How Do We Know What Stars Are Made Of?
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- เผยแพร่เมื่อ 20 ต.ค. 2024
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Pin-pricks in the celestial sphere, through which shines the light of heaven? Or gods and heroes looking down from their constellations? Or lights kindled above middle earth by Varda Elbereth and brightened with the dew of the trees of Valinor? Science has long pondered the mysteries of the stars. This is how we finally figured them out.
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Hosted by Matt O'Dowd
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Congrats Matt!
"Lehman Associate Professor Matthew O’Dowd was awarded a five-year, $2.94 million grant by Schmidt Futures to study the structure and evolution of the universe, black holes, quasars and dark energy"
Wow! Now THAT is awesome! A smart person actually given an opportunity in this shitty country.
I'd spend 5 years partying and then write 42 on an A4 sheet
@@sylvain7277 based
@@ikaros4203 god damn you rick rolled me as soon as I clicked on your profile picture xD and then those 2 big eyes stared back at me as I sat there wondering what had I just done to deserve this. Nice profile pic though.
source pleasee
0:54 I tip my hat to video editor for highlighting Matt's right side when he's "close to the star". You're true pro, sir/madam.
I went back and had to check that out after I read your comment that’s some attention to detail there ain’t it! @Franko
It's not "his" right side; it's his left side, on the right side of the screen with respect to the audience. Details. :)
@@deepfriedsammich you bet your wife that video wasn't flipped around vertical axis during editing? Sh!teater
@@Dro210 thank you, appreciated )
@@DrSardonicus well now уоu can dіе peacefully, loser
Seeing a doctor in physics wearing a "Periodic Table of Minecraft" shirt is just hilarious, lmao
구 Felix. I like how whoever designed the shirt put *beta in the asterisk at the bottom as if they knew Minecraft was going to have more blocks.
Lol yeah
@@TheRealHelvetica i mean minecraft is so open for new stuff, it was from the start obvious the options are limitless. And as proven. Tons of new blocks been added over the years
Seems normal to me... I worked in Industrial Hygiene and we had signs for "Warning: Dihydrogen Monoxide" at all our water sources....
Fun fact: the first person to postulate that the other stars are heavenly objects like the Sun, rather than just shiny dots fixed on the heavens was Aristarchus of Samos (3rd century BC). He was also the first to propose the heliocentric model, but his peers mostly rejected the idea because they posited that if the Earth revolved around the Sun, the background stars whould change positions (parallax). Aristarchus' counterargument was that they were too bloody far away for a measurable effect on parallax to be observed. Since you need a telescope to observe a parallax angle, he was right. He was also the first to try and measure the distance to the Moon and the size of the Moon (with results very close to their actual values), using the newly calculated circumference of the Earth, which Eratosthenes measured just a couple of years prior. He then used those measurements to try and find the distance to the Sun and its size. It turns out though that it's impossible to do that measurement with the naked eye, and so he calculated the Sun to be just 20 times bigger than the Moon and 20 times farther away. In reality it's more like 400 times as distant and 400 times as big as the Moon.
That's more than one fact.
@@ratamacue0320 Hmm... ok. Fun blabbering. No that's an oxymoron. Just blabber I guess, then. :)
@@hellegennes fun facts. Plural. 😋
Actually it was some unknown to history woman in Greece.
the sun is WAY bigger than 400 times the moon.
"They're fireflies! Fireflies that, uh... got stuck up on that big bluish-black thing."
"Oh, gee. I always thought they were balls of gas burning billions of miles away."
"Pumbaa, with you, everything's gas."
In a way, he’s right, since solids and liquids are just thermally compressed gas, and plasma is thermally heated gas (don’t @ me with the many other states of matter, those don’t exist in great quantities in nature)
@@DiracComb.7585 I think that was the point lol
He got burning wrong
@@DiracComb.7585 there are a lot of neutron stars and while dwarfs out there and they are not one of the four main phases of matter
James Benton Ticer
Isn’t that why he said don’t @ him?
This man is a hero: wearing a Minecraft periodic table shirt while referencing the silmarillion and segwaying into stellar physics.
That's exactly the combination why I'm here ngl
Imagine being a stellar core photon, travelling for ten thousand years to the surface of the star, only to be halted at the last possible instant by an unfortunately placed atom.
Of course, if you really were a photon, you wouldn’t notice those ten thousand years passing you by, so I guess it’s not as devastating as it sounds to us time-locked entities.
Edit: spelling
The story of the life of my sperm. Except it's not an unfortunately placed atom at the end, but some latex. :-)
time doesn't actually pass for a photon the trip would be over instantly
Alex jones did you not see my second paragraph?
Photons are just trying to escape their families :P
true, though due to their speed, if we take general relativity in the limit, it seems photons would experience neither distance nor time. The life of the universe, from their perspective, would be over in an instant.
Cecilia Payne
Annie Jump Cannon
Henrietta Swan Leavitt
Lisa Meitner
Rosalind Franklin
And many more. Thank you.
You deserved more.
10:32 I really thought this was the time you say "Space Time". You really got me off guard with this one.
Lol me too
Same here
Gotta love the Silmarillion version, tho
Matt had me at 0:10.
3:10 to Yuma
Just made the video for me. Love it
A fruit carried by a hot goddess?
Bruh 🤣
Kudos for emphasizing contributions from women in physics who have historically gone under-acknowledged.
Playing the woman card I see
@@DrJams Playing the "lets give some respect to the very few women who made significant contributions to science despite society doing everything in its power to hinder diminish and ridicule them at every turn just for having a vagina" card, actually
I had never heard of her or the indian guy that published the ionization stuff. Really cool.
A photon checks into a hotel. The bellhop asks, “Can I help you with your luggage?” The photon replies, “I don’t have any. I’m traveling light!”
get out
Good one, dad.
Ffs you can see yourself out now
Of course, they can stay where they want for free, if you're a photon you're never charged.
@@TheGuruStud the door is over there.
Thank you for constantly going back to point out Professor Payne's importance. There are a lot of women glossed over during that time period. It's a shame we don't know her more. But you do a great job of highlighting her this whole video.
Fun fact:
Helium was discovered on the sun before it was discovered on Earth.
At least end your statement with "which is why it was called helium, because helios means sun". ^^
@@MasterChakra7, yes, that's a fun fact. Even more fascinating are the things that have been found in Uranus, though.
@@LordSplittawig ah yes, lots of gasses are measured from Uranus~
Yes that was a fart joke
I feel sorry for the guy or gal that went there and discovered it.
It’s absolutely astounding the progress we have made in the past 100 years in understanding... everything. We tend to think of a hundred years as a long time by human time scales but these days by modern life spans it’s only about a decade longer than a 1st world “long” life span. And by historical measures it’s a drop in the bucket. Thousands of years passed with only small advancements in our collective understanding of the universe, the world around us, and ourselves. Then in the span of 100 years or so we seem to have witnessed an exponential explosion in our understanding of everything.
Yay, a video about spectroscopy! This is exactly the sort of research I've been doing. If anyone's interested, I've got a video on my channel about a project I did over the spring to analyze the absorption/emission spectrum of Fe II - a particularly useful ion for determining the compositions of stars due to its dense spectrum. I'll have another video coming up soon(-ish) for some software I've written to enable researchers anywhere to precisely study NIST's archive atomic spectrum photoplates (once the archive has been scanned and is available online). Come and check out what atomic spectroscopy research is like firsthand! :D
I appreciate the time taken to share such important (and sadly lesser known) history of women in STEM! I also love the Minecraft shirt!
These are such great videos to deeper understanding of our universe! Thanks for taking the time to share your knowledge with everyone! :)
Thanks for posting this. It's a great example of how scientific progress is NOT an easy path on which any brilliant guy (male of female) walks straight towards fame, by simply having just a good idea and publishing it. On the contrary, it's often a very tricky, difficult and often tortuous path, a path full of obstacles like geographical origin, race, sex and conservatism. The first women who dared to follow the academic/scientific career about one century ago were just amazing, because for them everything was 10 times more difficult than for men, yet they gave amazing contributions to science, our modern society and our understanding of Nature and the universe. Because of this, I have a huge respect for figures such as Marie Curie, Emmy Noether, Vera Rubin and Cecilia Payne. They are true examples of what passion, dedication and hard work can allow ANY human being to achieve.
A Elbereth Gilthoniel!
silivren penna miriel
I used to work for Target card services in a call center, great time space and time. Good Target for sponsoring this kind of quality content.
The thing I don't understand about absorption lines is this: if the photon is absorbed by an atom by means of one of its electrons being bumped up to a higher energy level... won't a photon of exactly the same wavelength be re-emitted when the electron goes back down to its base energy level? Even if you say that the photon would be emitted in a (different) random direction, wouldn't that be offset by some other similar atom elsewhere in the star re-emitting its own randomly-directed photon in the direction of the original photon?
The emitted photon will then be absorbed by another atom.
The excited state often has several routes back to the ground state emitting a few photons of lower energy along the way (jumping to states with intermediate energy).
Think an aspect of that is also discussed at around 7:30
Actually, the photons emitted vary in wavelength on a bell curve depending on the temperature of the atom. This is the blackbody radiation effect and provides the vast majority of the source photons for which we can see the absorption lines.
@Toughen Up, Fluffy @FlashGeiger But shouldn't the situation be symmetrical? That is, if one atom can absorb a photon with energy A and then re-emit photons at levels B, C and D (where B + C + D = A), then shouldn't there be other atoms that absorb photons with energies B, C and D and re-emit one with energy A?
First time I'm seeing Target as a sponsor on TH-cam. I think Raid has started a trend.
Well to be technical, they sponsor PBS, which is not too unusual for large companies. Thanks, Target!
Hearing an Australian talk about "all 50 states" is... weird. I know everyone knows the meaning, certainly the people being advertised do anyway, it just feels weirdly disconnected.
@@KurtRichterCISSP Good point. He did say thanks for sponsoring PBS so maybe it was a deal to sponsor all of their channels or something. Either way, good on them. PBS has a lot of good educational content. Been watching their stuff since I was a kid. Or perhaps less of a kid depending on your view of late 20s. lol.
How topical, I'm currently in the middle of reading The Glass Universe, about the Harvard Observatory cataloging of hundreds of thousands of stars and Cecelia Payne has come up already.
Women are awesome! Always seem to get the short end of the recognition stick so love seeing them getting a good shout out! Great video as always, please keep ‘em coming!
I've seen the spectroscopy for Hydrogen so much I died a little on the inside when I recognized them on the Sun's spectrum.
You are just getting started...
Over the last year or so, I've been watching every episode of PBS Space Time in chronological order, and as of this video my much-more-knowledgeable self has finally caught up to the present day. What am I going to watch while drinking my morning coffee on non-workdays now?
A Silmarillion reference in my Space Time? *Happy Noises*
His shirt has upped my respect for this man tenfold
"Stars went from being utterly mysterious, to one of the best understood denizens..."
Me: oooohhh we're at the end of the video he's gonna say it
"... Of the universe"
lolllllll exact same response here
Me too.
Didnt even notice
I just referred this to several people because I failed to explain it. Your work is very well done and very important. The way you give credit the people that did the work is also great. But the explanation changes lives. It does.
Thank you, Cecilia!!
Wait, it's not made from cake???
Unfortunately it’s not
No but some are covered with icing
Hold on here, if the stars ain't made from cake, does this mean that the moon isn't made of Wensleydale cheese?
Tell me Wallace and Grommet were telling the truth, no?
@@JamesCairney The moon is a giant Mimolette.
"Never has been."
This is my favorite episode in a while. Not because there was anything wrong or bad about previous ones, but because this one was quick and to the point, rather easily understood, and celebrated the history/discovery of a brilliant woman in the field of physics, discussed too little. Not that I don't love the long format videos too, but this one just stood out to me. Was perfect over a lunch break.
Loved that Silmarillion reference
I love this video. Thank you. Representing women in science 🤗💫💜
Target of all people? Might need to stop buy and grab a few bed sheets... Thanks Target for supporting Space Time!
Wait - because this would be a great piece of trivia - we had Einstein’s Theory of Relativity before we even knew what stars are?
yes
Before we knew what they were made of*
Kind of a different thing
A light of the two trees of valinor reference...luv it!!!
I’m currently working on my bachelors in Astrophysics and about six months away from graduating and these videos are priceless for someone like me.
Woooww that's cool. Do you mind if I ask what courses u take for an astrophysics degree? (mainly I want to know what astronomy courses you take)
@@angelathomas6773 For astronomy I took a course called Galaxies and Cosmology, Planetary Science and a course called Stars which were all very interesting. I’m currently taking Quantum Mechanics and a course called Astrophysical Process. I will graduate in June.
@@gordonsimon5784 thank you! And congrats u're almost done :)! And good luck to u!
@@gordonsimon5784 tip of the day, go back to 1970 and read Hannes Alfvén's nobel lecture (downloadable from nobel website)
i enjoyed reading it, maybe you will to..
also it's noisy audio but the content is worth it, video on youtube called "Unzicker's real physics talks: Wolfgang Kundt, do black holes exist?"
what can i say i like thought provoking and controversial physics and so i wish you good luck in the field of astronomy!
Thank you for using more animations in this video. It really makes it better and easier to watch
Completely random fact:
Since the moment Pluto was discovered and until the moment when it lost its status of a planet, this celestial body has not completed a single full revolution around the Sun.
-SciFacts
To be precise it only completed 30% of one orbit.
I haven't done that either tbh
I only move in time but not in space and honestly I have no idea how I have cell service out here in the void.
Ireallylikeeggs
I like eggs too
Kinda sad it didnt even get to see all of the solar system yet before losing its planetary status
If this was any other channel, I'd look at the title of this video and be like "well obviously know that"
But it's PBSST, so bring on 12 minutes of content that's over my head :)
Loved the t-shirt!
That shirt is fantastic!!!
love the way he explained this.. i actually got it, me and my feeble mind
*THANK YOU SO ENDLESSLY MUCH* for picking up my comment _& making an entire episode about it!!!_ *
1:48 Sir Arthur Eddington looks like Steve Carell.
Nice.
Perhaps this channel isn't the most appropriate, but I would really love to see more "history of science" videos. I know SciShow has done a few like that, but absolutely love looking at how our understanding of various phenomena has evolved generally from wonder and myth, to the various theories that prove themselves wrong or on the right track, to where we are today. Not to say we have all the answers today, to be fair.
That's one reason why I like Dr. Becky. She has a series called "Great Debates in Physics". She tells the historical advances in the state of the art, right down to the individuals who had disagreements.
Normal people: here for actual content
Me: what shirt is my boy dr o’dowd wearing today
Love the Pink Floyd reference, one of my favorite bands!
There needs to be a posthumous “Nobel” award for people like her who were overlooked while they were alive by the Nobel committee.
I’m thinking not only of Cecilia Payne, but also Rosalind Franklin (DNA X-ray crystallography) and Jocelyn Bell (discovered pulsars).
Oh heck, throw in people like John Bell (discovered Bell’s Inequalities, used to prove that local hidden variable theories don’t work) too.
That award doesn't mean much outside of science. And science has other things like impact factors to measure the contributions
Franklin was not overlooked; she died before anyone received a prize for the structure of DNA.
Thank you for a giving Cecilia fantastic air time 🥰🥰
Target's been around since 1962? I gotta practice more patience in establishing my business.
Thanks for the Bio, truly deserved
A while ago, I asked for help on this channel with figuring out where some planets and local stars would be in the year 3021. Well, I didn't get any useful help then, but... I did figure it out on my own, and it turns out that unless we discover a fairly large Trans-Neptunian or Oort Cloud object, the best place to launch a trip to Alpha Centauri from the Sol system (by relative distance) is....
....
....
Neptune!!
@@randy2811 so much to unpack in that criticism.
1) Yes, the sun is a gravity well, but...just like the planets, you can't really "escape" from it. The farther you go, the less impact it will have, which is actually *why* you want to start a trip at, say, Neptune instead of Earth.
2) You have to start from survivable physical object. You could no more start in the vacuum if deep space than you could the surface of Sol, so a planetary body or other large body, like TNO or KBO.
3) I think you must be missing something in the original question
4) Turns out that in 3021, Neptune will be the farthest large survivable object on a nearly direct line between Sol and Alpha Centauri, and it's on the correct side of our star. Other bodies are farther away from Sol, but on the wrong side (either 90 degrees off or on the back side). Other, other bodies are on the correct side, but way too close. So, without another TNO or KBO that's large enough, Neptune makes the most sense for the shipyard/launching point. At least, it does in 3021. An eighth of the way through its orbital period, that might change, but I didn't do the math for that.
I would assume it’s by minimizing energy rather than distance, but it seems likely starting farther out (if you count that as free) is better. This is complicated because you can boost your velocity by up to double each large object you can slingshot off of.
@@burtosis Minimizing distance (or rather maximizing distance from Sol) does minimize energy needs. It also reduces travel time.
Since this is a work of semi-hard science fiction, the slingshot effects, which would be incredibly useful - if not absolutely necessary - in the real world, are considered negligible for the realism if the story. But, good catch.
Periodic table of Minecraft lmao. Love that shirt.
So.... What happened to "The great courses plus" intro? Had gotten so used to that 😂
All day I was interested in what stars are made of. But after listening to this man speak I don't even care anymore. You nerds have it under control. Good luck.
Wow, good timing.
I have a much greater respect for Matt after seeing him on Neil DeGrasse Tyson's show, with Neil stepping all over Matt's answers and comments and CONSTANTLY interrupting him. It took my respect for Neil down a notch and elevated my respect for Matt. Why? Not just because it's rude and socially cringey what Neil did, but the REASON why he did it: Neil felt threatened by Matt.
Very rarely does Neil have people on his program that can actually take him to the cleaners with their level of understanding and communication. And Neil obviously felt threatened that Matt would (huh) *eclipse* him with his knowledge, youth and good looks. Childish, I know, but we are all still cavepeople in those limbic folds of our brain.
Good on you, Matt! You're a total hero of mine! Uh, for your BRAIN, not your looks...
Yesss finally! I’ve been waiting for a new upload 😅
The Indian physicist Mr. Saha should also be credited for the discovery as it was his technique and his finding first.
Citation?
@3:38 I have an odd desire to listen to Pink Floyd for some reason.
This video was very illuminating
Target?! Moving on up on the sponsorship!
Wow, it's one of the most comprehensible videos on channel! Good job, PBS Space Time)
You may not have heard of
Cecilia Payne
And that's a shame...
Is it me or anyone else found it rhyming?
Target picked a great episode to jump on
I thought the first thing that you learned in Astronomy was that everything was spherical... ;p
Awesome motion videography
This work also helped us to understand what elements can be made from different classifications of stars. That is how we know the heaviest element our sun will produce is iron.
The heaviest element which can be produced by nuclear fusion in a star is Iron. Anything heavier is produced in a supernova.
AFAIK our sun won't make it to iron. It takes a Supernova capable star for that.
Love the Minecraft shirt and the Tolkien reference!
Great informative/accessible video,as always. I really enjoy hearing how we came to know what we now know.
When is the new challenge question coming?
and me.
Thank you Target!
How you know a TH-cam channel has made it to mainstream success: when they get normal ads like Bounty, Colgate, and Target vs. rAiD sHAdoW LeGeNdS, skillshare, etc.
They're a pretty safe bet
Eh, I would disagree. You can tell when a channel doesn't talk about controversial material by those metrics, but I would call plenty of channels without those advertisers successful, they just require funding from patreon. Contrapoints is a great example of this!
Wow, such a clear explanation of spectroscopy! Amazing job!
Last time I was this early, the photons were still coupled
Quirky space joke 🤪
Lol nice
You've never been really, stop bragging
Nice shirt, Matt! 👍
SUCH an important video. Much of this is still over my head, but Im so grateful for it.
Yeah, those "basics" are sooo important to building up the whole picture. They deserve to be talked about more frequently.
@@NeinStein Spot on. ;) This knowledge could save poor lost humanity.
Question: What is the mechanism by which mass/energy curves spacetime? We have the observation that it DOES, and equations that very accurately predict the degree of curvature, but I've never heard a hypothesis, or even a "best guess", concerning HOW curvature occurs. I realize this probably comes down to, or runs into, the QM/Relativity incompatibility wall, but hypothetically, "best guessedly"; what is doing what to what?
Mark Rosenthal should receive a standard Type Ia-O hypergiant for his donation.
Scheduled for delivery in a few billion years, naturally.
Great video, very educational stuff. I believe the title you bestowed on Mark Rosenthal at the end, "The stariest star of all", is perhaps the most glorious title ever bestowed on anyone! But I also believe that this title should be shared posthumously by Cecilia Payne, for shining so much light on the nature of stars. ✨
I always wondered how we knew how the spectrum of absorption lines reflects the entirety of a stars' composition and not only the outer layers?
I wondered that as well.
All photons are made in the core, and if they bumped into other element these colors should be absorbed as well.
@horizontal: In other words, how do we know the outer layers do not have a radically different composition then the sun's inner layers?
Three big reasons, 1) temperature suggest the entire sun is a plasma gas, 2) gasses readily diffuse through each other, and 3) the energy levels combined with convection currents suggest very good mixing.
@@bananaforscale1283 Light bouncing off free electrons do give rise to elemental spectral absorption lines. Only with light exciting electrons orbiting a nucleus do we see spectral absorption lines.
Because the core is undergoing fusion and the inner layers are ionized, so the conditions don't exist for stable atoms and bonding. It's all a big soup of charges.
Great video....Thanks a lot for your teaching....
But in equilibrium the energy of an excited atom has to be released eventually, by the same energy transition (pretty sure this is where my assumption goes wrong), releasing a same-frequency photon. So why would there be an absorption band?
Bump
Emission doesn't always happen, since the higher energy level could just be in equilibrium with heat.
Emission lines are indeed the same, but they're not in the same direction and so are diffuse. So now you might ask why emission from other parts of the sun with our direction as the "random direction" don't just cancel out the absorption. Valid question, but the random direction includes back at the center of the sun (which can radiate back at any frequency), so overall the energy directed at us decreases with increasing concentration of that element
That said, the exact nature of sun has enough unknowns that conspiracy theorists use it as a hole to posit new thermal emission theories (i.e. replacing stefan's law)
Perhaps it's worth an episode to debunk that one, you basically have to work through the math for a while until you find the inconsistency with observation
The emitted photons are absorbed by other atoms.
Thanks Cecilia, very cool!
OMG Two weeks ago i adopted an tiny female orange tabby kitten, and I named her after CECELIA PAYNE (Cece for short). No joke, wtf are the chances???
Oh wow, you know a channel has seriously 'made it' when a corporation like Target sponsors their video!! Daaang, way to go Space Time!
You say the energy of a photon has to be exactly right to be absorbed by an electron, but how precise does it really have to be? The frequency spectrum is continuous, so shouldn't the odds be zero of a photon having any exact frequency?
The frequency spectrum comes in quantums actually. All possible energy states in Universe are multiples of Planck energy.
Absorption lines are not infinitely thin (if they were, you couldn't see them) due to quantum and other effects. See www-star.st-and.ac.uk/~kw25/teaching/nebulae/lecture08_linewidths.pdf
the other comment is correct. E=hf and since h is a constant defined variable, the energy can only come in discreet packets. For example you could have a photon of energy 1 and a photon of energy 2, but not a photon of energy 1.5
@@linksfood so what happens when a photon gets redshifted or blueshifted? Does that only increase or decrease energy in steps, too?
@@michaelsommers2356 this is really useful, thanks!
I love Matts shirt!
Can we just appreciate how her PhD was about discovering something unknown to humanity at that time. A big chunk of today's PhDs be like 1+1=2.
most times phds are about something very specific. as far as we can tell, there no big mysteries that one doctor can solve alone. Sure, we have quantum gravity, but it is so complicated that you can't do much work alone
PhDs today be like “Elucidating the molecular mechanisms of conformational dynamics of RNA-binding proteins in complex with viral RNA in vitro using electron paramagnetic resonance.”
Her PhD thesis is considered by many to be the most significant in the history of astronomy.
Thank you for being the star scientist (😏) of 20th century astronomy, Cecilia Payne! If I ever have children, I'll make sure to tell them about your contribution :)
Wow, less than 50 comments :D I want that T-shirt!!!
Beautiful story
There are no such things in Tolkien as "the trees of Elanor". Elanor was a small yellow flower seen in Lorien, after which Sam named his eldest daughter. You're no doubt thinking of the Two Trees that gave light to Valinor before Melkor poisoned them. So maybe you meant to say Valinor, not Elanor. "Varda Elbereth" was pretty much never said. Eldar in Middle-earth addressed Varda in the Sindarin language as Elbereth, meaning "Star-queen". Varda is how she is known in Aman, by speakers of Quenya.
And why was there a graphic of the western doors of Moria behind you when you said that?
Nerd. >.
@@itcamefromthedeep Damn right.
here come the LOTR nerds
@@booketoiles1600 What an original comment that someone else didn't make 15 hours before you did.
You had me at Varda Elbereth.
It's weird to see Target ad on PBS Space Time..
You've main the most nerdy awesome TH-cam intro ever....reallly....I am in awe.... :)
👌👽
A correction!!
At 7:05, it's Meghnad Saha not Meghdad Saha!!
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