M25 - Measuring the distance to stars - Deep Sky Videos
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- Опубліковано 7 сер 2024
- Professor Merrifield discusses motorways and stars - but says only a little about Messier 25 itself!
More Messier Object videos: bit.ly/MessierObjects
Includes discussion of the Baade-Wesselink Method and cepheid variable stars.
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Video by Brady Haran - Наука та технологія
All the profs are across the various channels are brilliant but Professor Merrifield is particularly good at explaining things to me. His videos often leave me with not only info on the given topic but an understanding of how the info fits in with the rest of the universe.
I 2nd you. But I usually set the speed at 0.75 to slow him down.
Agree as well. His explanation of the fundamental geometric properties of spheres, measurement of surface area, calculation of star brightness and from this, calculating change of radius and then total star size are elegant, simple to envision and to remember (even if not perfectly accurate).
When you see an explanation on TV of how Cepheid variables are used to measuring stellar distances it's usually simplified to the point that it's nearly meaningless. This was brilliantly clear. Thank you Professor Merrifield (and Brady) for the excellent explanation.
RMoribayashi bear in mind there is another more common way to exploit Cepheids as distance indicators, which is to use the fact that there is an empirical relationship between a Cepheid's pulsation period and its luminosity, so if you measure over how long a period it changes in brightness, you know its absolute luminosity; looking at its apparent brightness then gives its distance. Note, though, that this is a "secondary distance indicator" that only works because it has been calibrated to an absolute scale by more fundamental methods like the Baade-Wesselink method described here.
Michael Merrifield Yes, it's usually the method you describe that documentaries describe. I could never figure out how the first few were calibrated. Now I know.
I was just thinking that. He's really good at explaining things without dumbing them down. This is part of why DSV is one of my favorite UA-cam channels.
This is probably one of my favorite videos from this channel. I am so amazed at the fantastically complex problems humans are able to figure out. And the way Professor Merrifield talks about this is just so captivating! I really love when he's in your videos because he just has this way of describing things that makes me want to listen for hours on end like so many other people have said already. Professor Merrifield and all the videos on this channel make my thirst for knowledge a million times more intense than it already is! I can't wait to start my astronomy major!
Thank you for these videos, Brady. They're truly fantastic and the world is a better place for having them!
Have been watching the back catalogue of deepsky videos and really enjoying them, so glad prof Mike and colleagues take the time out of their day to do these
Hey Brady, what about a video to explain what all those prefixes like M, U, IC, HD, HR and others mean, what's their history and what are being used right now? I do know myself but I think there are many viewers to whom they are just random names and numbers of the same object.
The professor seems so interested in what he's talking about that it makes me more motivated for studying. Thanks Deepskyvideos!
I love this channel so much. Space can be confusing, but you guys make it so easy to understand!
Jesus Christs, how good is Merrifield?! I wish he was my professor for every class I had in my life.
The M25 in London is small, the other M25 is far away.
Why is this not the top comment?
Ah forget it!
my goodness, thats quite a claim
...feckin ijit...
Where's Tony Lynch off to? Probably to get some heroin!
I really appreciate and enjoy these explanations. Understanding the seemingly un-understandable is put together piece by piece.
Thank you Professor Merrifield. :)
Clicked this video expecting it to be all about parsecs, but instead was introduced to various other methods of measuring distance to stars, and surprised to learn that they are actually older than measuring paralax measurements. Very interesting stuff.
1:25 I love this 2 second moment of frustration from Merrifield. It's like a 1 out of 10 on the frustration scale. It's like the plank-length equivalent of annoyance.
that is an amazing story. Thanks Professor and Brady!
YES A NEW DEEP SKY VIDEO. thanks Brady. I knew it was all about me..
This is something I've always wondered, how they can figure out position of something and whether or not it's bright because it's closer or bigger or hotter etc. Really great to hear this explanation and glad it's not hard to understand.
Thank you for those nice explanations, really
Yay! More Deep Sky videos!
great video professor Merrifield
The video answered a lot of the questions I had about measuring the distances to stars.
Thanks a lot
Loved the Father Ted reference :)
Thanks... always wanted this explained...it's difficult to find this level of detail info on it
Thank you sir for teaching us
so how far away is M25? or did i miss it?
O love videos with this prof
Father Ted is awesome, thanks for recommendation.
you guys should make a video about how they find the age of stars and how they discovered how long they last, maybe a continuation of the Pleiades video.
Those studying under Prof. Merrifield are very lucky.
that was a very interesting video
I'd like to hear more about the Gaia telescope when there's more to report. Thanks for these Brady.
This is very interesting -- my thanks.
The clever ways they figure out to study this stuff is as cool as what they're studying
Great video, definite thumb up, an extra one would have been given for the father Ted reference :)
Thank you, interesting video :-)
Cool!
I have had very good astronomy teachers. However, I love this man's pedagogy. Next time I'm in the UK, screw going to the Eye of London -- I will beg to sit in a class!
Wow!
Just realised that the animation is showing a star with a hotter surface when contracted (not contracting) and having a cooler surface when expanded. Though this happens, it's confusing given the talk of Doppler shift.
Considering the fact that the professor specifies unchanging temperature in his explanation, I suspect that it actually is intended to show Doppler shift, and that they got it backwards.
In the book Good Moens, by Neil Gaiman and Terry Pratchett, they talk about how the M 26 motorway was designed by a demon as a massive joke on humanity which raises the sin level every day.
Wizard Dragon Good Omens?
wjvanzeist Yes, Stupid typos :)
Well, it's a very clear explanation of how to determine the distance to the cluster, but the punch line is missing--how far away is M25?
4:07 what about red-shifting from the expansion of the universe? Wouldn't that affect the emitted light so that we wouldn't be able to determine what colour (and temperature) the star had? If we try to find the distance to one particular star we can't know how much its lights wavelengths has been distorted.
The professor mentions parallax at the end. Since the accuracy of a parallax measurement is driven by the distance between the two observations, has any consideration been made to putting a telescope many AU out from the Sun - perhaps further than Mars - and using that instrument to measure stellar distances via parallax? Or would the increase in stellar distance measure capability not be worth the cost. (Of course, said telescope could be used for many other measurements).
tscoffey1 I was actually thinking the same thing. We could also just use two satellites, put them on the same orbit around the Sun as the Earth on opposite sides of the Sun.
Although I think we could do longer distances if they were in orbits further out, but either way I'd love to see this done.
gaia does exactly that en.wikipedia.org/wiki/Gaia_(spacecraft) although it was parked at sun-earth L2. i think for anything further than mars the time requirements would grow exceedingly high, at jupiters orbit you'd have to wait 6 years for a single dataset of two images...
What are some practical applications of the knowledge obtained from astronomy? I have thought about it and came up with a handful. Maybe there are others I've neglected to consider, if so please add them.
1. Space events early warning. (Collisions with meteors, asteroids, solar flares/storms/spots, etc.).
2. Guidance for a more successful search for extraterrestrial life.
3. Navigation data for space probes and other data gathering devices sent into space. (probes, satellites, etc.)
4....?
I have deliberately ignored the sort of benefits gained which could be cataloged under the general "Increasing our understanding of the Universe and everything within it" sort of banner. I am particularly interested in the direct, immediate and practical applications of astronomical knowledge.
You think your object is messy? Well, this is a Messier object.
Noob question Re the radius of a cepheid variable star. Is the radius calculated at its most compressed size, its most expanded size or some mid point ?
Correct me if i am wrong, but measurements based on a paralax shift counts as well as a relative measurement for if the position of the reference body is within a certain amount of precision, then the position of the star in question is as well. I may think of reasons where you can neglect that for you can find stars so far out that virtualy no movement can be detected. But that doesn't change the fact that it's not a means of measuring absolute distances.
If someone would be so kind to enlighten me over this topic? :-)
Please forgive my english
DasIllu The key is to pick background reference objects that are so far away that they exhibit essentially zero parallax. Given that, measurement of parallax of foreground objects yields a direct determination of absolute distance.
The method is not "relative" because you are not comparing one parallax against another. It's "absolute" because you are measuring the actual parallax of the foreground objects by choosing stationary background objects as reference.
Farther Ted is great
They forgot to mention the very commonly used relation between a Cepheid variable's pulsation period and absolute magnitude, which is used much more than the method he talked about.
2:44
I love Father Ted!
Would we be able to get parallax values for far more distant stars by taking the measurements from Mars?
yep. indeed we could. we'd have to know how far away the satellite orbiting mars is from the one orbiting earth. but the 2 planets are close enough to use atomic clocks to send a signal from mars with an exact timestamp of when it was sent. then ts simple speed and time math to get the distance. would probably be more accurate than using the earth on both sides of the sun to do it actually.
I'm curious, what would cause the variable stars to expand and contract that much?
Here is a quote straight from Wiki (hint, hint):
"The accepted explanation for the pulsation of Cepheids is called the Eddington valve or κ-mechanism, where the Greek letter κ (kappa) denotes gas opacity. Helium is the gas thought to be most active in the process. Doubly ionized helium (helium whose atoms are missing both electrons) is more opaque than singly ionized helium. The more helium is heated, the more ionized it becomes. At the dimmest part of a Cepheid's cycle, the ionized gas in the outer layers of the star is opaque, and so is heated by the star's radiation, and due to the increased temperature, begins to expand. As it expands, it cools, and so becomes less ionized and therefore more transparent, allowing the radiation to escape. Then the expansion stops, and reverses due to the star's gravitational attraction. The process then repeats."
SayNOtoGreens Thanks
What specifically has made determining distances using parallax more accurate? Using different points in our solar system to increase the angle?
Equipment with better angular resolution so that parallax angles are more easily and effectively measured. Probably lol.
*****
Except that we can't do that. Or do you know a way to change Earth's orbit? ;)
Alexander Rudasi
Mostly the fact of building specialized satellites just for that purpose. Look up, how "Hipparcos" is doing it.
superdau it would be possible if you would measure the thing from probes lets say from jupters or saturns orbit.
RamsesTheFourth Sure, but it would take much longer to get results. A measuring probe out at Saturn will orbit at the same speed as Saturn. Half an orbit is almost 15 years!
So, how far away was it?
At Five minutes or so, comes the hardcore question. How can we declare a radius of a star? The explanation of the professor seems to me quite concluding, but since there wer shown old pictures of Baade and his diagrams. Could it be that they were recording a "wobble" effect? There might be an early recording of a massive exoplanet orbiting its star. This is nowadays known as a method to detect those planets. But eventually I´m wrong because of the behavior of the particular star since not all are as calm burning like the sun, for example.
Here's something I'm wondering about. As our solar system orbits the center of our galaxy, doesn't the sun move around a ton as well during the 6 months our earth goes around it? Doesn't this screw up the parallax measurements? I understand the thing we're trying to measure orbits the center of the galaxy as well, but surely not every star orbits it at the exact same speed?
MadMetalMacho yes and no: stars do, indeed, move during the year due to their own orbit around the Milky Way, the fact that the Sun is moving, etc. However, the timescale for these motions to change significantly are very long (tens of thousands of years at least), so this motion is recorded as pretty much a steady drift across the sky, with the parallax effect a yearly "wobble" on top of that uniform motion. Both measurements are useful, though: while parallax gives distances, the steady motions tell us about the orbits of stars of different types in the Galaxy.
The pulsating animation - should't it be reddish when it shrinks ad blueish as it grows? The Doppler effect on a color of a thing going towards you makes it bluer afaik
multimotyl Thought the same. Actually, it should only be reddish/blueish *while* shrinking/growing, but return to a neutral white (or yellow or whatever) at the turning points of the process. But maybe the color does not refer to the Doppler effect but to the temperature of the star (smaller = hotter = blue, bigger = cooler = red).
Maybe... maybe.
Der Laschi yes -- animation shows the variations in colour that typically occur during pulsation (mentioned briefly in the video as something that makes the calculation a bit trickier. Doppler shift effects would be tiny on colour: to switch between red and blue, expansion and contraction would have to be a fair fraction of the speed of light!
Is the audio kind of quiet for others?
I don't understand the importance of the distinction between open and closed clusters. After all, all of the clusters discussed are photographed through a fairly decent telescope.
The star should appear bluer when expanding, redder when contracting and inbetween inbetween. P.S. Generally though, thanks for being part of my middle life renaissance...
Main effect in the animation is the temperature changes as star oscillates (mentioned in passing in the video) -- for Doppler effects to produce colour effects that extreme, it would have to be oscillating at a good fraction of the speed of light!
Chris Jordan The confusing point here is that the pulsating star in the video is not illustrating redshift/blueshift (the visual effect of that would be invisibly small), but rather the changing surface temperature as the star expands (getting cooler and thus redder) and contracts (getting bluer). Granted that it was rather misleading.
Our American friends? I'm a European, how am I supposed to know that the M25 is a motorway in the UK? I feel excluded :
DecileNeil Well, M(anything) is a motorway in the UK.
Americans occasionally use 'I' for interstates, but don't generally have a letter for our other numbered roads. To go to the mall, I drive down 15 and over 80 (I80), a distance of almost 16 miles. Now my stalkers can find me. :)
R3Testa More accurately we DO have letters but don't use them very often. Rather than say something like "SH102" we'll just say "highway 102." Then you have things like Farm to Market roads, which are almost always referred to as FM-###.
Or you could live in an area like North Texas where we have fourteen names for the same road. Are we driving down Boulevard 26, Highway 26, or Grapevine Highway? McLeroy Blvd becomes Western Center turns into Watauga Road transforms to Mid-Cities Boulevard before becoming Cheek-Sparger and then going back to being Mid-Cities. *HEAD ASPLODE*
DecileNeil UK has no friends in Europe, so....
*****
Does that mean the English are on speaking terms with continental Europe, providing the Europeans speak using the proper English language ?
*****
Of course you're right. I'm just having a bit of fun by exaggerating the truth ( insert dry humor face here ).
But you have to admit, there is a grain of truth to it :-)
Volume problems in this video. :(
Isn't the depiction of the Doppler effect during the star expansion/contraction cycle the wrong way around? Light waves emitted during the expansion get "compressed" and therefore blue-shifted, while the opposite occurs during contraction. The video shows red-shift during expansion and blue-shift during contraction.
+Markos Strofyllas The temperature change is what can be seen. The star would have to expand at a speed comparable to the speed of light for the Doppler shift to be visible.
+Kenneth Florek as per the video. we can now measure the doppler shift caused by an expansion/contraction of 1 kilometer per second. far below the speed of light.
Robert Pruitt
It is remarkable what technology has achieved.
Because 3,600,000 kilometers per hour is well beyond the range of earthly velocities, I think 1/300 of the speed of light would count as being comparable to the speed of light. But I don't believe that human vision would see 1 part in 300 shift in color as changing from red to blue. It is my understanding that the variation in color that we see is due to temperature.
+Kenneth Florek while I'm not sure of the sensitivity of the human eye, we do use machines to measure the color.
you are also partly correct. color is related to temperature.
but no matter the temperature, and therefore color of the light made, it still gets shifted based on direction and speed in that direction.
Oh, and literally speaking, color is just a measure of the energy of the photons. And just as literally, you can't actually see color. All em radiation is invisible. It is your brain that invents colors to go with the energy levels of the em radiation. But a machine can measure the energy levels very accurately, even if our eyes cannot.
Robert Pruitt
The only thing I am talking about is the illustration the original comment mentioned, and why it is as it is.
I think you are mixing two things that astronomers are saying when they speak of the color of stars. Leaving aside the emission and absorption lines in the atmosphere, stars emit a continuous spectrum of blackbody radiation which has a graph with a hump that is characteristic of its temperature. The curvature of this hump causes the star to look a different color as the temperature changes. Blackbody radiation at lower temperature has a dominance toward the red end of the spectrum.
Red Giants are not red because the emission lines have been shifted toward the red by Doppler shift.
When a star expands, the energy density goes down, which means the temperature goes down. The blackbody radiation looks redder. The reason is not Doppler shift.The absorption lines in the atmosphere no doubt are shifted higher in frequency.
But I have a philosophical difference of opinion. The meaning of color is whatever that perception is that a human has. Color is not the energy or frequency some photons may have, except figuratively, or by extension. It is reinterpreting human perception in terms of photons that misunderstands color.
While it is true that our brains invent color, it is also true that our brains invent everything we have in our minds, such as whatever we think of photons, so in the same sense that color does not exist except in our minds, photons, no matter how we conceive of them, are concepts in our minds and not the actual photons, so photons don't exist.The same applies to all physical phenomenon. You could name anything, and argue that it doesn't exist. That is not to say there is not something that our perception is based on.
M25 is 2000 light years away, in case anybody is wondering :-)
which stars are in the m25? im guessing at least john cleese pottering about in some silly car
HOLD on, A star expanding, by about 10% then getting 10% smaller every 7 days (See time 5:27), I do not believe that. How fast is that expansion?Let look at the graph, is it a sin wave?no , so if you place the graph in a FFT, you might see 3 sine waves.
So... uhhh.... how far is it to U-Sagittarii?
.
***** As a member of the open cluster Messier 25, it is about 2000 light-years distant.
If you weren't so London-centric, you could have chosen the M42, instead. I am sure the Orion Nebula would have been interesting.
Wow, he speaks very rapidly........
Thumbs up just because "Father Ted" was mentioned! :D
DeepSkyVideos 0:02 "....for our AMERICAN friends.." Really Brady? You know the world is made up of a lot more people than just Americans. You must know better since you're an Australian!
Adhiraj Sharma yes but Australians are super knowledgable about things outside Australia - I'm not worried about them not knowing what the M25 motorway is! ;)
Adhiraj Sharma Either you're in the British Empire, or you live in the American colony.
Adhiraj Sharma You are racist!!!!!! you called him an australian why do you have to bring up his race/nationality?!?!?!
Adhiraj Sharma I'm Norwegian and even i know English road designations. So yeah, it's probably accurate that only americans need clarification.
No, it would be like a mexican knowing american roads, which is more likely. The UK is one of the cultural hubs in europe, and as such people tend to know about stuff that happens there. And he was just extrapolating because it was a funny coincidence of a name.
Ah, so the M25 is kind of like the "punch bowl" in DC.
IC WEINER
Okay, there's a different method to measuring the absolute distance of a star and its called "paralax" ? But... you chose to explain how it was measured before.
conssavvas Briefly, parallax refers to the apparent shift of a nearby object when viewed against a distant background from two separate locations. If you, for example, hold your finger vertically a distance from your nose and then view the finger alternately with your left and right eyes, you'll see the finger shift with respect to the wall in the background. Similarly, if you take a picture of a star field, then wait 6 months (for the Earth to move to the opposite side of its orbit with the Sun) and then take another picture, nearby stars will shift in apparent position while very distant background stars won't move discernably. The angle of the shift gives a direct calculation of the star's distance, since the diameter of the Earth's orbit is known.
a star is a white hole from the antiverse, as the antiverse matter enters ours it reacts and then as the anti matter exits that hole into our universe the anti matter curls around and creates a ball and sun, the sun is powered by antimatter from the antiverse.
just my theory anyways.
GAME OVER "WE HAVE EVERY PIXEL COVERED" Alternately: physics.
I bet Prof Merrifield gets through a 50 minute lecture in about 20 minutes.
I fucking love math
FRIST!
ahahahhahahahahaha having to explain farther ted
first
pattt5408 No way; M25 beat you here by leaps and bounds.
You people need to research flat Earth. Check your ego at the door
adult place a call to go get it likely lead to a bakery in English it okay with you if I knew give me make a note 3 with Carl and Gloria in Tulsa
O my Lord. This astrology is some bull. Lol this man is talking like astrology is all about appearances and not actual measurements. Astrology is just like evolution. Not real knowledge.
*Astronomy, and both it and evolution are proven facts.