We Can't Measure* Distance In Outer Space!
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- čas přidán 6. 05. 2024
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We can't measure the distance to astronomical objects directly, so we have to be creative. That's why we need the cosmic distance ladder. It's a serious of techniques we use to calculate astronomical distances indirectly.
Nick Lucid - Host, Writer, Editor, Animator
Em Lucid - Producer
Nora Bailey - Researcher, Fact-Checker
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SOURCES
Radar Ranging:
doi.org/10.1016/0019-1035(73)...
ilrs.gsfc.nasa.gov/science/sc...
Parallax:
doi.org/10.1167/9.1.10
sci.esa.int/web/gaia/-/53278-...
www.esa.int/Science_Explorati....
doi.org/10.3847/1538-3881/aacb21
Cepheid Variables:
astro.wku.edu/labs/m100/PLrela...
www.atnf.csiro.au/outreach/ed...
doi.org/10.17226/9585
doi.org/10.1086/126870
Type 1a Supernovas:
arxiv.org/abs/0705.0726
doi.org/10.1086/186970
doi.org/10.1146/annurev.aa.30...
arxiv.org/abs/1608.04192
Cosmological:
astro.ucla.edu/~wright/CosmoC...
arxiv.org/abs/astro-ph/9905116
doi.org/10.1093/astrogeo/aty268
iopscience.iop.org/article/10...
arxiv.org/abs/2208.13642
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IMAGE/VIDEO CREDITS
Apollo Retrorefector:
commons.wikimedia.org/wiki/Fi...
www.nasa.gov/image-article/re...
Deep Field Flythrough:
svs.gsfc.nasa.gov/31035/
Gaia Animation:
www.esa.int/ESA_Multimedia/Vi...
Milky Way (Artist Rendition):
images.nasa.gov/details/PIA10748
Type 1a Supernova:
svs.gsfc.nasa.gov/13852
commons.wikimedia.org/wiki/Fi...
Barred Spiral Galaxy (NGC 1300):
images.nasa.gov/details/GSFC_...
Redshift Cube:
svs.gsfc.nasa.gov/14105/
Redshift Zoom:
svs.gsfc.nasa.gov/14301/
Galaxy GLASS-z12:
commons.wikimedia.org/wiki/Fi...
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TIME CODES
00:00 Cold Open
00:22 Introduction
02:05 Radar Ranging
04:17 Inverse Square Law
04:57 Stellar Parallax
08:46 Standard Candles
10:58 Cepheid Variable Stars
12:58 Type 1a Supernovas
15:15 Cosmological Redshift
18:37 Summary
19:44 Nebula Ad
20:52 Outro
21:05 Featured Comment
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Light trying to get to us as space expands is like swimming against the current as you try to get to an island.
You two work well together :)
Great theme.
Thanks for the reminder, Nick. I’ve been subscribed to Nebula for a while, so I added your channel just now and am looking forward to your next video right after I finish the latest one from Extra History. 😊
Note about the Correction: This is due to the stellar magnitude of an object being greater when the brightness is lower, which is counterintuitive until you realize what was meant by "magnitude" when its use for stars was invented. The number isn't the amount, it's the rank.
"Stars of the first magnitude" meant the brightest ones; "Stars of the second magnitude" meant the next brightest ones; etc.
Once instruments came along that could measure amounts of light, we could make stellar magnitudes into numbers with fractions, not just integers.
The format of this video is perfect. You get discussion and reaction and interplay of ideas. Splendidly done, both of you!
Fred
"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is."
I once heard it was like.. literally physically impossible for humans to even be capable of thinking of both *the infinite* and literal *nothingness.*
I have no proofs or references for this statement.
RIP Douglas Adams. Went far too young.
Like minecraft innit
I mean, you may think it's a long walk down the street to the chemist's, but that's peanuts compared to space.
Not bad for a Golgafrincham B Ark descendant. o7
This was illuminating! Thanks!
Thanks Mehdi!!
Hi Medhi and Nick , let's you guys collab about the Peltier cooler, how it works at quantum level? @ElectroBOOM @ScienceAsylum
Especially the standard candles 😂
Many candela of illumination!
Pun intended...😆
It's so awesome to have a partner who likes listening to you nerd out and actually takes an interest in the things you love.
Over half a million subs? He pays her.
@@47f0 I'm sorry that your marriage is so empty that you think I have to pay my wife to be a quality partner 😢
@@ScienceAsylum - Nah. I just think you're lucky enough to be married to someone smart enough to get paid.
@@47f0dude, why are you acting like blud can’t find love? Quit being a hater.
@@jayde4872 - My wife loves me. When my back was blown she tied my shoes. When she helps me on one of my accounts, she gets paid. It's not that freaking deep.
I'm always surprised about how big the universe is. "It is so far that distance doesn't make sense anymore" is mind blowing
Thats what Douglass adams was trying to say.
You might be more surprised.
For context, let's say if the Earth was as big as a water molecule, then the observable universe was as wide as the Pacific Ocean... times 1000.
I don't really like that description "so far away it doesn't make sense". It's still the same concept of distance we always use, it's just that at after some point we can't reliably measure it anymore and we have to use other metrics that approximate what we want to know, which is the distance itself. That's what redshift is for. You can say it's hard to imagine things being that far away, but it doesn't stop making sense. M said it best, it's "far far away".
@@mrgalaxy396well, yes _and_ no. Yes, of course we can approximate distances in space, and those distances do have at least some meaning to them. But then we can measure the velocities of certain objects also, but it's still not possible to say that some object has an _absolute_ velocity, to state that it is travelling at a _defined_ speed. This is because all _relative_ speeds are, as their title suggests, subjective in nature. And as such they hold no objective meaning.
All velocities are relative. Ergo, talking about absolute velocities is meaningless.
And so it is with distances. Beyond a certain point (determined by an observers light cone - as defined within special relativity), talking about absolute distances simply ceases to become meaningful. Or, in other words, distances become meaningless. As stated in the video, we can determine the redshift of light that has travelled to us from the very early universe, but this is a _relative_ measurement. It is observer dependent. For the light itself _no time whatsoever_ has passed since it began it's journey. _We_ see the photons redshifted, however, the photons do not see _themselves_ redshifted. Redshift is a relative phenomena. And as all relative measurements are subjective, rather than objective, in nature, measuring relative distances is ultimately as meaningless as measuring relative velocities.
I remember feeling slightly sick when I first learned this. It was as though the floor had just dropped away... was _nothing_ really... well, real, I wondered? It's one of those cases where the more you know, the more you know you don't know, I guess. Sorry. Anyway, I'd still prefer to know that I don't know, rather than to remain ignorant even of my ignorance.
As Aristotle apparently said shortly before he died,
*"All I know is that I know nothing."*
Anyway, have a great day!
@@mrgalaxy396 The suggestion that distance in the conventional sense no longer make sense, is that when light take so long time to travel from that star to Earth, we can no longer form a meaningful objective reference frame to put the Earth and that star in the same reference frame. We don't share the same clock. Our times don't tick together in sync.
Your videos with you and your wife, the banter you guys have and the questions she asks, really are the highlight of my day. You guys are great together.
Thanks 🤓
She is nice!!!!
This is just a fantastic way to learn, it's like hanging out with the friends who are smarter than you.
This video shows once again that having a co-host or guest who is really smart, genuinely curious and generally knowledgeable but, due to their specialization in an entirely different field, has little to no idea about the topic at hand is always a huge plus for educational content. 😊
I absolutely love how pragmatic her observations are. Like “stars existed back then why didn’t they name it standard stars?” That’s such a good point. 😂
I absolutely LOVE these discussions! The questions she asks as a non-expert in your field really makes these videos feel more 'interactive' considering she is also acting as a sort of 'stand-in' for us viewers in 'real time'. I don't watch podcasts generally, but I would *sooo* watch one of you two as you guys discuss and explore each other's specialties/fields of expertise!
oo you're totally right! Well said :)
very well put
I think I love these videos because you are kindly explaining a complex piece of your mind with someone you love who hasn't been exposed to the knowledge you gained to build the understanding in your mind. It's unique, wholesome, and educational.
This was very fun. I really like these conversations with Ms. Science Asylum.
This channel is amazing. Nick is batting 1.000 on teaching me concepts in unique ways that provide huge insight other educators seem to take for granted. Love it!
Glad you enjoyed it! 🤓
I wonder if 1 other important part that I felt was only glossed over at the end, would help you. Namely, that none of these things is measuring a distance, not even RADAR. But even at the Type 1a scale, distances can be interpretation dependent, and each of the various methods has there own uncertainties. So, stating the measured value and while using what method is really the best way to talk about any of these kinds of things, and any kind of local distance, like kilometers or whatnot, is a simplification, tho useful in some contexts.
This realization that nothing is a distance outside of very nearby astronomical objects was very eye opening to me. I think this was a Vsauce shorts video.
I love episodes where you explain things to your wife. Gives such a great vibe. Emily reacts with the things I would have wanted to ask. Much love to you both.
I really like this format, the "on the shoulders of giants" progressions, where you start where things makes intuitive sense and take the baby steps to reach the stuff that feels absurd.
Erathostenes be like :
"Young man, I kind of started all this astronomical measuring stuff more than 2000 years ago! Measuring Earth itself with shadows of a stick, and clever assumptions! A century you say... This is outrageous!" 😄
1st time viewer on the channel, very pleasant discussion, and thank you for the refresh on the topic 😊
I am an actor, and I was amazed at your presentation of distances. You have a great format of discussion. I mean, I couldn’t put my phone down!
I hope your chemistry is the same in real life, you two are lovely.
If soulmates exist, her and I are it.
I wanted Nick to tell her about the ant on the elastic, and how it gets to the end. When they were talking about light trying to get to earth but space was expanding.
Somehow I never encountered an explanation for jumping from paralax to cepheids and supernovae, this is the most helpful. Keep making those videos, they're the best at filling those gaps in a public/popular understanding of physics and astronomy
it's also worth noting that due to the ladder of calibration there is the potential for stacking tolerance issues (like at which decimal point you stop at in a calculation of each rung on the ladder) that could potentially invalidate every "measurement".
A cool nugget on optical parallax of human eyes, which I've actually done, as a kid:
If you get or make a periscope, you can use it to amplify your binocular vision by increasing your effective interpupillary distance. Just hold the periscope horizontally, looking into it with one eye while the viewing opening extends out away from the other eye. With both eyes open, you get enhanced depth perception!
Thanks for another cool vid!
Fred
Interesting. How about using two periscopes, one for each eye 👁️😎👁️
@@david94549 Much harder to keep the two images coalesced, and so, not worth it.
Unless you go to more trouble to make the instrument into a single large piece, which will then need 4 mirrors altogether, instead of just 2.
But you can get the same parallactic baseline either way, so long as the overall horizontal distance is the same, between the 2 "viewing apertures."
Easier just to get a pre-made periscope and use it on one side.
@@ffggddss yeah I was tired when I commented this last night, now I realise you can just use a longer periscope to further increase the depth perception
@@david94549 Don't fret that; it was a perfectly reasonable suggestion, one that had occurred to me at the time, but that I just didn't have the materials or patience to implement. And I think that if you wanted to maximize the parallax amplification, that would be the way to do it. It would just be more trouble to build. I guess it would look somewhat like binoculars - at the eyepiece end, at least. And one really rigid bracket or beam to mount the 4 mirrors on.
Oh my God that's horrible, like having an eye on a stalk ffs I have to try it
I knew that the effect of parallax decreases for things farther away, but I never made the connection that depth perception also decreases. This channel never fails to give me new connections to things I already knew, and I love it very much.
Your attention to detail is remarkable. From the visuals to the audio quality, everything is top-notch. Your commitment to delivering a polished product really sets you apart. Kudos on the excellent production!
Thanks! I work really hard on these.
Yay! An episode with M! Love the dynamic you two have and great way to deliver information, learned a lot this episode, haven't heard of half of the ways to measure before. Thanks for the lesson as always !
Glad you enjoyed it!
I'm glad you explained each layer well enough for most people to understand. They all sound a lot simpler, and still somehow work!
It's one of the benefits of having my wife there 👍. My training is classroom teaching, where it's common to adjust in the moment based on immediate feedback. When I make a normal-style video, I have to guess and hope, which doesn't always work out.
@@ScienceAsylum Guess and hope has resulted in some of the best science education on here! ❤
@@geemcd Thanks! My experience definitely makes me a better guesser. To be fair though, I do miss the mark _occasionally._
I wish i had a science teacher like you back in the days when I graduated from high school. You have an unique way to keep up the listeners attention and also explain complicated things very easy and understandable.
"Starts to siphon off mass from their their companion", "Which one", "The white Dwarf".
...I love both y'all even harder.
My father was a tech at Auther D. Little in Cambridge, MA in the 60s and worked on the moon reflector. It was a panel array of aligned, individual glass mirrors. As I recall, each individual mirror had three reflector planes that were mutually perpendicular so that any incident light pulse will be reflected back at the same angle like a radar corner reflector. He had a single imperfect mirror which he brought home to show my brothers and I. I believe the refector array is still working today and is even used by amateur astronomers to measure the distance themselves using laser pulse generator/detectors.
I love how the complexity level suddenly drops down to our casual approach of measuring distances.
It is so great to be reminded how intelligent humans are, even back when we were using the parallax method for measuring. Your explanation of how we are now able to obtain distances beyond our galaxy cluster was enlightening! Thank you!
On another note, I’m going to start using the standard redshift distance numbers to let my friends know when I might arrive when making plans 😂😂🤓
Watching all the way from Nairobi Kenya 🇰🇪 … amazing work you guys are doing! Keep up the good work!
For those curious how we calculated these distances before radar, there were a number of methods. For example, by observing the terminator on a quarter moon, you can determine the relative size of the sun, earth, and moon. This is because at a half moon, the terminator is not exactly a straight line but a subtle arc. This method was used by Aristarchus over 3200 years ago, but the measurement is too difficult without a telescope. But even with an early telescope, it was possible to make accurate measurements. This can be combined with the angular sizes of the sun and moon (both at greatest and least extent) and the diameter of the earth to calculate the distances and sizes of the moon and sun and the shapes of the orbits.
(The diameter of the earth is easier to measure, and there are many ways. One simple way is to pace out a long north-south distance and then use celestial observation to determine the difference in latitude.)
Once we know the shape of our orbit around the sun, we can calculate the orbits of all the other planets. This was done by Tycho Brahe and by Galileo Galilei, but obviously they reached very different conclusions (with Brahe believing the sun orbited the earth). By the time of Newton, we already knew the basic shape and size of the solar system out to Saturn. Further confirmation came from measurements of the phases of Venus and Mercury, transits of Venus and Mercury, and eclipses.
But calculating the distance to stars was still difficult. Although the method of parallax was known since ancient times, astrologers had always known that this parallax was unobservable, seemingly zero. This was originally taken as evidence that the earth did not move and later as evidence that the stars were extremely distant. The inability to observe parallax even with the best telescopes meant astronomers could only place a lower bound on the distance to the nearest star.
But in 1725, James Bradley and Samuel Molyneux observed motions of γ Draconis and 35 Camelopardis that they thought might correspond to parallax. They were quickly able to model what motion should be expected of parallax, nutation, and other movements and found that this corresponded to none of them. In fact, the apparent motion was caused by the aberration of light: since light has a finite speed, an observer on earth sees the star as it was, not as it is, causing a slight discrepancy depending on whether the earth is moving toward or away from the star. This provided an accurate measurement of the speed of light and the distance to the sun, but not of the distance to the star.
Stellar parallax was not measured for real until the 1830s, when Friedrich Bessel calculated the distance to 61 Cygni. After that, numerous measurements were made with powerful telescopes, giving us absolute distances to many nearby stars. In the 200 years since, telescopes have improved, particularly by putting them in space. The space telescope Gaia has now measured the distances to over a billion stars, some tens of thousands of light years away, including all stars of magnitude 15 and brighter.
Your wife is great, hope to see her back! I also wanted to mention how well this format works for educational content. I don't know what you call it, in the movies its the _fish out of water_ character but more specifically I would call it the teacher/ pupil format. If there is one way that helps me understand complicated topics where I cannot readily ask a question myself, this is what works the best.
Well done! I’ve seen the distance ladder exclaimed a hundred times. Almost always some important detail is left out because the presenter instinctively thinks it’s obvious, but it’s only obvious if you already know it. This is one of the few times I’ve seen someone touching all the key points: how there is no way to measure directly and we need indirect methods. How each method has limits. How each method works. The _absolute importance_ of the range overlap between methods, so that we can calibrate each subsequent method by measuring the same-ish distance by both a shorter-range method we already trust, and the next longer-range method. The only nick-pick (no pun) I have is that you didn’t go into how we know about the cepheid variable period/luminosity relationship, which I think is a lot of fun.
Thanks for the high praise! Also, we did talk about everything in much more detail, but a lot got cut for time. I plan on doing a couple deeper dives: one on Cepheids and one on Type 1a 👍
One thing I couldn't follow was the explanation for the red shift. I would imagine that, like brightness, you would need to know the original frequency of the light that was emitted to calculate how much it had red shifted. Did they also have a standard candle for red shift?
It left out how the diameter of Earth's orbit around the sun is measured. (6:59)
@@aviecenna8579 you’re absolutely right. And we do have a standard candle for redshift because each chemical element emits precisely in the same exact colors, always and everywhere. This is actually trivial to do compared to cepheids variables. We take precise spectroscopic measurements; we see where the emission lines actually fall in the spectrum for these faraway objects, and we know where they are _supposed to_ fall (because “hydrogen always emits light like hydrogen does”), and so we literally calculate how much the observed spectrum needs to be shifted back towards the blue until it matches what is supposed to look like
@@brothermine2292 oh, you’re right. But I suspect that’s a whole video on its own
Why do I sit grinning at the monitor the whole time you two are chatting? This is such a fun format for going through topics. Thank you! Man, the point about the original distance being shorter than the distance the light travels completely blew my mind - had never thought of that! And that point about us already using time to describe distance ("20 minutes away") such a cool observation.
I believe the reflectors we put on the moon are retroreflectors, like the ones that come on an ordinary bicycle, but bigger. They are geometrically designed to reflect any type of light back to the exact direction it came from, so you don't need as much light to be able to see them.
The channel Technology Connections did a great video on retroreflectors.
You lost me at Cepheid variables
Some additional information is necessary. In particular, why the luminosity period is related to its absolute luminosity. Which physical phenomenon explains that?
@@j9dz2sf This was just a general overview. I plan on doing a couple deeper dives: one on Cepheids and one on Type 1a 👍
@@j9dz2sfit’s called the Leavitt Law. Basically, some awesome person Henrietta Leavitt was tasked with looking at light curves of these Cepheid variable stars and she noticed a relation between the period of the stars and the brightness
This one was completely new to me. The other steps before and after I was aware of. Although I thought the type 1a supernovae was the standard candle. Maybe I missed that part but the video made it like that the supernovae is already beyond the standard candle. But cepheid variable. Never heard that term before. Cool. At least now I have the whole laundry list of methods we know how to measure distance.
@@j9dz2sf Well, without explaining the mechanism underneath, we can still easily calculate based on anecdotal evidence.
We have many Cepheid Variables within the range of the Stellar Parallax. So by using the Stellar Parallax, we can calculate how far they are, and thus how bright they actually are. Using that, we can correlate between how fast they pulse and how bright they actually are. It's just lucky that from all the Cepheid Variables within the Stellar Parallax range that we measure this way, it shows these 2 factors do indeed correlate with each other, so this is proven.
Then, by measuring how fast the Cepheid Variables beyond the Stellar Parallax pulse, we can reverse calculate how bright they actually are, and by comparing it with how bright the stars appear to us, using the inverse-square law we can calculate how far they are from us.
I love this wife reacts series! I always learn so much from you guys :) And it's so cool to see how knowledgable you are Nick, totally unscripted, you just know so much!
Thanks Jade! Sometimes I feel trapped in my normal format. With these conversations, I get to let loose and nerd out.
One time I was going over my old trigonometry book, years after I took the class, just to keep things fresh in my mind.
I was staring up at the stars, wondering if trig could be used to calculate the distance to a star, knowing full well that the measuring distances would have to be very large to get any discernible angle.
Didn't realize it was a method that was actually used.
Anyway some police officers came up to me and asked if I knew anything about someone going around trying to break into garages in the area.
I had no idea, but the scene from Men In Black where Will Smith's character shoots the little girl because she's out with a physics book at night crossed my mind.
It was a weird experience.
Very strange
I knew (mostly) every think about the astronomical ladder, but I was delighted to listen to your explanation; very clear and very comprehensive 😍
These are my favorite episodes! You guys are great on camera together.
Always great to see you two talking, great educational video as always. ☕ Appreciate you Nick!
I couldn't wait to see/hear Nick bring up Cepheid variables! 😄Also, it's awesome to see Em tag team the outro! I love this format of one grilling the other on their chosen subject, and I think it'd be awesome to see Em nerding out about biology while Nick grills her on the chosen topic. 😉
I love moments when I learn something profound that changes my perception of nature. So the distance we measure light travelling wasn't the actual distance of the object when that light started its journey - because of expansion. Seems so obvious, but that had never occurred to me before. And the way we calculate distances was fascinating to learn. Thanks Nick for expanding my world yet again !
This video is abridged and concise version of a 2+ hr video. SO much content squeezed without any deviations.
Well Done Sir !!!
Thanks! 🤓
i love these explainer type videos with your wife. she is educated enough that you don't have to explain every little thing and you can focus more on the relevant information. keep it up!
9:36 I love how he starts talking thinking he’s going to argue then realizes he’s talking to his wife and knows better. Thank you Em, this made my night.
Really happy to have found this channel. And thank you for the Nebula recommendation! Knowing there's an online community that talks about the stuff I think about, and in the way I think about it is so cool. Thanks for making content!
Your videos have always been great and I'm really liking the casual discussion/explanation of these topics you and your wife have. It makes the highly complicated information more digestable and less "intimidating" for laymen like myself.👍👍
Glad you like them! 🤓
Nice to see you and your wife doing a video together. Great video!❤
Thanks 🤓
The thing about cosmological redshift models is that it usually assuming an expanding universe model, which (Occam’s razor) is not the simplest explanation. Many other things can cause light to lose energy and redshift such as dark glow plasma
I love this channel so much simply because I've watched you from your infancy and now to see how far you've come.. Just watching you I have such a proud grin on my face. I feel like a parent. Even though I've had no input in your success.
You're great. I'll leave it there.
The back and forth between you two make for my favorite shows.
Not sure I'm a fan of this scripted conversation format, although other formats would make the video unnecessarily longer
@@skan5728 These conversation videos are _not_ scripted.
Amazing video, as usual! Working from first principles to explain complex topics is always very satisfactory, and you've done it brilliantly.
Really nice video. Best description of the distance ladder I've ever come across. The collaboration with your better half was very effective! Thanks.
This could not have been better explained. Like being in the company of two very bright friendly people who care about knowledge and really want to share what they know or are discovering.
Husband and wife making measuring jokes. Immediate like
😆 We're such nerds.
@@ScienceAsylum beautiful nerds :)
M asks exactly the questions that I, as a non physicist, would ask. I love your chemistry! Keep up the excellent work!
Wow. You are probably the first science communicator I've heard that had stated so efficiently that the distance is the distance that the light had traveled.
Great video! I particularly liked the Cepheid variable section as I wasn't too familiar with how those worked. Neat to see how it "stacks" on top of stellar parallax.
Thanks! 🤓 I thought it was an important video to make.
You & Emily are awesome. Want to see more of Emily. I really ENJOY the science you teach, and the way you explain it makes it learn able and entertaining! Keep up the good work.
Thank you for doing this video.
"Suddenly" it all makes sense.
Now I can't both help but wonder why, and be "perturbed" about it, that this was never adequately explained in any of my astronomy courses, or in any books I've read. I guess I didn't read the right books.
You and Em saying Ahoy is the most stupid adorable thing. My wife and I watched it 3 times back to back just dying. You look like you can't help yourself but say it back, Nick, and I can respect that.
You two are awesome. Keep doin you.
This is an excellent format. Further your partner and you NAILED the questions AND answers each step of the way. I always thought when you're in the 50-100% of the size of the observable universe area in terms of distance just quote the fraction to the edge of the observable universe (or surface of last scattering or whatever). I know it's not linear but what you gunna do.
I love watching you two together. As much as I love you in front of your bookshelves. Seeing things like the Shadowrun books and gaining a little insight on you. Have you considered more videos of the two of you playing off each other? Maybe adding clones of your wife with your clones ;-). Great video.
Love the episodes with your wife! She has the right level of knowledge & intuition to clarify these concepts.
The issue of measuring distances in space becomes much worse when considering the problems from the perspective of Time... All of our measurements are based on the presumption that time is UNIFORM across the entire galaxy/universe and that the measure of 1 light second/day/year is the same on earth as it is across all of space (which isnt the case at all but we ignore that to get a "ballpark" estimate).
Light passing through a gas/plasma cloud for instance slows the propagation of light down by a significant factor related to the material light is traversing through (refractive index or ri). Thus the propagation rate of light slows down from approx 300,000 km/s in a vaccume to 225,000 km/s passing through water (ri 1.3) and about 200,000 km/s passing in glass (ri 1.5).
Light passing by massive stellar bodies, near gravitational anomolies, or black hole singularities will also undergo time dialation which means we must apply the rules of General Relativity and not Newtonian mechanics or simple trigonometry to determine actual travel time... But there is no way to know what regions of space that light has traversed through, how many black holes it passed, etc.
To put it another way, light traversing through nebulas, unseen plasma clouds, gas formations, any regions of space that aren't a perfect vaccume will slow light down over its millions/billions years of journey across the cosmos giving us the wrong estimations of time and distance.
To further add to this complexity, none of the stars we observe today are where they _appear to be_ at this current moment in time to us here on earth. We are looking backwards in time as we look farther out into space. If space or time have evolved or changed at all in the last few billion years (inflation) then our calculations could be off by several orders of magnitude as well.
Another big issue related to measuring distances at cosmic scales is that we are moving through space at an incredibly velocity (distance/time). We are NOT a stationary static observer at a fixed point in space, on the contrary, we are revolving around the sun which itself is revolving around the center of the milky way which itself is moving through space at incredible mind boggling velocities. It takes earth approx 250 million years to make a full rotation around the milky way center and our estimated velocity currently is 828,000+/- km/h through milky way space!!
Our movement through space also greatly affects the accuracy of our measurements of both time and distance as we are within a time dialation bubble we call earth, that is itself within another SpaceTime bubble we call the solar system, which itself is within a larger gravitational bubble we call the supermassive singularity at the center our Galaxy (Sagittarius A)...
Thus we must factor into our calculus that time is not linear across space. On the contrary, we are within several gravitational (SpaceTime) anomolies that affect the rate at which time "flows", and thus the rate at which light propagates across space must also be affected.
We also assume the measure of a meter is the same across all of space, such that all of space is not only flat, but uniform with no curvatures or differences in uniformity. Thus a meter is a meter no matter if we measure at earth sea level, or the surface of a star, or the event horizon of a black hole... But I digress, a topic for another _time_
Love your videos, keep it up!
One cool fact about the Moon reflector is that it is a retro-reflector, just like traffic signs and bicycle wheel reflectors. Its surface is made up of triangular indentations with interior angles of 90 degrees (corner reflector), which causes the radar signal to be returned at the same angle at which it arrived. This means you don’t actually have to be extremely precise to hit this small target.
This is a perfect video.
Everything got covered.
Everything got linked.
AND, you mentioned that galaxies where closer than the light shows. This is something that a lot of other scientiests forget to mention and thus the viewer thinks the distance in light years was the actual distance. Finally someone mentioning that this is only the distance the light has crossed.
Cheers
Glad you liked it 🤓
Nice technical conversation! Well done to both of you!
Thanks!
This may be one of my favorite science videos I've seen. I already knew the majority of this stuff separately and relatively knew how they work, but i always got confused when it came to understanding them collectively and how they all apply to one another. This video essentially just bridged the gap of my knowledge and understanding that i was lacking in order to actually understand it. Thank you very much for making this amazing video. You certainly earned my subscription.
Glad you enjoyed it.
That was really interesting. I knew most of it already but the part about red shift not giving the distance then or now but only the time of light travel blew my mind a little bit.
Emily is a great addition. I very much like it when she contributed.
LOVED this video. Best explanation I have ever heard of the whole subject.
These conversations are some of my favorite videos of yours! Thanks for them. They're REALLY helpful!
I love this format. The back and forth between you both is really useful. Great video!
Thanks! You're not alone in that opinion. They always perform better than my other videos.
This is the most interesting video you have published, and I have seen lots of your uploads :)
You're amazing. Your wife is amazing. You both make us feel part of the conversation! Thank you a lot!!
I can say it again and again. Your way to explain and visualize is just simply THE. BEST. WAY for understanding. Thank you a lot!
You two are so freekin awesome together! Love it!
And I would watch a 2 hour video on the nuance of why Type 1A Supernovae are only "about" 1.4 SM. 😊
Almost first.
Lovely to see your wife in the episode. Your coupleness is adorable.
Wouldn't a really long ruler work (preferably marked in metric)? It might take a few years to measure out a parsec, but I think I could do it.
The mass of that ruler would get big pretty quick, like to the point that it has its own gravity and is no longer reliable.
@@ScienceAsylum Just use carbon fiber bro
@@ScienceAsylum It would turn into a spherical ruler, right?
@@canuckprogressive.3435 ... and then eventually a black hole
Gravitational slide rule? That would be a science project @@ScienceAsylum
The distance ladder is one of my two favorite topics in astrophysics!
The second is stellar lifecycle/nucleosynthesis.
Have you ever considered doing a two parter covering the H/R diagram and stellar lifecycle and following it with an explanation the technique of using the position of the asymptotic giants from a globular cluster on the main H/R diagram to date the age of the cluster due to the relatively short time span spent in the asymptotic giant phase as opposed to the main sequence phase?
I think it is really neat that the horizontal line of asymptotic giants almost acts like a moving clock hand moving vertically down the main sequence as the larger hotter stars die out and the smaller cooler ones live longer.
I like how the two of you interact so well and respect each other's intellect. Keep up the good work! And thanks for explaining why my ladder doesn't reach the roof without using radar, or something like that. LOL
That was one of the best explanations of the subject, or similar related ones, I’ve seen in a long time. Made me so proud of science, rational thinking, knowledge and understanding.
Your lovely wife is a positive contributing 😊❤element to your programming. Emily Rocks!
I’ve been taught the wrung concept before, and understood it, but this was some amazing review. Probably the clearest presentation of these concepts I’ve ever seen.
There's one bit about this I think is missing, which is how we know that the logarithm of the period of a cepheid variable is proportional to its absolute magnitude. There aren't enough of them that are close enough to measure the distance to for us to do good statistics. The way we determined this was by measuring the apparent magnitudes of many cepheids in the Small Magellanic Cloud. It was already known that stars within this cloud were associated with each other and thus at roughly the same distance. (The cloud is large, so there will be a variation in distance of a few percent, but that should average out.) We still don't always know exactly which stars are associated with the cloud and which are foreground or background stars, but the vast majority we see should be in the cloud. By measuring and plotting the apparent magnitudes and periods of thousands of cepheid variables in the SMC, Henrietta Swan Leavitt was able to show a clear linear relationship. And since they are all about the same distance away, that means their absolute magnitudes must have the same relationship (to within a constant).
Once this relationship was known, we could accurately measure the distance to nearby cepheids using parallax in order to get the constant of proportionality.
The trip is not frustrating for the photon. The trip is instant, traveling at the speed of light. but mostly because photons don't have feelings.
How can it be instant when light still travels at a specific speed ?
@@michaelblankenau6598 Relativity. The same way the guy on a train sees and hears differently than the guy standing still as the train passes. Moving at the speed of light means also there is no time. Very tough to get your head around. Keep thinking about it and you will eventually understand it. But a wise man once said if you think you understand it you really start to realize you don't understand it and it's true. You have more questions.
These videos are awesome. I love how informative every example is. Thank you for all of the work you do for us.
Awesome video, great explanations of the techniques used! Could we make a better model of the expanding universe and position/distance of far away stuff if we’d be able to very accurately measure the red shift (frequency) changing over a large period of time?
Explain how gravity works to her and us.
Space expands faster than you can measure it 😊
True.
Always loved The Sciences especially astrophysics and particle physics and it is refreshing to have the subject matter revisited with fresh updated perspectives in order to expand my understanding.
You're wife is SOO witty 😂 hilarious 👍👍
Thank you so much for this video. I would describe myself as passionate about space even though I don't have any formal training. This wonderful explanation of how we got the distance of space around us right and what we used and how we used it is awesome.
This is the best explanation of the distance ladder I've seen. Great job at making a technical topic palatable for the lay person! Keep up the great work!
Thanks! Worked hard on this one.
Distance verse Time is an interesting thought process. "How far away is the green from my golf ball?" Verse "how far away is Walmart from my house?" The first question you would answer "240 yards" since you need to calculate what club to use... And the 2nd " about 5 mins away" since all you care about is using a car to drive there.... And what blows my mind is that everything a human sees or hears is in the past... If you looked up into the night sky and saw a huge asteroid smash into the moon... It actually happened 30 seconds ago due to the amount of time it took the light to reach your eyeballs... Same with seeing a friend smile... It took time for the light reflecting off her face to reach your eye balls.. It's very small but it's still in the past lol
What a great video! Honestly, I very much enjoyed being educated and entertained. You guys seem very genuine and expressive. Thank you