It’s time for school! The Astro101 series will cover some of the most important questions in astronomy. In today’s lesson, we’ll have: Why did people used to study astronomy? Why do they continue to study astronomy? What’s the deal with all this weird jargon? I discuss these questions and more in today’s Ask a Spaceman!
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So back in the day, and I'm talking really back in the day. This is past, oldie times. This is we're talking centuries. If you wanted an education, you didn't have a lot of options mostly because you were poor and starving but that's another discussion. The educational options, this tradition that I'm gonna talk about dates back to Europe before the first universities opened their doors a thousand years ago.
And remember, universities tend to have lifetimes longer than nations and actually the invention of the university is a pretty awesome and unique thing, but that that's not my podcast. This intellectual tradition that I'm gonna talk about, the seeds of it actually stretch back to Play Doh, which if you're going to claim intellectual pedigree, then there aren't a lot of better options. So when you wanted an education and you had the ability to have an education, you either went to study something practical like medicine or architecture through some sort of special school or collection of trainers or apprenticeships, or you trained in something called the liberal arts. If you showed up at university or or a proto university, you started with a curriculum called the Trivium, which is Latin for three ways or or the place where three ways meet. And, yes, there's a lot of Latin involved in this discussion because even though the Roman Empire died, it still lives on in our hearts.
The these three things that you studied, these three subjects were grammar, logic, and rhetoric. You studied the structure of language, the structure of thought, and then how to apply logic and reasoning and thought in the use of language to try to influence and convince people and make things happen. And after some amount of time, like a few years, you were were awarded with some sort of degree, like a bachelor's degree, and you were sent off into the world to do well, I'm I'm not exactly sure what you did with that. But if you stayed in the university and you had the time and money and skill to go further, you could enter another level of education. You could go for a master's degree in the liberal arts, And this master degree curriculum built on the trivium and refined it to more important and more detailed subjects, which are called the quadrivium, and you can guess that.
That means four ways. There were four subjects. So these are considered refinements and also more important. Like, the the education model of the oldie times was reversed. Like, nowadays, we start with the important stuff, the really, really critical stuff, and then we get to the more esoteric nuance details.
Back then, they started with, like, the broad brushes, the basics that were considered building blocks to the real knowledge, and the Quadrivium represented that real knowledge. And here we find four very interesting subjects that are building on grammar, logic, and rhetoric. We have arithmetic, geometry, music, and astronomy. From there, if you were so inclined, you could go on to study philosophy or theology or law and earn the equivalent of a doctorate. But if you stopped at these seven, the combination of the trivium and the quadrivium, these were called the seven liberal arts, which doesn't mean liberal the way we use it today, but in the sense of liberating.
That you needed to know these seven subjects in order to be a truly liberated person. It was these subjects, it was mastery over grammar, logic, rhetoric, arithmetic, geometry, music, and astronomy that made you a true, free thinking, independent, liberated person. Think about that for a second. How how how like, just just just that mind frame, which we still encapsulate today through our liberal arts colleges and universities. We believe that if you want to be a fully capable member of society, if you wanna participate in civic life, if you wanna make decisions that impact others, if you want to have a career, if you really want to think like we think people ought to think, you need to be liberated in your thoughts.
You need a certain structure of knowledge in order to have that for you, and astronomy was considered one of those essential parts. Studying astronomy was about studying motions and geometry, and it was a part of philosophy and theology. The the you're studying the structure of God's creation, etcetera, etcetera. But you're looking for patterns and rhythms and regularities in the world around you as represented by astronomy. You're looking for patterns in an otherwise chaotic universe.
This is a skill, the ability to discern and understand patterns in an otherwise chaotic world. It was considered essential for a truly liberated person. In the Western tradition, going back thousands of years, we see astronomy as essential for understanding essentially everything, for understanding harmonies, for understanding motion, for understanding patterns, for understanding influence and relationships. Astronomy here, the way I look at it as this part of the liberating arts, was as a protoscience, a way of looking at the universe in a very orderly, logical, rational way, a mathematical way. Astronomy was also kind of handy for navigation, which also helped make you made you liberated in a certain sense because now you could sail on the seas confidently.
But the main skill it imparted was an ability to see the universe in a way that you don't normally get to. It takes a mathematical thinking. It takes a logical thinking in order to view the universe in this way, and that way is provided by astronomy. So here we are. In my show these past few years, I get a lot of questions.
I love all of them. Thank you very much. Lots of potential directions to go in. You know, we can talk about astrophysical phenomena. We could talk about the latest news in astronomy.
We could dig into quantum physics. And this series that I'm starting with this episode isn't based on any single question except for a common one that I get, which is where do I start? Like, if you're if you're just entering the this show now, and you look at all the episodes with all the topics, you could start at episode one and go from there, or you could start to pick and choose just but but it seems random. It seems there's no relationship to it doesn't progress to anything. This isn't like a college course or a quadrivium.
And the real answer is of where do I start, where should you start in this podcast is I have no clue. There is no ultimate plan or purpose to the show except to provide complete knowledge of time and space. But I get it because topics float in and float out. You know, for a while, I'll talk about string theory, and then we'll go back to galaxies colliding. It can be hard to know where to go first, so here we are.
For you, if you're new to this series, this is a great place to start with this Astro one zero one series where I'm gonna cover some really solid basics in astronomy. And we'll talk about planets and solar systems and galaxies and the birth and death of stars and some basics of cosmology so that you have somewhere to go. And for you old timers, you know, the ones who've been hanging on all these years through all my rants and all through my Patreon bags and through all my jokes about cheese. Why should you listen to this series? Well, a, it never hurts to review the basics.
Trust me. B, you might just learn something. C, you're probably just listening for the sound of my voice while you're doing something else anyway, so I could just be describing cat grooming techniques for all that matters. Indeed, astronomy liberates you. Our ancestors realized that understanding astronomy helps you understand everything, scales, motion, place, and time and space.
So by reviewing astronomy, you are reviewing what it means to be a truly free person. You might hear some of the info that I'm gonna present in this series before, or it might be new, or it might be talked about in a new way. Either way, I'm going to enjoy it, and we can all agree that you don't want to hear me do a six part series on music or cat grooming techniques. Here's the fascinating thing about astronomy. It's an old profession.
The joke is that it's the world's second oldest profession done in some form by basically every single human culture to ever exist ever since there's been a human culture. And until recent times, this is the craziest part, we did it all without having the slightest clue what was going on. Astronomy means? I mean, it's just it's just so fun. Like like, now we understand things like planetary orbits and gravitation.
But back then, we just had points of light on the sky doing weird things, no clue what any of it meant, and trying to use it for useful purposes. What a mess. I mean, you gotta hand it to our ancestors. They're pretty smart folk. They're pretty smart.
Astronomy means the law of the stars and is different from astrology, which means to know the stars. And, yes, I have been introduced on radio shows, talks, talks, and even had posters advertising appearances calling me an astrologer, and, honestly, I don't blame people. The separation between astronomy and astrology is relatively recent. It really only happened in the mid eighteen hundreds. And I don't mean in terms of interchangeability of the words.
Like like, you go back a couple hundred years and astronomy and astrologer or astrology are essentially the exact same thing describing the exact same person. But there was a separation in the mid eighteen hundreds in terms of purpose. Now for millennia, the whole point of astronomy was to do one of two things, either agriculture, which is if you look at the world around you and how chaotic and messy and unpredictable it is, the motions of objects in the sky are one of the few obviously apparent cycles in nature, which in a chaotic world is a pretty nice thing to hang on to. Like, hey, When do we plant the spring harvest? Oh, it's when when this star appears above the horizon, and we can count on it every single year, and we don't need to stress out about it.
We know it's gonna be a good time to plant our harvest. And the other thing, the whole point of astronomy besides agriculture was for horoscopes. You know, predicting your future, telling you what you are like. And and this because since there was obviously some sort of connection between the motions of heavenly objects and what happens here on earth, then there is some sort of connection between the motions of heavenly objects and what happens here on earth. Like, okay.
If this star rising is directly connected to the exact right time to begin our spring planting, then is it really so much of a stretch to say maybe the position of SR has something to do with me personally? I'm not gonna blame ancient people for making that connection because the universe is so complex and so chaotic, and so unpredictable, and so dangerous, and the night sky is so radically different from all of that, and it is obviously connected to some regular patterns that we experience on the Earth, so maybe we can learn something by studying the stars. Maybe we can understand the law of the stars. Eventually, it did split with the rise of science, modern science, modern astronomy. It slowly we're talking over the course of couple of years.
I've told stories about Copernicus and Kepler, and there was astrology outgoing, you know, bleeding out of their eyeballs with astrology and horoscopes. But by the late seventeen hundreds, early '18 hundreds, you start to have a distinct profession of astronomer that is just concerned with mapping the stars for no other purpose whatsoever than to map the stars. And that doesn't really solidify into the mid eighteen hundreds. Today, astronomy is done by astronomers, also by astrophysicists. Now some people claim that these are synonyms.
I'm gonna push back on that. I myself consider myself an astrophysicist, more specifically a cosmologist. I studied the whole entire universe. Yes. I have worked with data.
Yes. I have worked with observations. Yes. I have made connections between theory and observations, but I'm not the one in there actually building the telescope, designing the telescope, doing the data analysis. Oh, I I do do data analysis sometimes.
Okay. The lines are blurry. I'll give you that. But if you walked up to an astronomer and called them an astrophysicist, they might be a little bit offended and vice versa. There's also an interesting split nowadays between the professional and the amateur astronomer.
It used to be if you were wealthy enough to have your own telescope, you qualified as an astronomer. Nowadays, astronomers tend to be, like, professors at universities, and then there are amateur astronomers that are just doing it for fun, but occasionally contribute to science. A lot of what I'm going to tell you in this episode would be perfectly understood by a professional astronomer slash astrologer from three thousand years ago because the basis of astronomy is what you see in the night sky, which is recording positions of objects and trying to predict what they'll be tomorrow night. And this strategy of, like, staring at the sky and trying to make predictions and measuring things didn't really change with the invention of the telescope four hundred years ago. Over the past few centuries, there has been a subtle shift from just recording what's happening and then moving on to trying to identify patterns so you can predict what's happening next.
And then there was another evolution, this was the scientific revolution, of trying to explain those patterns. But that's a very, very subtle shift. But still, even with quantum cosmology and supernovae and the Hubble Space Telescope, it all starts and ends with the sky. The sky is the laboratory of the astronomer. That is where all the action takes place.
Even with space telescopes, even with space probes, we're still launching them into the sky. The sky is what we care about. And so I want to spend the rest of the episode talking about some basics of the astronomical sky. And to understand the astronomical sky, I want you to imagine standing inside of a giant hollow sphere with points of light etched into the inner surface. And, by the way, welcome to the medieval cosmological model.
We are standing inside of a giant ball, and there's a bunch of points of light on the inside edge of that ball. This sphere rotates around us for some dang reason. We'll just add that to the list of things we'll figure out later. Hint, it's the rotation of the Earth, but we didn't know that back then. It just rotated for its own reasons.
It rises in the East, and it sets in the West. We call this the celestial sphere, and where you stand on the Earth determines what part of the celestial sphere you'll see directly above you and around you. Yes, we knew the Earth was round. We knew it was a globe for a very, very long time. We knew that the celestial sphere was just that, a sphere, and that you could see different parts of it by standing on different parts of the Earth.
There is a position directly above you. Wherever you're standing on the Earth, if you look directly up, that is called the zenith or zenith, and then the point directly below you is called the nadir. No matter where you are on the Earth, the celestial sphere appears to rotate around a fixed point. Now we know that these are the places where the north and south poles of the Earth stick into the celestial sphere. Like, if you go to the North Pole of the Earth and draw a laser pointer straight up, that is called the North Celestial Pole.
If you're in the Northern Hemisphere, you're especially lucky because there's a star near the celestial pole. We call it Polaris. It's that little star in the Little Dipper. In the South, you just have a lane cross that vaguely points in that direction, which makes makes navigation way harder in the Southern Hemisphere, at least it did. The further north you go on the Earth, the higher Polaris appears in the sky, which is a very handy way to determine your latitude.
Longitude, it took people a lot longer to figure out. So you've got your north celestial pole. There's the star Polaris, which happens to hang out nearby, and then you have the South celestial pole. And it appears like this entire sphere is rotating around that axis. And there's something called the celestial equator, which is like an equator, but for the sky.
It runs in a circle, like a belt halfway between the North celestial pole and the South celestial pole. So it's exactly like the earth's equator, but way up there in the celestial sphere, up in the sky. And just like on earth, you can find your position anywhere on Earth using two numbers. So with latitude and longitude, you can pinpoint anyone's position. So on the celestial sphere, we can pinpoint any position using two numbers, these two coordinates.
These two numbers are called declination and right ascension. And, of course, different cultures came up with different techniques, but this is the modern astronomy one, so we're gonna go with it. We need these two numbers. They're like latitude and longitude, but we call them declination and right ascension. Declination is the angle above or below the celestial equator, essentially how far north or south a particular object is.
Another way to view it is how far north or south you would have to travel in order to put that object directly above you. So, for example, Polaris has a declination of ninety degrees. It is ninety degrees north of the celestial equator, and if you were to travel ninety degrees north above our equator, as in put yourself in the North Pole, Polaris would be directly above you. For southern objects south of the celestial equator, there is we use negative degrees. So if there were a star near the south celestial pole, it would have a declination of negative 90 degrees.
Right ascension is a little more arbitrary and made up, just like the longitude on earth. Like, if you're trying to measure your East West position, that's different than measuring the North South. Like, North South is easy because we have our North Pole and our South Pole in the Equator. Like, things there's like a a system that just generally makes sense to everyone. But longitude, if you're trying to make a reference point for East West measurements or directions, that's a little more arbitrary because you have to pick somewhere to be zero.
And for various and sundry historical reasons, zero longitude ended up being the Greenwich Observatory in England. It could have been anywhere, but that's where it is. And just like longitude with right ascension, with this, like, left right, east west vibe on the sky, you need to pick a zero. And it could be anywhere, but you need to pick one. For astronomy, zero right ascension is where the sun is rising above the celestial equator on the vernal equinox.
So on the spring equinox, where that sun punches through the celestial equator, we're gonna call that zero right ascension. Why? Because the Greeks picked it a long time ago, and it kinda stuck. Instead of being measured in degrees, which would make a lot of sense, right ascension goes in a circle that's divided into twenty four hours. Each hour is divided into sixty minutes.
Each minute is divided into sixty seconds. Again, because reasons that make no sense and are totally arbitrary and made up. There is a slight technicality with this definition of right ascension, and by slight, I mean major, and that's the precession of the earth. The ancient people didn't really notice this, but slowly over the course of thousands of years, the Earth wobbles. Like, we're spinning, spinning, spinning, and our North Pole points in a particular direction in the sky, but that changes with time over the course of tens of thousands of years.
And so because this is changing, the right ascension of any object will change. Like, the sun is not gonna be in the same position every single spring. So in addition to the right ascension, you need to list what's called the epoch, which is the fancy and annoying astronomy term for a year. So if you know the year, the right ascension, and the declination, you can pinpoint any object on the sky any time of day. On that sky, we have interesting collections of stars, little patterns that we call constellations.
Constellations played a big role back in the day. These were a place where you could tell stories. These were the anchor for various horoscopes. Modern astronomy, about a hundred years ago, the International Astronomical Union decided on 88 constellations to cover the entire sky. No.
They did not ask cultures around the world for their input. So the 88 official, quote, unquote, constellations come from the Greek and Middle Eastern and European tradition of astronomy. Every culture in the world has their own set of constellations. These are the official ones. Why?
Because the International Astronomical Union said so. These constellations don't really serve a major purpose in modern day astronomy except to just divide up the sky. So you say, yeah. This is in the constellation Pegasus, so you know roughly where it is in the sky. There's there really isn't a lot of utility to constellation in modern professional astronomy nowadays.
You also have a special set of constellations called the zodiac, and lots of cultures have their own versions of the zodiac. If you look out, in addition to the stars, you also have these weird things called planets, which we'll talk about later. Planets have their own dance on the sky, but they all follow our particular line on the sky. Like, if you follow along with the path of the sun and then at night follow along with the path of the planets, they follow roughly the same line. Now we know is the plane of our solar system, but back then, people had no idea.
And so this the constellations that this line passes through are called the zodiac, the the constellations of the zodiac. I should mention that, basically, everybody knows what their birth sign is, which is, like, where the sun was setting or where the sun was at noon on the day of your birth or month of your birth. That's off, by the way, because of the precession of the Earth. The sun was actually nowhere near the sign of the zodiac that you think you are. It was actually, like it's it's actually in the, next one over by now because when everyone decided this, it was centuries ago, and centuries have happened, and the precession of the Earth has happened.
I just thought I'd mention that. Besides the stars on the sky, you'll also see the sun, which has its familiar twenty four hour cycle, a moon with roughly a four week cycle. There are phases of the moon, which back then we had no idea, but now we know it's because it's reflecting sunlight and why it's going through its different phases. We measure the size of objects on the sky using degrees. Yes.
I know right ascension is divided into hours, minutes, and seconds, but measurements are still made in degrees. Why? Because reason. Stop asking. You have 360 degrees, which makes an entire circle around the sky.
You can break, a one of the degrees down into 60 arc minutes and then each arc minute down into 60 arc seconds. To give you a sense of scale, the moon is 30 arc minutes across or about half a degree across. There is this moon illusion thing where when it's hanging out near the horizon, you think it's a lot bigger than it really is. That is a trick of your brain's perception. It's an optical illusion provided by your brain, but go out and measure it when it's near the horizon.
It looks super big, and then go out and measure it when it's right above your head. It'll be the exact same size. I guarantee it. There's a handy trick, and this pun is, horrible. Handy trick.
You you'll you'll see. You you can measure degrees using an outstretched hand. So for example and this is very rough, but it gives you a good ballpark. If you stretch out your arm and then hold up your pinky finger, your pinky finger is about one degree across. So it'd take 360 pinky fingers to make a complete circle around the sky.
If you hold out three fingers, that's about five degrees. If you hold out a fist from edge to edge, that's about 10 degrees. If you make the party horns, you know, where it's like the the pinky finger and your index finger, the distance between the tips of those fingers is about 15 degrees. And if you make the hang loose sign with your thumb and your pinky finger extended, the distance between those tips is about 25 degrees. And you can go measure this.
Go look for the Big Dipper. It's a very easy to spot constellation. And if you hold out your hang loose hand sign up to the Big Dipper, you'll see that the Big Dipper is about 25 degrees across. So moon is half a degree. It's about half a pinky finger.
Orion or sorry. Big Dipper is about 25 degrees or the size of a outstretched hang loose. There's some more astronomy jargon that I want to talk to you about. You may have heard of something called the sidereal time or the sidereal day. What we call a day is really the solar day.
It's the time it takes from the sun to go from noon and then noon again. One entire revolution of the Earth. But the Earth also moves in its orbit, so the time from noon to noon is a little longer than you might think. It's a little longer than the actual revolution of the Earth. You have to catch up to where the sun is in its new position because you've moved in your orbit.
So, like, imagine spinning in place while holding a flashlight, and then also trying to run-in a circle and then trying to illuminate something in the middle of that circle. What you'll find is as you spin, you'll flash your light on that object, bing bing bing at a regular rate. But as you walk around the circle every time you spin, you have to spin just a little bit more for your light to fall on the central object. Yes. You look ridiculous when you do this.
That's called a solar day or a day, and that's different than a sidereal day. A sidereal day is in reference to the fixed stars, how long it takes for the stars to return to their original position. And because the stars are so far away, the motion of the Earth in its orbit doesn't matter. A star will appear at the same position on the night sky at the exact same sidereal time every night, but not the same solar time every night. Yes, converting from solar time to sidereal time is a huge nightmare.
It's very messy and complicated, and yes, of course, astronomers use it because they just love messiness. The typical astronomer will use sidereal time rather than solar time because they're looking at the stars more often than they're looking at the sun. I know this episode is a lot of jargon, but welcome to astronomy. I'm not a huge fan of it either. I don't use 90% of it either because I'm more of an astrophysicist than an astronomer.
So I don't really care personally about sidereal time or the constellation positions. I'm looking at different stuff, but it's there. It's in astronomy, and you should know it. As for why all this nasty jargon exists, well, you can blame the fact that the vast majority of all this was developed before we had any idea of what we were talking about. So cut astronomers some slack.
They've been doing this for thousands of years, and when your traditions go back for thousands of years, some things get lost in modern translation. But before we go, perhaps the biggest what were they thinking piece of jargon slash definition has to do with brightness. It's kind of an important quantity. Certainly, you see brighter and dimmer things out there on the sky. And for most ancients, that was just fine.
You say, okay. That's the brighter one, and that's the dimmer one. What's the big diff? But the Greeks, for them, it wasn't this system of, you know, okay. Yeah.
There are brighter and dimmer ones. Who cares? This wasn't refined enough. So they developed a totally arbitrary and nonsensical system, kind of like Patreon, which makes very little sense except that you send money every month to keep this show going. Isn't that amazing?
Patreon.com/pmsutter. I'm not sure if you can thank the Greeks for that or not, but we can certainly try. So the Greeks created this system, and because a lot of modern astronomy definitions are based on the Greek and Middle Eastern and European traditions, we're stuck with it. The Greeks divided the stars into six categories, which they called magnitudes. Why?
Because the first magnitude stars are the brightest. They're the greatest magnitude. They are magnificent. The sixth magnitude stars are the dimmest. They are the least magnificent stars.
Roughly, first magnitude is twice as bright or was twice as bright as second magnitude. Second magnitude was twice as bright as third magnitude. Third, you get the point. But they couldn't measure this precisely. They were just using their eyeballs and guessing, like, okay, that's first set magnitude, that's brightest.
That's second magnitude, that's the second brightest category. Third, fourth, oh, wow. Look at these wimps. There's a bunch of six magnitude nobodies. In the eighteen hundreds, this was standardized, for what it's worth, so that a first magnitude star was, by definition, 100 times brighter than a sixth magnitude star.
So you still had these magnitudes, but now the lines became more clearly delineated, and it was set so that a first magnitude star was exactly 100 times brighter than a sixth magnitude star. But then we invented the telescope, and we started to observe stars that were dimmer than what the Greeks could see. So what's dimmer than a six magnitude star? What's less magnificent than a six magnitude star? A seventh magnitude or eighth magnitude or twentieth magnitude star.
But that's apparent magnitude. That's how a particular star looks like from the Earth, and stars can be bright because they're bright or because they're close, and stars can be dim because they're dim or because they're far away. And once you account for their distance, stars can have all sorts of different magnitudes. You might look at a star and think it's first magnitude super think it's super bright, but really it just happens to be close. And that if all the stars were the same distance away, it might drop down to, like, third or fourth magnitude.
So then astronomers introduced a measure of brightness based on a fixed distance called absolute magnitude, not apparent magnitude, absolute magnitude, and that fixed distance was chosen to be 10 parsecs. Yes. Astronomers use parsecs instead of light years. Parsecs were, invented by astronomers for various astronomical measurement reasons. Light year was invented by astronomers trying to communicate to the general public how far away stars really were, and so that's always been tainted by the association with the hoi polloi with the public, while its parsecs are truly inappropriately nerdy, so astronomers tend to use parsecs and not light years.
Once you adjust for distance, sometimes a magnitude can really drop. Like, oh, you think it's a bright star, but if you were actually, standardized distance away from it, it'd actually look really dim. Its absolute magnitude can be weaker than its apparent magnitude, but, also, a star can appear much brighter. There could be a six magnitude star that looks like a total WIMP, but if you were ten parsecs away, it would melt your face off. So what's brighter than first magnitude?
What's more magnificent than the first magnitude of stars? Zeroth magnitude. And what's brighter than that? Negative one magnitude. And what's really, like, a hundred times brighter than that?
Like, negative 10 magnitude. So when it comes to magnitude, big negative numbers means super bright, and big positive numbers means super dim. I can't keep going. We need a zebra break. Class dismissed.
Thank you so much for listening, and I do wanna give a big shout out. Oh, but go buy my book, How to Die in Space. It's a fun book. It's available on Amazon, so is the audiobook. Go to pmsutter.com/book to find out.
And please, please, please go to patreon.com/pmsudder. To learn how you can keep the show going, I'd like to thank my top Patreon contributors this month. They're Matthew k, Justin z, Justin g, Kevin o, Duncan m, Corey d, Barbara k, Nudadoo, Chris c, Robert m, Nate h, Andrew f, Chris l, Cameron l, Nalia, Aaron s, Tom b, Scott m, Billy t, and Rob h. It is their contributions plus the contributions of everyone else that keep this show going. Please send your questions to askaspaceman@gmail.com.
Hit me up on social media. I'm at paulmattsutter, or you can use the hashtag askaspaceman, and I will see you next time for more complete knowledge of time and space.