The Ring of Truth - 6 Doubt

Summary

Highlights

• Cecilia Payne's revelation: Discover how Payne determined that hydrogen is the most abundant element in stars, despite initial skepticism about her findings. 🌟
• Vera Rubin's dark matter: Follow Rubin's incredible journey in measuring the velocities of galaxies, leading to the revelation of dark matter's existence. 🪐
• The joy of discovery: Embrace the excitement and beauty of scientific exploration, as shared by various astronomers in the episode. 🔭

Key Takeaways

• Stars are mostly hydrogen: Cecilia Payne's research revealed that stars are overwhelmingly composed of hydrogen, revolutionizing our understanding of their composition. 🌌
• Dark matter mystery: Vera Rubin and her colleagues discovered that most of the universe's mass is invisible, leading to the intriguing concept of dark matter. 🌑
• Science thrives on doubt: The episode emphasizes that questioning and probing the unknown is fundamental to scientific advancement. 🤔

Overview

Chapters

• 00:00 - 00:30: Funding and Introduction The chapter titled 'Funding and Introduction' outlines the financial supporters for 'The Ring Of Truth'. Major funding is attributed to the Polaroid Corporation, which has a longstanding commitment to pairing art and science to alter perceptions of the world. Additional financial support is received from the Corporation for Public Broadcasting, public broadcasting stations, the National Science Foundation, and the Carnegie Corporation of New York.
• 00:30 - 05:00: The Observatory and Starfield Photography The chapter titled 'The Observatory and Starfield Photography' begins with the mention of Arthur Vining Davis foundations, accompanied by music and applause. Details beyond this introductory segment are not provided in the content shared.
• 05:00 - 08:00: Historical Mapping and Modern Surveys The chapter titled 'Historical Mapping and Modern Surveys' opens with a visual description, comparing a significant round disc of glass to a spoonful of star. This metaphor suggests an exploration of surveying that may connect the historical and astronomical concepts. The imagery sets the stage for a deeper dive into the interplay of light and observation techniques likely used in both historical mapping and modern surveys.
• 08:00 - 17:00: Stellar Spectra and Chemical Composition This chapter delves into the use of telescopic cameras at observatories to record starfields systematically each night. The chapter highlights the significance of heavy glass wedges that imprint vital information onto every captured image, providing crucial insights into the chemical composition and nature of stellar materials. [Music] marks a thematic or tonal transition in the narrative, indicative of an educational or contemplative tone associated with learning about the heavens.
• 17:00 - 26:00: Cecilia Payne's Insights on Stellar Composition This chapter provides insights from Cecilia Payne on stellar composition. It begins with a reference to a small and recognizable cluster of stars in the night sky.
• 26:00 - 38:00: Hydrogen and Helium Discoveries The chapter titled 'Hydrogen and Helium Discoveries' discusses historical perspectives on astronomical observations. It starts with a map of the sky printed in 1603, showing the Pleades cluster—a map created before the invention of the telescope—highlighting the celestial details visible to the naked eye.
• 38:00 - 56:00: Galactic Weighing and Dark Matter The chapter titled 'Galactic Weighing and Dark Matter' discusses historical and modern methods of astronomical observation. Initially, the naked eye could detect only a few stars, with reports of keen observers counting up to a dozen stars in certain constellations. However, the development and global use of telescopes, along with hundreds of observatories, have vastly expanded our understanding of the cosmos. The text emphasizes the transition from rudimentary stargazing to advanced photographic surveys of the sky, highlighting the growth in our celestial knowledge. This sets the stage for discussions on concepts like the weighing of galaxies and the enigmatic presence of dark matter.
• 56:00 - 60:00: Conclusion and Funding Credits The chapter provides a reflection on the advancements in astronomical instruments, drawing a comparison between what the naked eye can perceive in the night sky versus what is now visible with modern technology. A photograph of the Pleiades star cluster is used to illustrate this point, highlighting the addition of hundreds of fainter stars that were previously unseen without instrumental aid. The narrative underscores the transformative impact of these tools on our understanding and perception of outer space.

The Ring of Truth - 6 Doubt Transcription

• 00:00 - 00:30 major funding for The Ring Of Truth was provided by Polaroid Corporation for 50 years we've been bringing Art and Science together to change the way people see the world [Applause] [Music] Polaroid additional funding was provided by The Corporation for Public Broadcasting public broadcasting stations National Science Foundation carnegi Corporation of New York the
• 00:30 - 01:00 Arthur Vining Davis foundations [Music] [Applause]
• 01:00 - 01:30 [Music] the big round disc of glass can you catch a hint of its wedge shape from the play of light that disc is as good as a spoonful of star
• 01:30 - 02:00 in this Observatory the telescopic camera records chosen starfields night after night that heavy glass wedge stamps every image with Clues to the nature of star stuff [Music]
• 02:00 - 02:30 there's a tiny cluster of stars in the night sky that many people know and call the
• 02:30 - 03:00 pleades it has attracted the Curious Watcher for a very long time here is the first of all printed maps of the whole Sky published in 16003 it was brought out at a time before there was any telescope so what it shows us is what the uned eye could see in the heavens it carefully Maps the little cluster the pleades
• 03:00 - 03:30 and there's the pattern half a dozen stars on the engraving for a long time people argued how many could be seen there and with the keenest eyes there are reports of persons who could count 10 or a dozen since that time we have had centuries of use of the telescope and hundreds of observatories all around the world and our knowledge of the sky now is enormously richer look for example at a modern photographic survey of the
• 03:30 - 04:00 whole sky and compare what we now see in the plees the same bright stars are there and with them hundreds or even more fainter stars that the eye can never see that's the kind of change that has occurred with the instruments of the astronomer now here a very strange looking photograph of the pleades maybe you can make out that the pattern is the same and the star do not appear as any
• 04:00 - 04:30 sort of dot or spot but each as a rainbow stripe which we call the Spectrum the photograph was made on the very instrument we watched in use and that instrument Drew out the light of the star sorting it by color across the plate once the physicists in the laboratory had understood how glowing Gas makes its colored lights we learned how to read the recipe the chemical
• 04:30 - 05:00 composition of the Stars by studying the details of these rainbow bands that is why I said that the big wedge of glass which draws the light out into the colors was as good as having a teaspoonful of a plad fetched magically to our laboratory across all those light years Rick Hill is making a comprehensive survey of the sky
• 05:00 - 05:30 he will record all the brighter stars that can be seen from this place before it is over he will have more than 2,000 photographic plates each star represented by a little Rainbow stripe we have to look a little more detail to understand what the astronomers are looking for where the information is so we chose a typical
• 05:30 - 06:00 star from the edge of the plate and enlarg the image now we see quite plainly what the astronomer might look for with a magnifying glass here is the red end of the rainbow band and the image continues along to the blue that band is the spectrum of the star but the features we look for are these fine vertical lines that cross the band of color those are called the lines of the spectrum and it is they
• 06:00 - 06:30 that bear the information about chemical composition oh don't adjust your TV set I have lost my color and the rainbow stripe has lost its color for a purpose notice the information about the spectrum is still there in black and white the color Band still extends from the red end to the blue the spectral lines are quite visible measuring the position of those lines is all the physicist needs to
• 06:30 - 07:00 establish what he wants to know we will show many professional spectral plates in black and white they all still bear the full information of the spectrum and now may I have my red shirt back please lines like these from a star are also seen from known gases glowing in the laborat
• 07:00 - 07:30 this star displays strong lines of hydrogen and lines of calcium too every chemical element makes its own set of specific lines like these a kind of fingerprint but Stars differ in the spectral lines they show compare this one and another one these Spectra show that stars are natural mixtures of many elements different Spectra different recipes
• 07:30 - 08:00 after 1900 a dozen or two accomplished women at Harvard worked over decades to assemble a mighty collection of star photographs the most celebrated of these Pioneers was Annie Jump Cannon her ability to recognize and sort line patterns was legendary the Old Harvard College Observatory became the world's Center for Star Spectra the legacy is alive and growing
• 08:00 - 08:30 the photographic librarian at Harvard Observatory now has access to half a million plates of the sky old and new Allison could we have please that plate that we picked up of cannons the other day this is one of our oldest plates I see a stated
• 08:30 - 09:00 1899 but some years after that it was Annie Cannon who marked one by one these this spiderweb of numbers the Stars whose little Rainbow patches all shown in black and white are there on the plate those are the Spectra that she knew so well how to classify at the University of Michigan Nancy ha has compiling for astronomers
• 09:00 - 09:30 of the 21st century a new version of the spectrum catalog Annie Canon made for the 20th my experiences build up over the years now I've looked at over 100,000 stars and uh this has really made the classification almost automatic it turns out that the eye is really quite marvelous and how consistently it can detect small changes in the uh strengths of the lines Nancy comes to know the line patterns in all
• 09:30 - 10:00 detail process that I go through when I classify a star for the first time is mainly unconscious at this point um looking at the lines in the Spectrum and whether they're many lines or just a few whether they're narrow or broad once I look at the Spectrum then I immediately know a approximately what temperature and brightness the star is and then I look at a standard star put it beside
• 10:00 - 10:30 the other Spectrum to check it out and in about half the cases I actually compare with a standard and in other cases I know the type well enough that a standard isn't isn't necessary for example let's look at number 88 on this plate which is a hot AAR where hydrogen dominates in the star the hydrogen lines that you see get closer and closer together as you go go toward the blue end of the spectrum now
• 10:30 - 11:00 I also uh noticed that there is some calcium in the star and the strength of the calcium would lead me to believe it was what we would call an a15 star and I also assign the spectrum of quality and I would say that this is a really good Spectrum I assign it a quality one 97 is a much cooler Star than 88 you can see that the blue end of the spectrum really fades out and the
• 11:00 - 11:30 strongest um line in the blue is the calcium line but the hydrogen is practically invisible and I can immediately tell that this is an mstar by the time we're finished we'll photograph the entire sky from the South Pole to the North Pole and uh I'll have classified nearly a quarter of a million stars Annie Canon classified them into about 46 groups but I have several hundred categories Nancy brings greater
• 11:30 - 12:00 insight into the meaning of the Spectra than could the Pioneers yet the old groupings were a key step towards the recipe of the Stars Canon placed the Spectra in an order into which they naturally seemed to fall small differences between adjoining pairs but a big difference across the whole sequence the meaning of that order was little understood there were hints but no real Theory the task of
• 12:00 - 12:30 interpretation fell to A Gifted student of atomic physics young cilia Payne her daughter Katherine Haram Andis shares some of her mother's Recollections of those times in the autobiography which she wrote in the last years of her life she did reflect on the uh early years that she spent in Cambridge England in September 199 I entered nunam
• 12:30 - 13:00 College Cambridge the atmosphere was euphoric the war to end war was over few Among Us young people doubted that the Millennium was upon us the intellectual atmosphere was equally heady the new physics was gaining momentum radioactivity was in the air it dominated the Cavendish laboratory for Rutherford was beginning his attack on the atomic nucleus the bore atom was introduced to us by
• 13:00 - 13:30 bore himself The Lure of the Cavendish laboratory was irresistible and you can just see that that's really how she felt Cecilia's grasp of the new Atomic physics allowed her to unravel the Spectra and substance of the Stars the advanced course in physics began with Rutherford's lectures I was the only woman student who attended them and the regulations required that women should sit by themselves in the front
• 13:30 - 14:00 row at every lecture Rutherford would gaze at me pointedly and would begin in his stentorian voice ladies and gentlemen all the boys regularly greeted this witticism with thunderous Applause stamping with their feet in the traditional Manner and at every lecture I wished I could sink into the Earth my mother really felt that for her to pursue any kind of scientific career in England there were virtually no
• 14:00 - 14:30 opportunities at all I think that was a large part of her decision-making process that made her find a means to come to this country so that she could progress on in the field that she had chosen although in those days as a woman it was unlikely for her to have a professional position she determined that she was going to have one at Harvard when she came there was an environment where she could learn a great deal and put into practice some of the things
• 14:30 - 15:00 she had learned about at Cambridge University and so she wanted to put those two things together and here was a perfect local if Harvard was the right place to come Cambridge University in England was about the best place to come from for it had been 10 years since bore and Rutherford working sometimes together had formed that theory the quantum theory of the atom which lay behind any attempt to understand the Spectra and
• 15:00 - 15:30 substance of the Stars Bor and Rutherford began with the simplest atom of all hydrogen they could explain all the lines in its Spectrum every kind of atom has only certain discrete energies in which it can exist when an atom takes up just the right amount of energy it goes up to a higher level when it falls down it can give off the energy as light we map the energy levels in a simple diagram a Quantum ladder this is
• 15:30 - 16:00 the ladder for hydrogen even the simplest of atoms has many levels every color of light has an energy to match so its energy jumps determine the colors any atom can emit or absorb the jumps make the lines of the spectrum atom by atom line by line in outline that is the theory Cecilia would
• 16:00 - 16:30 apply to the complex Spectra of the Stars she felt that with that key the quantum ladder and its identification not of one but of two levels that go with every spectral line she could perhaps for the first time find out the recipe of the stars in a chapter entitled Harvard College Observatory she says when I arrived in Cambridge Mass Metts I had
• 16:30 - 17:00 crossed a gulf wider than the Atlantic Ocean abstract study was a thing of the past now I was moving Among the [Music] Stars the day after I arrived I was installed at a desk in the brick building then the newest structure in the observatory grounds it had been bu to house the great collection of photographic
• 17:00 - 17:30 plates when I first looked at the plates I was amazed the Spectra looked like tiny parallel smears it seemed impossible that anyone could see enough in those tiny smears to classify the Spectra sometimes indeed I would find one of Miss Cannon's numbers in a spot where I could see nothing but a faint blur here she was ready to analyze the substance of the Stone
• 17:30 - 18:00 she looked at the old Spectrum in a new way she had two tasks first of all she wanted to judge whether a line was weak or strong she did that by ey simply comparing it to the other lines in the photograph second of all she had to be sure she understood every line that is to say she had to place it in its proper interval on a Quantum ladder this was a plate Cecilia Payne actually used each of her red marks points to a line she identified as coming from a particular element a few are clear many are faint from the
• 18:00 - 18:30 relative strength of different lines she hoped to figure out how many atoms of each element were present in the glowing gas of the star it was clear that some quantitative method must be devised for expressing the intensities of the spectral lines and I set up a crude system of eye estimates next came the arduous task of estimating their intensities on hundreds of Spectra there followed months on almost a year as I remember of utter
• 18:30 - 19:00 bewilderment often I was in a state of exhaustion and despair working all day and late into the night finally some light dawned in the darkness look at the content of pay's argument with the atomic theory of the day an example is a violet line she reported coming from the element calcium now it's not an everyday ele you'll see pure but we all know it's a
• 19:00 - 19:30 major constituent of bone and shell an essential part of the human diet and it of course its lines occurred and it was well known in the spectrum of the stars but this particular line she knew more about she knew that it occurred when a resting atom of calcium in its lowest possible State picked up just the right energy to jump to the first strung of the ladder she watched that particular line not any line of calcium that particular
• 19:30 - 20:00 line of calcium in Star after star arranging the sequence to look say at the coolest barely red hot Stars up to the hottest blue white stars had observed a strange but absolutely unmistakable regularity in the cool stars that line was strong in the hot stars that line
• 20:00 - 20:30 was weak some people thought that meant there was no calcium in the hot Stars they were different and just didn't have the element that's not the case you can understand it quite well from the theory if the star is cool say only red hot most calcium atoms are down there in the lowest resting state thus in cool Stars this line of calcium is strong for almost every calcium atom present is in the right state to start the jump but in
• 20:30 - 21:00 hotter and hotter Stars those clim atoms can pick up more energy some of them spread among the many higher States fewer calcium atoms remain in the right starting state to make this line so the calcium line that she identified this particular Violet line is strong in cool stars and get systematically weaker as the stars get hot she could treat that quantitatively she you could find out what the temperatures would have to be
• 21:00 - 21:30 in the stars and the whole picture became more and more consistent the calcium atom was not an exception many other atoms behav the same way it's even more understandable perhaps if we look at a contrasting Case by Chance the contrast is another blue violet line a line of the element hydrogen as one looks first at cool red stars and then step by step up to the brightest blue white stars this hren line goes from relatively weak until it
• 21:30 - 22:00 is very strong just the opposite of the behavior of calcium the hydrogen line that we're looking at is not a line that comes from the lowest state of hydrogen up to the next state on the contrary it begins in state number two and jumps well above that but the atoms of hydrogen in the cool star cannot be up there in state number two they're very rarely there because they are all in the bottom State not much excited by the low temperature
• 22:00 - 22:30 only as the temperature rises can there be more and more atoms that temporarily feel some light or some collision and push them into the second state but only those atoms can give rise to the line she saw therefore it makes very good sense to say yes in this particular line not for all lines of hydrogen this particular line will be weak in cool red stars and strong in hot blue white stars and so it is two years of estimation
• 22:30 - 23:00 plotting calculation and the work I had planned was done I had determined a stellar temperature scale and had measured the astrophysical abundance of the chemical elements Cecilia Payne's work in those years had a remarkable outcome she expressed it nicely in her thesis which people have called and I think they are right the best thesis ever written in astronomy she showed that most stars are made up according to one grand
• 23:00 - 23:30 recipe the different Spectra come mostly from different temperatures of the glowing gas but more than that she found something so startling that she herself and her advisers could not quite believe it those hydrogen lines which were strong as the lines of calcium even though they came only from the rare High Ling atom of hydrogen demonstrated from her calculations that hydrogen was a
• 23:30 - 24:00 million times more abundant atom for atom in the typical star than calcium a million atoms of hydrogen to one of calcium cilia acted with the justifiable caution of a scientist using a new theory for the first time she wrote the outstanding discrepancies between the astrophysical and terrestrial abundances are displayed for hydrogen and helium the enormous abundance derived for these elements in the Stellar atmosphere is
• 24:00 - 24:30 almost certainly not real but now we believe she was right in the first place the difference is real the universe is hydrogen rich in fact all that we can see out there everything that glows seems to be made primarily of hydrogen that was a remarkable result it is now a commonplace of the astronomer but then it was revolutionary
• 24:30 - 25:00 Cecilia pay gashin had a long and celebrated career she was the first woman ever promoted to professor at Harvard her decisive work had shown that the stars are made according to an unearthly recipe though the mix includes most of the elements we know almost all of it more than 90% is hydrogen it's more important even than it sounds it's not just it was unexpected and something of a blow to us to find that the matter we saw around us
• 25:00 - 25:30 every day was not the right sample more than that think of the two atoms that are so abundant hydrogen 90% helium making up most of the rest not just any atoms hydrogen is the simplest and lightest atom that can exist stably and helium is the second simplest and lightest matter is fundamentally simple somehow Young pristine that's what we seem to see in
• 25:30 - 26:00 this result and every theory of the origins of the universe will have to come to grips with that fact all the stars we see including our own Sun are hydrogen rich but most of space seems dark between the Stars nothing glows to eye or camera in the years after World War II the new
• 26:00 - 26:30 technology of radar and radio was put to astronomical use to search for radiation no eye can see the first Hydrogen signal from the darkness was picked up in March 1951 by doc Yuan a grad student fresh from the Navy and his adviser Ed purcel the two men took us to the roof of the physics Lab at Harvard where they had excitedly made their discovery long before I think
• 26:30 - 27:00 it's right here Ed I think this is the one here one came out right and we just took the glass out put the horn the throat of the horn in there and looked out here to the South this old horn is a microwave antenna able to pick up weak signals from space originally we didn't know whether the radio waves uh would actually uh be detectable and uh the only thought at the time was if they were they probably would be concentrated somewhere along the Milky Way and as a result the best
• 27:00 - 27:30 place to be looking would be toward the south in the vicinity just north of Sagittarius which is the center of the Milky Way or our galaxy and uh just take a chance on the fact that there is a great concentration of material there well actually a good deal had been deduced from rather indirect evidence by the astrophysicist concerning the gas in our galaxy and people knew it was mostly hydrogen and that it was very uh empty
• 27:30 - 28:00 there very few gas atoms per cubic centimeter and in this empty thing they're emitting this very faint very characteristic radiation Yan and purcel opened a whole new window for astronomers their receiver detected a spectral line of hydrogen that occurs as a radio wave hydrogen atoms emit light by a jump down the quantum ladder from a higher energy state to a lower one it is no different for this radio jump but the starting
• 28:00 - 28:30 state known as the hyperfine level is so close to the lowest state that you have to magnify by a millionfold to see the tiny separation even from the coldest regions of space hydrogen can send out such low energy emission the amount of hydrogen out there and its temperature was such that the radiation at this frequency that we're concerned with this
• 28:30 - 29:00 very special frequency amounted to only one watt landing on the entire Earth to attempt to detect a signal of that intensity less than um a million millionth part of a watt as far as what I was dealing with uh would be extremely difficult even building an excellent radar receiver I was concerned that we might be dealing Downstream somewhere with a negative thesis and the negative thesis
• 29:00 - 29:30 is extremely difficult and could take an extra year or two uh to tidy up and calibrate and put some numbers on it if you don't detect something then you must carefully State at what level you're capable or incapable of detecting it so uh that was my concern Ed's comment to that was so it's a couple of years of your life and uh but it's certainly worth it and if you do Ed you'll be in Life magazine and he was right he
• 29:30 - 30:00 did forel BET right though doc still had to work hard to succeed well as I remember it was in the morning so he'd been up all night and I'd been at home in bed and as I remember he said I think I have a thesis and I came dashing over it was over the weekend of uh uh Easter and the first time it was turned on the
• 30:00 - 30:30 scanning was such as there was tuning looking for this hydrogen hyperfine station broadcasting from space I was tuning through the Spectrum as you might just turn a knob and I noticed at the end of the first scan the signal was on its way up and here on the esterine paper from the esterine Angus recorder you know it looked this wiggly line looked as though there might be some bumps in and we rolled out about 20 ft of it and got down and sided along it
• 30:30 - 31:00 you see and then we can see this pump like that it's just the way you designed it it's just the way you thought about it there's just a chill goes up your back and you say I got it and you just never ever forget the excitement of doing something like that and yet it's so common in the field of science to go through these steps and feel that excitement it's just
• 31:00 - 31:30 [Music] beautiful the space between the stars is filled with thin cold hydrogen gas that horn had caught the [Music] signal The Next Step required an instrument carried above the atmosphere George KS of the naval research laboratory I think that uh those who have seen some
• 31:30 - 32:00 of the film clips that were included in the movie The Right Stuff will uh remember that many rocket launches were failures in the early 1960s and the sounding rockets for scientific purposes were no exception we often had to launch three or four rocket experiments before we were able to get everything to work properly not only did the rocket have to go above the atmosphere but it also had to have an attitude control control system that pointed it at the stars that
• 32:00 - 32:30 we wanted to look at with sufficient accuracy and also the time that was available in sounding Rockets was very short only a few minutes KS knew that on Earth most hydrogen gas is in molecular form twin hydrogen atoms linked together no earth-based astronomer can hope to find the sign of molecular hydrogen a strong line in the ultraviolet its radiations simply cannot penetrate the atmosphere was molecular
• 32:30 - 33:00 hydrogen common in space too KS was the first to find it there in [Music] 1970 18 in early 1986 George came to the White Sands Proving Grounds ready to launch his ultraviolet detector again this time he would seek hydrogen in Comet H 6 5 4 3 2 1
• 33:00 - 33:30 we did it got sequence you should start having film trans we're maneuvering now I think the unique features of our instrument were that it had Optics which were specially designed to be sensitive in the very short wavelength range of the ultraviolet where molecular hydrogen has its spectrum and second L it was an electronically intensified camera system
• 33:30 - 34:00 which was much more sensitive than conventional photography by the dawn's early light the astronomers set out to recover their rocket one of the most exciting things about sounding rocket research is that you can be involved in virtually all aspects of it from the construction of the payload development of the instrumentation to actually obtaining the data and analyzing it
• 34:00 - 34:30 [Music] we were always excited to be able to get some data from a sounding rocket flight since we knew that it was something unique that no one had ever seen before that delicate gear has survived a 100 mile fall they rumage inside to lay hands on what counts the record of what the spectrograph saw in the case to the molecular hydrogen we knew that the rocket
• 34:30 - 35:00 experiment was a success but it took several weeks of uh looking at the data before we really could say that we really Sol the molecular hydrogen in the Spectrum hydrogen and helium are everywhere the glowing nebula are made of hydrogen where the hot stars make the gas Shine the giant planets are made of hydrogen and helium when we look with new methods
• 35:00 - 35:30 into the heavens we see hydrogen one way or another the radi astronomers report hydrogen in the cold gas of space and even the rocket born detectors bring back the news hydrogen in a new form whichever way we look and wherever we look we see the same thing a universe in which the simplest atoms dominate the population [Music]
• 35:30 - 36:00 that's a very important conclusion we want to have a lot of confidence in it is there any other way we can look even roughly at that problem there is a way it is a commonplace Earthbound procedure familiar I think to prudent Shoppers for centuries it is the way of weighing here I have two containers from the shop they each have the same label
• 36:00 - 36:30 vanilla ice cream one pint they look about the same supposed to be the same material can we check the recipe in any fashion without even looking into the carton we can it's a good deal heavier we have found something out without looking this method can detect the invisible if inside this carton there is
• 36:30 - 37:00 a light ingredient more abundant there than in this carton that's all we can say we cannot be very subtle about it those who know ice cream will recognize if I add the hint this is a more expensive carton that they might know they may know what that ingredient is but we can't tell from this crude but powerful method of seeing the invisible to go beyond we need a more subtle procedure for testing not very astronomical what the astronomers have
• 37:00 - 37:30 to do is to find a method to weigh plenty of stars our universe is built out of big collections of stars that might be weighed they are the galaxies plenty of them far beyond the stars of the night sky a typical big Galaxy contains some 100 billion stars orbit there under the gravitation of the star crowded
• 37:30 - 38:00 Center so I'm I'm game to start with 274 astronomer Vera Rubin and her colleague John Graham of the Carnegie Institution in Washington have come to Kit Peak National Observatory to work with the biggest telescope here I told them that's where we'd be working most of us I that is quite easily visible well go out and take a look yeah astronomers compete for a turn on this powerful instrument a few nights at a time once or possibly twice a year I
• 38:00 - 38:30 have binoculars up in the Dome the 160 in telescope can catch light enough from distant galaxies to produce the detail you need to weigh one of them Vera and John have three nights if the sky stays clear they might image a dozen carefully chosen galaxies oh that looks good yeah that looks very good telescope time is
• 38:30 - 39:00 very precious so that you must come with a very well defined observing program you know what you're going to do you think you know what you're going to do every every hour or so go let's go sure make it night yeah make it night ready for the integration to start it may take something like 10 minutes to set up on the Galaxy you have to turn the telescope you have to find it these are very faint things here's the Galaxy we're at the
• 39:00 - 39:30 object there you are oh that's pretty good that's that's nice typically the exposures that I make take two hours you have to be very careful not to make a mistake because you don't want to spend two hours looking at the wrong object okay I'm Center it up okay time to time to go you'll get a guide star I'll set up for the observation this will be picture 168 your face with the problem if there's one object that you very very
• 39:30 - 40:00 much want to study whether you do it the first night even if the night is pretty poor or whether you gamble and hope that the next nights will be better and so there's a lot of juggling that goes on you you work very very hard at a time when you would normally be sleeping but if everything works works well it's it's quite an exhilarating experience right to the next ver can indeed weigh galaxies even though there is no way to put a Galaxy on a pair of scales she uses what we know about gravity one of
• 40:00 - 40:30 the things that Galileo really understood is that the speed with which something Falls is not dependent on how heavy it is this rock is is attracted to the Earth and Falls not because of the amount of matter in the Rock but because of the amount of matter in the earth if if I take a rock and just drop it it'll just fall at my feet If instead of just letting it drop I I give it a little forward motion it'll fall in the trees
• 40:30 - 41:00 over there if I if I throw it very very hard it will get to the mountains or perhaps to Los Angeles and so here's the earth a globe and I'm I'm throwing this rock and it it would fall straight down or it would fall over here it would fall in Los Angeles or perhaps even Japan but if I push it very very hard it will be falling but the Earth is curving away and The Rock will fall and fall and fall but it will continually miss the Earth
• 41:00 - 41:30 it will actually orbit if I could throw it far hard enough it would go completely around the earth come back and hit my head 250 years ago Sir Isaac Newton drew the very Earth orbits Vera described we set the illustration from the old book into motion Newton explained how a body that orbits the earth is controlled by the amount of matter in the Earth by measuring the speed in orbit and the size of the
• 41:30 - 42:00 corresponding orbit Circle you can weigh the central gravitating body the planet Earth you find the same weight for the Earth whether you figure from the smaller orbit or the larger one from the much bigger orbit of the moon or even the tiny path of a falling Apple the planets of the solar system offer the same opportunity for weighing you measure the speed in solar orbit for Mercury Venus Earth Mars notice how their orbital speed is the slower the
• 42:00 - 42:30 farther out the planet circles using those speeds and orbits we can weigh whatever mass is pooling on each body in turn about all the matter we see there is the bright massive Central Sun this scheme of Newtons should be able to weigh a Galaxy as well as a planet or a sun astronomy developed with Scientists with astronomers who were familiar with the solar system they understood the sun
• 42:30 - 43:00 they understood the Motions of planets it was natural therefore to assume that when you looked at a Galaxy the center was very bright and the outer parts were very faint and so the the presumption was that when you looked at the distribution of light in a galaxy you were looking at the distribution of mass and therefore astronomers had expected that stars near the center of a galaxy would be orbiting very rapidly and stars at the outside would be going very slowly like Pluto by the mid 60s there
• 43:00 - 43:30 existed image tubes electromechanical optical devices which enhanced the incoming light to a telescope and it made possible for the first time to really study the velocity of stars way out in a Galaxy where the light is very very faint but galaxies are huge Stars take a couple of hundred million years to Circle once around their Galaxy as we believe our son does you just
• 43:30 - 44:00 can't wait around to record such Majestic motions instead Vera exploits a different kind of speedometer the wonderful phenomenon we know as the dopper shift our film crew sets up but more in the round circle okay something like that first we fasten the microphone right
• 44:00 - 44:30 onto the electronic tone maker in the coffee can test [Music] test the attached mic shows that the steady pitch made by the tone maker is not affected by The Swinging itself
• 44:30 - 45:00 but when we use a stationary microphone some distance away the tone it picks up is dramatically different the relative motion of tone maker and microphone entirely Alters what we hear now the tone warbles as the source moves the pitch is higher whenever the source approaches
• 45:00 - 45:30 lower when it recedes listen as we selectively sample the [Music] sound left right and in
• 45:30 - 46:00 between the shift from a single fixed note on the staff measures the speed of the tone maker as it revolves the same phenomenon can measure the speed of a star in orbit but the effect must be sought not in the pitch of a tone but in the color of light [Applause] Vera invited me to her home base in Washington where she shared the results
• 46:00 - 46:30 of many years of observing so this is the sort of Galaxy you've been weighing that's right here one of the nicest is NGC 7541 oh that is yes let me show you what that looks like this is the Galaxy and in the sky that is it's in Pisces or behind P I can also trans form it to an image that's white on on a black Sky which is a nice
• 46:30 - 47:00 way to look at it and then I can transform the image so that here we're seeing just the very bright parts of the Galaxy here we're seeing the Galaxy pretty much as we observe it those bright patches are not Stars no these bright patches are luminous gas clouds surrounding whole groups of stars and they're radiating strongly in the line of hydrogen Alpha that's actually the the way we study them at the telescope I
• 47:00 - 47:30 put the slit of the spectrograph across the center of the Galaxy like this so I'm getting light just from this region from these faint outer regions the nucleus and over here we don't go quite as far so one end you're getting light from the other end way out there somewhere down here let me show you what the Spectrum looks like this is a small portion of the red region of the spectrum here's a copy of
• 47:30 - 48:00 it normally you've been looking at Spectra that looked like this with the red in this direction the blue several feet over in this direction the Spectrum from Blue to Red would be five or 6 feet long if you had it all just picked out the part you want which is a red part that's right and this is this strongest line is the hydrogen line in the red and that's from the glowing gas clouds that we saw in the galaxy and here's the hydrogen line and this Jag is due to the
• 48:00 - 48:30 doppers ship we heard the Doppler shift as a shift in Pitch when Vera looks at the Spectrum she sees the Doppler shift as a small shift of position in the lines every spectral line is shifted slightly blueward as the source of light approaches but towards the red as it recedes here's the Spectrum which we get when the slits across the Galaxy these three
• 48:30 - 49:00 knots come from three emission knots out here with the faint emission faint hydrogen coming from this region of where we see the faint Galaxy on the other side of the Galaxy the most notable region is this where we have no hydrogen Alpha that's where the dust in the galaxy is uh preventing the background light from reaching us this side is coming toward us these um the
• 49:00 - 49:30 the emission on that side is shifted toward the blue the same hydrogen it's making the same wavelength on either side but we see it differently because it's moving toward us or away from us that's right which way is it going yes the the left side is coming toward so it's circling around so so we're sort of mapping the velocities Vera has measured the shift in color for each distant star Cloud at the two ends of its galactic IC orbit at one side coming toward us at
• 49:30 - 50:00 the other side going away the speed she records remains about the same or even grows a little larger as the light is sampled farther and farther out from the center in the solar system planets near the sun orbit fast but planets farther away move more slowly from the speeds we measure we can reckon the weight within each circular orbit for the solar system we find that the same weight attracts Mercury Venus Earth
• 50:00 - 50:30 or Mars that must be the weight of the Sun itself all we can see what the dust or the Comets or the other planets contribute is too small to notice what we see is what we get but when we make the same sort of weight calculations using speeds measured in orbit around that Galaxy the result is astonishing and if we now just plot the distri distribution of matter here's what we get and what we
• 50:30 - 51:00 see is that the mass of the Galaxy rises from the center and as you go further and further out you include more and more mass still finding more and more mass it's even Rising here by a considerable amount of weight even though there's almost no light as I can recall in that part of the Galaxy in fact out here where you see almost no light there's all that Mass all that weight is growing still way out there though there's no star light that's
• 51:00 - 51:30 right the weight is not shining that's right that's right these the Stars way out here are going very fast in response to a gravitational pull from something that's not bright not bright at all and we don't know what that is astronomers have worked hard to try and see if they could find even faint stars and we we see nothing all we're seeing then all the bright light and all the hydrogen lines are coming from from
• 51:30 - 52:00 a small fraction of the matter that's right of the weight in the in the universe I've I've said recently that nature has played a joke on astronomers we we became astronomers thinking we were going to study the universe and we now find we're only studying the five or 10% of it that's that's radiating it's just the the icing on the great cake that's right somehow the bulk of the weight that controls the orbits in the Galaxy just does not shine in any color of
• 52:00 - 52:30 radiation we know the same result has been found for a 100 galaxies everyone that has been studied well enough to weigh including our own that's useful that's that's a that's a success that's a success it's morning it's morning and we're done when I first started observing significant number numbers of rotation curves of galaxies it became
• 52:30 - 53:00 very clear that none of them none of the Stars far out in a galaxy had low velocities that was totally contrary to expectation it was not terribly hard to accept because the observational evidence was so clear there are many problems in astronomy at the present time where the observational evidence is very complex you have to go through lots of arguments you have to do lots of uh data handling before you come out with
• 53:00 - 53:30 the answer in the in the case of the rotation curves that's not really so you can look at the observations just as it comes off the telescope and you know that what you're seeing is what is happening we now know that in every Galaxy we study the stars at very large distances are moving are orbiting with very high velocities and that tells us that there is a lot of matter at very large distances from the center so we
• 53:30 - 54:00 see a lot of matter where we don't see very much light and that has led to the concept of dark matter we now think that a Galaxy consists principally of Dark Matter perhaps even 90 95% of the mass quite a science has changed a lot since Cecilia Payne did her work although she found it difficult to get her results except Ed once they were accepted everyone said that's what they knew that was a fact the present
• 54:00 - 54:30 observations tell us I think that there is an enormous amount that we don't know and that the more we observe the more doubts are raised we we don't know what the dark matter is we don't know how much there is but I think that's really part of the fun of doing science I think it would be I don't think it would be as much fun to do science if you got an answer and that was the end of it so I think that the the doubt is healthy it gives us it gives us a wide range of
• 54:30 - 55:00 problems to to advance to and I think perhaps the best thing that you can do as an observer is to find out something that shows you that you have to do more observing and learn [Music] more for 50 years the news was good every new channel we opened up to look into the cosmos brought back the same confirming message yes the material out
• 55:00 - 55:30 there is mainly hydrogen it was Secure we liked it and it even made a great deal of sense the simplest of materials but Vera Rubin and her Associates worldwide with their new techniques and their ingenious experiments have changed it utterly strangely they didn't even say that we had been wrong it is true that everything we see out there is hydrogen but there's 10 times more they tell us that we don't see at all all how that can be no one understands is there
• 55:30 - 56:00 something wrong with Newton's gravitation so our inference about the weighing is in error it doesn't seem likely it's possible is there a way of packaging hydrogen so that it doesn't glow in any part of the spectrum we can examine again no one knows how to do that perhaps there's some new kind of matter unsuspected on Earth left over from early stage of the universe that doesn't glow at all but only pools and ways that too is possible if you ask me what the universe is made of now I have to
• 56:00 - 56:30 say I remain in great doubt I just don't know but one thing I do know we will try very hard to find out [Music] [Music]
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