 an especially interesting topic because we didn't realize that the cluster of stars that we see around us are actually a majority of them are really just galaxy which is just an island gravitational island in the universe structure of the universe it's pretty all inspiring because yeah i'm looking at it here less than a hundred years ago so 1923 is when edwin hobble found a sephid variable and my audio got screwed up on that episode but maybe it's still worth checking out the episode on edwin hobble i did a few back i tried to explain this discovery we're gonna start with the andromeda nebula the rest of the galaxies this study guide created by david butler the actual science of astronomy in a very i'd say a very asmoresque tone and style so i would future self will remember to put the link in the description and i'll try to use this book visible to the naked eye and studied by persian astronomers around 980 the andromeda nebula was thought to be a part of the milky way which makes you wonder what it is that i think it's pretty interesting that it's uh it's like analogous to analogous to being in a cave what's right in front of you and four years i'm sure we were as a species we were looking into the sky and we're seeing the infant stars in yesterday in cosmological last minute a minute ago in cosmological timescales we discovered that we're in this galaxy that's a hundred thousand that takes light a hundred thousand years bras but nothing compared to the actual scale of the universe that we're aware of now and uh oh i guess i should look into how far away we thought distant object prior to that actually was i i think reading something like 200 000 years light years i think that a million light years was completely out of the question so um to me that's just fascinating that we our perspective on the universe has changed so drastically just such a short time ago it's amazing but let's move on initiated the cosmology and he uh found this sephid variable the star is called v1 here's a shot of Edwin Hubble's image of andromeda which he uh made four by five inch tober sixth he originally identified three stars and marked each of them with a n for nova he thought they were exploding stars but later he realized that the nova at the top says var exclamation point was actually a sephid variable and that's what i'm gonna look up real encyclopedia so he uh once he realized that he crossed it out and he crossed out the end so the reason he added the exclamation exclamation point was because he knew that this variable would allow him to calculate the distance cosmology back then i mean still really is still really is like how exactly how certain objects are it blows my mind that just how far away sephid variables are based on their um their characteristic periods and so we know that let me look it up real quick so this uh period of the v1 sephid variable star four days before v1 distances to stars were measured in thousands of light years but after v1 the universe got much much bigger using his um what i'm about to show you he realized that the universe v1 was over two and a half light years away so that's that's amazing that he was measuring it just thousands or tens of thousands of years light years and all of a sudden the science the facts that he was so used to just the distance of a couple thousands of light years flashes of insight you're given if you uh stick it out locations series sephid variables okay page 42 i just think that picture is so amazing the cgi that discovery channel shows like that use nowadays they're they're getting better but uh kids the those shows are they used to really impress me but uh they seem to be just a lot more scientifically as someone like david butler gets sephid sephid variables here excerpt about this and studying the Magellanic the distances of these clouds were on 50 kilobar sex distant clearly sufficiently remote for all their stars to be considered at the same distance you notice that the brighter sephiates and because of their equal distance this showed the existence of it or one sephid was required to determine the absolute studies of star clusters in the early 1960s established that the relation reproduced in figure 2.29 classical sephid is uh w virgin w virginus and rr lear what this is the distance of the sephid close to 100 days for sephid classical sephid to say they were standards set in practice and maybe there are that would be really interesting if there are i got there's a couple you out there is set to a certain standard luminosity and the distance of it to uh to an approximate distance just be some equation some function oh it's standard absolute luminosity so if it's just a little bit dimmer you know that you're much closer to the lighthouse and shore than otherwise think and if it's very very very dim then you have a good idea because the period won't be consistent i guess it's really cool that that's the one was definitely too far away to be a part of this also meant that uh because it was a part of the other stars and that nebula had to have been that same distance as well so this may be important stars in the history of cosmology just can't get enough of that so andromeda is a is a beautiful barred spiral galaxy with two spiral arms that glow massive number of new stars this is a lot like our milky way years ago i guess just barely justness in our brains evolved significantly physiologically we created and lost great civilizations and we built telescopes that caught the light when it finally reached our planet andromeda has a i guess i assume all galaxies has a central black hole here we see the lermas black hole at the center of andromeda this is the sharpest visible light image ever made of the nucleus of an entire external galaxy you can see here the uh there's a blue glow around the center of what happens to be a double nucleus full space telescope astronomers were able to identify the source of the blue light surrounding the supermassive black new spectroscopic observations revealed that the blue light consists of more than 400 stars so tightly packed our star sun is four light years away so zero dark skies if you're a planet on those stars which i highly doubt too chaotic to have developed life i suppose so the disk is nested inside an elliptical ring of older cooler redder stars stars are at the farthest point so they give the illusion of a second second nucleus so deep inside the black hole's gravitational grip now they survive in such an extreme environment that young stars are so closely bound to the central black hole suggests that it actually might be a there's a total of 54 galaxies in our local group andromeda is the largest the milky way is the second and triangulum is the third 16 satellite has 25 members of the group aren't gravitationally that sentence that didn't really make sense i guess here we have the just 2.85 million light years away so it's the third largest member of our local group thousand light years so half is which is a lot but this next small irregular galaxy is one of our closest neighbors it's actually considered prototypus fragmentary galaxies that uh existed and it is that gc 6822 is unusually high as it's unusually high abundance of it's on h2 or hii i don't know enough that's supposed to be roman numerals um the region emission nebula these are visible surrounding the smaller galaxy particularly towards the upper right and we can see up there it's okay so light years away novel suspected it might belong to our local group but it wasn't confirmed until he weighs galactic planes the 16 of them just orbiting our this map shows the closest dwarfs they're all gravitationally bound few tens of millions of stars is insignificant compared to the number of stars in our galaxy sagittarius dwarf is the closest and in fact it's interestingly being slowly ripped apart by our galaxy is the furthest away and has six globular clusters orbiting it see if i can so in our book here it looks like the only section on the local group most of their distances are a sephia variable reasonably mixed sample of galaxy types except that there are no conspicuous giant ellipticals hard to establish the precise helpful class for our galaxy because we're inside it and so we don't easily see its large scale structure the galaxy has several small Magellanic clouds clearly visible one and they say that there could be many more de galaxies really sure what do you mean more distant from us in very faint see what the copyright for this book was give us an indication of how up to date it is although i can't imagine that the science has changed for our local group at least much i can't imagine we've discovered a whole lot like more things that would fundamentally copyright date but it does say that uh does say that since the derived data used throughout this book are adopted by the 16th congress of the international astronomical union to granobal in 1976 so that does make sense as you can see that a lot of that pictures are monotone as of this book proper motions of galaxies are information of velocity and from this it is evident that the local group galaxies are all in orbit observation suggests that the system is not gravitationally stable and will actually break up eventually that's really that's i think it's always really interesting because there's so much consistency and constant motion in the skies and the stars and the planets and that appears to be order because it's observed on such a small time scale by us distant galaxies in the local group the distances are not so accurately known so the membership is uncertain it's generally assumed that the group includes all galaxies of a distance to one mega parsec which which i think parsec is i guess i could look it up sure i want to say it's short for pc parsec is the other way around to the 13th roughly the parsec is analogous i guess to a foot to a yard so one mega one million parsecs would be three million which makes sense i guess okay let's see if i can galaxies near the galactic plane suffer obscuration principally bright nearby galaxy therefore could be heavily reddened and appear faint galaxies are known some of which are probably in the local group some vaguely interesting stuff in there and so to return to our study sheet to us as i just said the large and small Magellanic clouds can be seen in the southern sky written 70 000 light years away small is a thousand right mc for short is the brightest galaxy in our sky contains several billion stars and many stars are still forming the small Magellanic cloud or smc for short contains at least several hundred million stars like the lmc there's still a lot of formations taking place in it an interesting little fact about our galaxy is that based on supernova n 63 a in 1987 a they were listed about 160 000 light years away the furthest 160 000 light years is in fact further beyond the extent of our milky way because the large melancholynic cloud so close there's a lot more beautiful nebulae inside it that we can actually see and we have berry in this image 0 59 67 point of nasa's great observatories shondra x-ray so the result shows soft green and blue hues of heated material from the x-ray data surrounded by the pink representative of the ambient gas being shocked by the expanding blast wave and what's even crazier is that we quite observe the movement of it that's really cool the relevant we slowed things down a lot we'd see bacteria living out long long lives we sped everything up we'd see and galaxies entire galaxies and groups local groups like ours orbiting that's around the star into each other and exploding uh well i guess not really exploding but certainly being torn apart ripped bc 20 74 which is about 170 000 light years away this region is a firestorm of raw stellar creation perhaps triggered by a nearby supernova explosion looking image reveals dramatic ridges and valleys of dust the serpent-ed pillars of creation and fiercely traviolet radiation so the region is on the edge of a dark molecular cloud as the incubator for the birth of new stars and lastly i just wanted to show you that the local group is in fact native as these astronomers are we'll explore this local volume if i get to it