stop having faith in humanity.’

Maybe, maybe comets could have shaken their bad reputation with the advent of the scientific revolution. But then two great comets came in 1664 and 1665.

And so did the plague.

It’s at least possible the two comets of 1664 and 1665 and the subsequent chronology of the Black Plague and the Great London Fire had something to do with re-popularizing the comet of doom ideas. And they were popular.

In this case, that comets were bringers of doom, made sense. In 1664, for example, a comet appeared. In 1665, 1 in every 5 people in London died of the plague. Oh yeah, and then a year after that London basically burned down. Even Daniel Defoe of Lost in Space fame, I mean Swiss Family Robinson, I mean Robinson Crusoe, I mean The Martian, wrote about the comet moving across the sky, that it “portended a heavy judgment, slow but severe, terrible and frightful, as the plague.”

So comets couldn’t shake their bad reputation, and they couldn’t shake astrology. But… it’s important to note that the astrologers were still very wrong. For example, John Gadbury, astrologer, wrote a treatise called De cometis (they’re all called that) in 1665 in which he laid out the zodiac and said that if a comet arose in one sign, it would bring about certain events. For example, a comet arising in Aries denotes diseases of the head and eyes, a comet in Taurus portends sickness, A comet in Gemini portends grievous diseases for children, etc. Here’s the thing… There were comets in 1664 and 1665. And that year the plague hit London hard. From May to December 1665 almost 90,000 people died or about 1 in 5 Londoners. Of Gadbury’s 12 zodiac signs, only a few have no pestilence, death, or disease. But, comets arising in Virgo and Capricorn portended scandals and fornication respectively. Guess which zodiacal signs the two comets appeared in. Yeah. If Gadbury’s astrology had been correct, London should have been in the midst of the roaring 20s. Instead, everyone was losing their skin.

By the time we get to the next great comet, the comet of 1680, well, of the 62 known broadsides that were written on the comet of 1680, 15 years after the previous two comets of doom, almost all of them were bad. Only 2 of the 62 broadsides ring of anything other than astrological death and destruction. (Schechner)

Eventually the learned men of science let astrology go. Not as soon as they should have. But it went. But did they give up the doom?

Not a chance.

Even Edmond Halley, of Halley’s Comet fame, fell victim to the doom train. And this was the late 1600s, ok? The Dutch were figuring out early engines, a woman was co-running England, the Americans were burning witches… ok it wasn’t all progressive, and what did Edmond Halley think about comets? Well, on top of making some very nice observations, he also went in front of the Royal Society and… blamed them for causing the Biblical Noah’s Flood in 1694.


Two years after Halley’s proposed cometary deluge, William Whiston, in a book published in 1696 took Halley’s suggestion a step further and said that the comet caused a tidal break in Earth’s surface allowing subterranean waters to rise up and start the deluge, Noah’s Flood. He also predicted the end of the world via comet saying that a comet would come in and alter Earth’s orbit and fling it into the Sun. And when is this end of the world? 2255. Oh man, but that’s before humans get a chance to go back in time to save the whales. [Star Trek Voyage Home] We are so screwed.

And if you haven’t heard of Whiston, you have heard of his job. He replaced Isaac Newton as the Lucasian Professor of Mathematics at the University of Cambridge.


Ok, so it’s hard to get away from the comets of doom theories, but…

Are there any good comets?

One notable exception was Seneca [circa 4 BC – 65 AD], who said that Emperor Nero “redeemed comets of their bad reputation.” Before taking that at face value, bear in mind that Seneca had a super interesting life and may not have been serious. First, he was condemned to death by the Roman emperor Caligula but Caligula died, and Valeria Messalina, the empress of the next Roman emperor, Claudius, arranged for Seneca instead to simply be exiled to Corsica. Messalina was later murdered by Tiberius Narcissus a high ranking courtier with Claudius. So now Claudius needs a new wife. Narcissus suggested Claudius remarry his second wife, Aelia Paetina, but Claudius is like ‘I’m getting someone new’ and marries Agrippina the Younger (who was also his niece because this story was apparently written by George RR Martin). Agrippina gets in bed with her uncle/husband, makes a kid, emperor Nero perhaps you’ve heard of him and then she murders her husband, executes Narcissus, and installs her child as the next emperor. In hindsight, Narcissus shoulda probably not killed Messalina. Just sayin. Good ol hindsight.

What does this have to do with Seneca? Well, Agrippina brings Seneca back from banishment to teach her boy, the young Emperor Nero.

Guess who kills Seneca in the end? Yeah, it was Nero. Because the Romans were f-ing nuts.

Around AD 63 Seneca wrote Natural Questions in which he wrote about two comets that appeared during the reign of Nero Ceasar, which he wrote “saw the joyous reign of Nero” and “redeemed comets from their bad character”. To be fair, Seneca could have been trying to save his own life, or making a joke – sarcasm was invented before the Internet I promise – but less than two years later Nero ordered him to commit suicide anyway. And uh… he did.

So, one vote for comets being good from a man who was probably trying to avoid death by saying they were good. It’s not the best track record.

Comets of Doom meet Science of Doom

You might expect that the scariest comet of all time would occur in ancient Rome or the middle ages, but probably the best candidate for ‘scariest comet of doom’ was Halley’s Comet in 1910. Paradoxically, it was the advancement of the scientific method that lead to its ultimate position on the doom charts.

By 1910 scientists around the world generally understood that comets weren’t dangerous, but widespread public opinion hadn’t caught up. Also spectroscopy, a way to determine what elements or molecules a distant object possesses by essentially splitting light, was becoming the biggest tool in astronomy at the turn of the century, and scientists found out that good old Halley’s comet had toxic cyanogen gas in its tail. You know, like cyanide. So this combination of legitimate scientific eyebrow raising at the comet’s tail, and people’s long held suspicion of comets as bringers of doom meant that Halley 1910 was feared, almost worldwide.

Newspaper reports from China suggested that people were afraid they would be killed and that the comet might poison the water. In Croatia, France, and Austria-Hungary people sold their possessions in preparation for a short but happy rest of their lives. In Malta there was a successful press campaign to reassure the public that the comet wouldn’t harm them, but in Rome Pope Pius X had to denounce the hoarding of oxygen cylinders. And there were people that bought (and sold) anti-comet-tail pills. Similar stories come out of the United States, Russia, and England – which is understandable since King Edward VII did in fact die about a month before Halley reached naked eye visibility. (It couldn’t have been his almost constant smoking. It was the comet.)

Halley’s Comet 1910 was probably, hopefully, the last real vestige of belief in comets as harbingers of doom.

Join me next time for a tour of comet experts everywhere asking: But what even are comets, really?



Comets: A Chronological History of Observation, Science, Myth, and Folklore by Donald K. Yeomans (1991)

Comets, Popular Culture, and the Birth of Modern Cosmology by Sara Schechner (1999)

Personal Updates (August, 2015)

25 Aug

Holy carp! I haven’t written anything since February. LAME. In my defense, grad school is the worst. Seriously kids, don’t throw your life away on college (that’s what I’m going to tell my hypothetical children someday).

Mercifully, I only have ONE class left! And it’s an online class. And it’s not hard because I already took all the hard ones. Actually, I did that with my undergrad too – my last undergraduate class (I am not kidding here) was Intro to Computers, an 1100, freshman class, no one ever wanted to take that was basically ‘how to use Microsoft and make a Power Point’. I’m not sure how I pushed that to my very last semester, but I did.

As long as we’re confessing to things, I may as well throw in that I failed PE (a requirement at my school) 3 times. 4th time was the charm though.

This year I got to teach an undergraduate class, just to try it out and see if a PhD is worth it, and I have to be honest – it is not. Don’t get me wrong, I’d like to have a PhD, but getting one is a) ridiculously expensive, b) cost-prohibitive, and c) did I mention I don’t have the money? I’ve looked into scholarships, but there are not a lot of graduate scholarships out there, and I don’t really want to teach at a university. I’m not even sure it’s worth the time, let alone the money. Don’t get me wrong, I think education is important, but I think it’s going in a very different direction. MOOCs are getting more recognized, and huge amounts of research using citizen scientists are becoming more popular too. I think the day when you can teach and conduct real research outside of a university is just around the corner. So maybe universities should drop their prices is all I’m saying.

So in conclusion, my personal update is this: I’m almost done with grad school, I’m in a very ‘we don’t need no education’ mood, and I have no idea what I’m doing.

I’m pretty sure that’s how everyone feels after college. Right?






p.s. Oh yeah – the good news! I got made president of a small astronomy outreach NPO. That made my whole year.

Valentines Memes!

14 Feb Expansion of the Universe Valentine's Meme

So… Physics Today asked for some science-themed Valentines. I participated, but then of course… I came up with a bunch of astronomy-themed Valentines.

I felt like sharing! 🙂

IMBH Valentine's Meme

Mars Valentines Meme

Expansion of the Universe Valentine's Meme Supernova Valentines Meme

Pluto and Charon Barycenter

Black Hole Valentines Meme

Halley's Comet Valentine Meme  Comet Hale Bopp Valentines Meme

Understanding Black Holes (Part 2)

2 Nov

What’s the Difference Between Black Holes?

Specifically, Intermediate Mass Black Holes (IMBH) and Super Massive Black Holes (SMBH). Hope you enjoy it!


Links and things:

Understanding Black Holes (Part 1)

26 Oct

This is the first part of understanding the different types of black holes. An introduction to what black holes are and what makes them suck so hard.

Links and things:

Supermassive Black Hole by Muse
(Did you notice, Deecrowseer??? I totally used the correct song.)

Links and other info:
Dheeraj Pasham’s Website

Clips taken from:
Event Horizon, 1997, Paramount Pictures
Stargate SG-1, S2 E16, 1998, MGM Television
Star Trek, 2009, Spyglass Entertainment & Bad Robot Productions

Picture of Stellar Mass Black Hole

Stellar Evolution Diagram

GIF of spacetime

Black Hole Spacetime Comparison

3D Spacetime Illustration

Black Hole Regions

Awesome Nearby Star Systems

6 Jun

Nearby extrasolar planets are everywhere! Which is awesome sauce if you ask me.

How to Find Exoplanets (Transit Method)

17 May

How do astronomers find planets outside of the solar system? With the cunning use of spectroscopy.

Going Once…. Going Twice…

17 Apr

On Monday (ok, let’s be honest, it was really Tuesday) there was a full lunar eclipse.  I was at the observatory with hundreds of people (in a town so small you can drive from one end to the other in 10 minutes) for about 6 hours.  It was brutal.  Not because of the work, not because of the lateness, but because of the herds of people.

Oh sure, I may seem friendly on the surface, but after the first 56 people called it a ‘blood moon’ like the dead were going to rise from the grave, I started feeling a bit like Tim Minchin trying to explain how double-blind studies work to a girl named Storm.

It’s not that I have a problem with people – certainly not astronomy enthusiasts.  Generally, I have a problem with the media though, and in this case two things stuck out; calling it a “blood moon” as though that were special, and saying that it was a once in a lifetime event – both of which I later realized were problems of (mostly social) media.

So… the thing about lunar eclipses is that they are typically orange or red.  Also, they occur with great frequency, at least twice a year (although they are mostly partial so a full one is nice) and they are so, so, so not a once in a lifetime event.  Like even kind of.

Partial lunar eclipse 2011

Note the redness from this very partial lunar eclipse taken a few years ago.

Of course I was overjoyed to see so many people excited over the event.  Of course I was happy that lots of people came out. But there was a palpable deflation when people asked if this really was a once in a lifetime event, or if they’d ever get to see the ‘blood moon’ again like this and the answer was ‘of course’.  In fact, they could probably catch another one like this many times before they died.  Many people were clearly sad that this was in reality, not a once in a lifetime event.

That reality, that you will be able to see something only once is very strong in astronomy.  If you were alive in the 70’s-90’s, congratulations! Pluto got as close to us as it’s ever going to get in your lifetime.

Haley’s Comet, Comet Hale-Bopp, Comet Hyakutake, and Comet Pan-STARRS were all once in a lifetime events (unless you are Mark Twain).


You ain’t never going to see this again.

The Venus Transit was most definitely a once in a lifetime event (or twice in a lifetime if you were paying attention in 2004).

Venus Transit 2012

I almost cried that day. Not even kidding.

And there are plenty more where that came from.  If you were alive when Voyager 1 and 2 were launched, well, there was a planetary lineup that hadn’t happened since Jefferson was in office.

Sedna (my favorite planetary body EVER) will be at its perihelion (closest point) in 2076.  I’ll probably live that long!

Proxima Centauri is the closest star to us right now, but it hasn’t always been, and it won’t always be.  In 10,000 years, Barnard’s Star may be closer to us than Proxima Centauri, and in 30,000 some-odd years, Ross 248 will be closer to us than Proxima is now.

Movement of Close Stars

See that?  You are living the dream even as we speak.

And this is just astronomical phenomena.  We haven’t even talked about discoveries and human firsts.  There are so many astronomical discoveries that have occurred within your lifetime (even if you were born 12 months ago), I could make nothing but episodes on those, and I would never be finished.

Here are just a few that you have likely experienced:

  • Discovery of hundreds of new planetary moons in the solar system (over 20 were discovered in the year 2000 alone)
  • Discovery of extrasolar planets (1992)
  • Discovery of the first moon around an asteroid (1994)
  • Confirmation of the first brown dwarf (1995)
  • The discovery of multiple Plutoids; dwarf planets beyond Neptune (2004)
  • The Milky Way is shown to have a super massive black hole (2008)
  • The first probe enters interstellar space (2012)
  • First detection of an extrasolar asteroid (2013)

My point is, firsts and once-in-a-lifetime events are nice, but they’re not the most important part of astronomy.  They add to the pile of cool stuff, but they are not the pile itself.

No matter how common or how rare, it’s the experience, that counts.