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hello, and welcome to crash course astronomy!i’m your host, phil plait, and i’ll be taking you on a guided tour of the entireuniverse. you might want to pack a lunch. over the course of this series we’ll exploreplanets, stars, black holes, galaxies, subatomic particles, and even the eventual fate of theuniverse itself. but before we step into space, let’s takea step back. i wanna talk to you about science.

crash diets wiki, there are lots of definitions of science,but i’ll say that it’s a body of knowledge, and a method of how we learned that knowledge. science tells us that stuff we know may notbe perfectly known; it may be partly or entirely wrong. we need to watch the universe, seehow it behaves, make guesses about why it’s

doing what it’s doing, and then try to thinkof ways to support or disprove those ideas. that last part is important. science mustbe, above all else, honest if we really want to get to the bottom of things. understanding that our understanding mightbe wrong is essential, and trying to figure out the ways we may be mistaken is the onlyway that science can help us find our way to the truth, or at least the nearest approximationto it. science learns. we meander a bit as we useit, but in the long run we get ever closer to understanding reality, and that is thestrength of science. and it’s all around us! whether you know it or not, you’re soaking in science.

you’re a primate. you have mass. mitochondria in your cells are generating energy. presumably,you’re breathing oxygen. but astronomy is different. it’s still science, ofcourse, but astronomy puts you in your place. because of astronomy, i know we’re standingon a sphere of mostly molten rock and metal 13,000 kilometers across, with a fuzzy atmosphereabout 100 km high, surrounded by a magnetic field that protects us from the onslaughtof subatomic particles from the sun 150 million km away, which is also flooding space withlight that reaches across space, to illuminate the planets, asteroids, dust, and comets,racing out past the kuiper belt, through the oort cloud, into interstellar space, pastthe nearest stars, which orbit along with

gas clouds and dust lanes in a gigantic spiralgalaxy we call the milky way that has a supermassive black hole in its center, and is surroundedby 150 globular clusters and a halo of dark matter and dwarf galaxies, some of which it’seating, all of which can be seen by other galaxies in our local group like andromedaand triangulum, and our group is on the outskirts of the virgo galaxy cluster, which is partof the virgo supercluster, which is just one of many other gigantic structures that stretchmost of the way across the visible universe, which is 90-billion light years across andexpanding every day, even faster today than yesterday due to mysterious dark energy, andeven all that might be part of an infinitely larger multiverse that extends forever bothin time and space.

see? astronomy puts you in your place. but what exactly is astronomy? this isn’tnecessarily an obvious thing to ask. when i was a kid, it was easy: astronomy is thestudy of things in the sky. the sun, moon, stars, galaxies, and stuff like that. butit’s not so easy to pigeonhole these days. take, for example, mars. when i haul my ‘scopeout to the end of my driveway and look at mars, that’s astronomy, right? of course!but what about the rovers there? those machines aren’t doing astronomy, surely. they’redoing chemistry, geology, hydrology, petrology… everything but astronomy! so nowadays, what’s astronomy? i’d sayit’s still studying stuff in the sky, but

it’s branched out quite a bit from there.borders between it and other fields of science are fuzzy… a theme i’ll be hitting onseveral times over this series. humans might like firm, delineated boundaries between things,but nature isn’t so picky. and that brings us to our first edition of“focus on…” this week’s topic: astronomers! who arewe? what do we do? i used to look through telescopes for a living,or at least study the data that came from detectors strapped onto them. but now i talkand write (and make videos) about astronomy, and relegate my viewing to my personal backyardtelescope. but i still consider myself an astronomer, so that should give you an idea thatthere’s a lot of wiggle room in the profession.

in fact, when i worked on hubble space telescope,i was actually hired as... a programmer! i coded in the language used by the folkshelping to build and calibrate a camera that was due to launch into space and be installedonto hubble by an astronaut. once the data from that camera are taken andanalyzed, you have to know what to do with them. do the observations fit the physicalmodel of how stars blow up, or how galaxies form, or the way gas flows through space?well, you better know your math and physics, because that’s how we test our hypotheses.and someone who does that is generally called an astrophysicist. of course, those telescopes and detectorsdon’t create themselves. we need engineers

to design and build them and technicians touse them. most astronomers don’t actually use thetelescopes themselves anymore; someone who’s trained in their specific use does that forthem. some of those instruments go into space, andsome go to other worlds, like the moon and mars. we need astronomers and engineers andsoftware programmers who can build those, too. and then, at the end of all this, we needpeople to tell you all about it. teachers, professors, writers, video makers, even artists. so i’ll tell you what: if you have an interestin the universe, if you love to look up at the stars, if you crave to understand what’sgoing on literally over your head, then who

am i to say you’re not an astronomer? however you define astronomy, humans havebeen looking up at the sky for as long as we’ve been humans.certainly ancient people noticed the big glowy ball in the sky, and how it lit everythingup while it was up, and how it got dark when it was gone. the other, fainter glowy thingtried, but wasn’t quite as good as lighting up the night. they probably took that sortof thing pretty seriously. they probably also noticed that when certain stars appeared inthe sky, the weather started getting warmer and the days longer, and when other starswere seen, the weather would get colder and daytime shorten.

and when humans settled down, discovered agriculture,and started farming, noticing those patterns in the sky would have had an even greaterimpact. it told them when to plant seeds, and when to harvest. the cycles in the sky became pretty important.so important that it wasn’t hard to imagine gods up there, looking down on us weak andridiculous humans, interfering with our lives. surely if the stars tell us when to plant,and control the weather, seasons, and the length of the day, they control our livestoo… and astrology was born. astrology literally means “study of thestars”; as a word it’s been used before science became a formal method of studyingnature. it irks me a bit, since it got the

good name, and now we’re stuck with “astronomy,”which means “law or culture of the stars." that’s not really what we do! but what theheck. words change meaning over time, and now it’s pretty well understood that astronomyis science, and astrology… isn’t. millennia ago, astrology was as close to scienceas you got. it had some of the flavors of science: astrologers observed the skies, madepredictions about how it would affect people, and then those people would provide evidencefor it by swearing up and down it worked. the thing is, it really didn’t; the faultof astrology lies in ourselves and not our stars. people tend to remember the hits andforget the misses when predictions are made, which is why they sometimes sit in casinospumping nickels into machines that are in

proven to be nothing more than a method forreducing the number of nickels you have. but astrology led to people to really studythe sky, and find the patterns there, which led to a more rigorous understanding of howthings worked in the heavenly vault. it wasn’t overnight, of course. this tookcenturies. before the invention of the telescope, keen observers built all sorts of odd andwonderful devices to measure the heavens, and in fact it was before the telescope wasfirst turned to the sky that a huge revolution in astronomy took place. it is patently obvious that the ground youstand on is fixed, rooted if you will, and the skies turn above us. the sun rises, thesun sets. the moon rises and sets, the stars

themselves wheel around the sky at night.clearly, the earth is motionless, and the sky is what is actually moving.in fact, if you think about it, geocentrism makes perfect sense that all the objects inthe sky revolve about the earth, and are fixed to a series of nested spheres, some of whichare transparent, maybe made of crystal, which spin once per day. the stars may just be holes in theotherwise opaque sphere, letting sunlight though. sounds silly to you, doesn’t it? well, here’s the thing: if you don’t havetoday’s modern understanding of how the cosmos works, this whole multiple-shells-of-things-in-the-sky thing actually does make sense. it explains a lot of what’s going on over your head,and if it was good enough for plato, aristotle,

and ptolemy, then by god it was good enoughfor you. and speaking of which, it was endorsed by the major religions of the time, so maybeit’s better if you just nod and agree and don’t think about it too hard. but a few centuries ago things changed. althoughhe wasn’t the first, the polish mathematician and astronomer copernicus came up with theidea that the sun was the center of the solar system, not the earth. his ideas had problems,which we’ll get to in a later episode, but it did an incrementally better job than geocentrism. and then along came tycho brahe and johanneskepler, who modified that system, making it even better. then isaac newton - oh, newton- he invented calculus partly to help him

understand the way objects moved in space.over time, our math got better, our physics got better, and our understanding grew. appliedmath was a revolution in astronomy, and then the use of telescopes was another.galileo didn’t invent the telescope, by the way, but made them better; newton inventeda new kind that was even better than that, and we’ve run with the idea from there. then, about a century or so ago, came anotherrevolution: photography. we could capture much fainter objects on glass plates sprayedwith light-sensitive chemicals, which revealed stars otherwise invisible to us, details in galaxies,beautiful clouds of gas and dust in space. and then in the latter half of the last century,digital detectors were invented, which were

even more sensitive than film. we could usecomputers to directly analyze observations, and our knowledge leaped again. when thesewere coupled with telescopes sent in orbit around the earth - where our roiling and boilingatmosphere doesn’t blur out observations - we began yet another revolution. and where are we now? we’ve come such a long way! what questionscan we routinely ask that our ancestors would not have dared, what statements made witha pretty good degree of certainty? think on this: the lights in the sky are stars!there are other worlds. we take the idea of looking for life on alien planets seriously,and spend billions of dollars doing it. our

galaxy is one of a hundred billion others.we can only directly see 4% of the universe. stars explode, and when they do they createthe stuff of life: the iron in our blood, the calcium in our bones, the phosphorus thatis the backbone of our dna. the most common kind of star in the universe is so faint youcan’t see it without a telescope. our solar system is filled to overflowing with worldsmore bizarre than we could have dreamed. nature has more imagination than we do. itcomes up with some nutty stuff. we’re clever too, we big-brained apes. we’ve learneda lot… but there’s still a long way to go. so, with that, i think we’re ready. let’sexplore the universe. today you learned what astronomy is, and thatastronomers aren’t just people who operate

telescopes, but include mathematicians, engineers,technicians, programmers, and even artists. we also wrapped up with a quick history ofthe origins and development of astronomy, from ancient observers to the hubble spacetelescope. crash course is produced in association with pbs digital studios. this episode was written by me, phil plait.the script was edited by blake de pastino, and our consultant is dr. michelle thaller.it was co-directed by nicholas jenkins and michael aranda, and the graphics team is thoughtcafã©.