How is it possible to measure the distance to stars and galaxies?

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We can’t use tape measures, rulers or lasers to measure the astronomical distances to stars and galaxies, so how do we do it?

Music Credit: Stellardrone – Cepheid

Comments: 100
  1. Brad Heilman

    Does everyone in here know that the Earth and the Universe are only about 6000 years old?

  2. Matthew Pohlman

    This is complete science-fiction. Please stop believing all of these stories. In no way have any of these claims been observed by any human being in real time or space.
    Let’s please also give credit to the specific ‘scientists’ who have invented these methods of intergalactic measurement. Why do we just call them ‘scientists’? Imagine if Mozart or the Beatles were just referred to as ‘musicians’.

  3. Logan Floyd

    Alex, your videos are literally one of the most well put together space videos on youtube, AND you upload so often! The visuals, the audio, your calm and collected voice, PLEASE never stop doing this!!!! By next year, you’re gonna have so many subs its gonna be insane… Keep it up!

  4. voidremoved

    God is real

  5. Mumen Rider, Bicyclist for Justice

    Answer.. you can’t without assuming the radius of the earth, and the actual circumference of the “path around the sun”.

  6. Engelton182


  7. Abhijit Dhar

    Alex you made my Christmas and Happy Christmas 2 U

  8. Joe Deglman

    The problem with measuring distant stars arises from the erroneous use of redshift due to doppler or and expanding universe idea. None of those redshift-expansion models give a coherent rate of expansion.
    This is mainly due to the fact that redshift has been shown by studies of refractive index, flux density, and GPS, to be due to flux density or back-emf, and not due to doppler. The light emitted is due to the flux density in the area where the vibration originates, and not due to doppler.
    Once we reconfigure these expansion models, and redshift based upon flux density and not doppler, especially for quasars, we will get a steady universe expansion rate of zero, and will get a better idea of the distances to these distant objects.

  9. Epic Gamer


  10. David Allison

    How is the parallax system possible if our sun is revolving around the center of our galaxy?

  11. John McCabe


  12. adamdecoder1

    Nooooo Alex says Nukular and not Nuclear :( My day is ruined

  13. quest 77051

    so it’s a guess. it’s not actual?

  14. Mr. Zelice

    Hey Astrum i dont know if you are born in switzerland or moved to switzerland thats why i speak ine nglish right now:
    how do they know which star/planet it is in the sky directly? i mean they dont have a nametag on them ;D

  15. Leo Staley

    If anybody wants an even more in-depth lesson on this should look up David Butler’s “How Far Away Is It?” series here on YouTube. I need to speed him up to at least 1.5x speed because he talks slow, but he makes such amazing educational videos.

  16. Mark s

    If you are lookin at something that’s 1 billion light years away, how do you know there there,if it takes the lite ,1billion years to get to your eye.

  17. Felix Antonello

    Your so pleasant to listen to, I always look forward to your uploads mate

  18. Daniel Belayneh

    I couldn’t quite understand the meaning of this statement at 3:38:
    “A Cepheid Variable is a very special type of star that changes in brightness periodically depending how bright it is”.
    1. Because it is referred to a star, does that mean “Cepheid Variable” a name of a star?
    2. Can it be said an object “changes its brightness depending how bright it is”? Does it make sense?
    Wouldn’t that be tantamount to saying “So and so is a very special type of darkness that changes its darkness depending how dark it is”?
    “So and so is a very special type angle that changes its angles depending how angular it is”?

  19. volarecantare

    Simple answer in one word: Trigonometry.

  20. Trance Emerson

    in ancient times, there were some people trying to figure out how to find the distance to far away objects, a man named Pythagoras came along and said “try angles” who subsequently died in an attempt trying not to run the hypotenuse of a right triangle through a bean field. surely he must have known he and the men pursuing him would destroy someone’s hard earned crop.

  21. Wayne The Seine

    Can you explain lensing…..isn’t this also a method of calculating distances?

  22. Malcolm Canning

    U can convince a sheep

  23. Bridventure PR

    Thank you for this informative presentation. The idea is to use the best indicator of distance, thus minimizing the approximation. Of course, then there is also the spacetime relativity conundrum! 🤔😑

  24. Lipi19821

    I think inverse square law makes star light imposiblle to travel(see) over distances astronomers say they are traveling..
    Wiki:/// an approximate threefold increase in distance results in an approximate ninefold decrease in intensity of radiation( /brightnes)
    so imagine how bright is a star that we can see from earth 100 milion Light years away if we look at it from 1 lihjt year away….I would say those brightneses are imposiblle…

  25. Pär Landor

    Thanks for this vid. But what are we measuring? The distance to the visible light is not where the star is anymore.

  26. IdkWhat NickBeOn

    Simply put…it isn’t


    Long ruler 🤷🏻‍♂️🤪🥳

  28. fam rombouts


  29. zaini ikhwan

    Great video as always Alex!
    Dang that last part hit me hard _(:’3JL) _

  30. MusicalRaichu

    talking about parallax made me think … what if we put a telescope in orbit around jupiter and measure parallax from there.
    it would be a long-term experiment 6 years (half of jupiter’s year) plus the time it takes to build it and get it there.
    at 5 times earth’s diameter, it means more accurate measurement of more stars, and maybe we can use the data to refine other distance methods.

  31. Steve Drive

    favourite space channel on youtube

  32. Patriotgal1

    I worked as an astronomer in a 100 year old program, measuring stellar parallax at the Leander McCormack Observatory in the mid 80’s. Working with that beautiful Alvin Clark 26-1/4 instrument. Very interesting job. Photographing the target stars soon after sunset, or close to sunrise. We used glass plate film as it was dimensionally stable. After they were developed and dried, they went to the measuring room. Then much data entry.

  33. Karim Amin

    But how do you get the diameter of the earth’s orbit?

  34. mnemonic brian

    How to measure the distance to the sun?

  35. Daniel Dulu

    bottom line, it’s still experimental and theoretical. I always assumed we knew but obviously there is more work to do. The distances are staggering, impossible to phantom in our own minds which is why they come up with these theories.

  36. Scientific Humanist

    It’s too bad you failed to mention the brilliant woman, Henrietta Levitt, who discovered the Cepheid Variables method. Edwin Hubble then used her invention to measure the distances to nearby galaxies and achieved fame (and maybe fortune) while nobody bothers to mention poor old Henrietta. 😉

  37. rymond sp

    Thanks man

  38. Grzegorz Kapica

    You show the main sequence stars diagram. But there are multiple sequences available. How do astronomers know, which to pick?

  39. creepy whiteTrash

    ASTRUM ADVICE NEEDED: today I had a think, I dont know if this is already a theory but could at least some terrestrial planets be objects that originated in the kyper belt and beyond and just got sucked into the centre of the solar system while the gas giants were forming?
    This would change a lot of things, I dont see a reason why it couldn’t, what do you think?

  40. Mai Mariarti

    This is all assuming speed of light and gravitational forces are constant all around the universe.
    Assumptions are often wrong.

  41. Md Waqas Shamim

    thanks for very informative gift video in my birthday

  42. AJAY


  43. iamsicko

    YouTube is not notifying me about your vids even tho I have the bell on

  44. Muni Sharma

    2 days ago I was discussing with someone about the distances , that they measure it, scientists or nasa says and we believe….
    And today here it is., The video I wanted.
    Love from 🇮🇳❤️❤️INDIA.
    I WATCH UR EVERY VIDEO IN 1080P OR 4K . especially those highres ones.
    All the best

  45. TheEryk

    I think the universe have no end. So there is infinity other lives in the universe.

  46. MrKroxan

    I wonder how bad future generations will see us when the real space exploration begins and what we consider to be reality now turns out to be a fairy tale, as well as the dragons that the ancients drew on their maps when they began to sail the seas.

  47. Snipo X Killo

    Guys from asia! We will be able to witness an annular solar eclipse on 26th Dec (4″30 AM UTC 10 AM IST)! Looking forward to it!!


    astrum hello your biggest fan and I want to tell you can you make a video about Jupiter moon ganymede

  49. Dreamrider


  50. andymouse123

    Why don’t you SAY standard candle ?

  51. Albert Dadze

    Sometimes I get tired of listening to space related videos, because of the vastness of it, its infinite size, the idea that the big bang creating the universe because of its expansion blah blah blah but I love Astrum as he explains it in simple words by mind can understand. Gosh it is so possible, there are others on other solar systems in our galaxy and other galaxies.

  52. kirby march barcena

    I’m glad scientists and mathematicians found a way to measure distances in light years.

  53. uglyduckling81

    Whilst I find space information endlessly interesting I can’t help but think it’s mostly pointless because of the massive distances involved.
    Unless we can invent or discover what is essentially space magic to break laws of physics we are in reality confined to this solar system.
    It’s not like there isn’t enough opportunity here anyway.

  54. cannibalbananas

    @1:30 How does this work if things aren’t fixed? In the car scenario, a house & hill aren’t moving, only the car. In space everything is whizzing around, so where the stars were 6 months ago is not where they are today. We’re not even in the place.

  55. LAudioS

    First You have to explain how did you measure distance between earth and the sun .
    starting with wrong premise will definitely give you wrong result .
    keep trck-gonometying

  56. d0min0danc1ng

    Not to be confused with Buffalax
    Girly mannnnnn…girly man

  57. 1_2_Die

    What grade of improvement with the parallax method could we gain, if we would launch 2 probes to Neptune orbit (opposite to each other)?

  58. 7facebook

    I wish in 2050 the measurement will be – it is 1 second to get to Alpha Centauri

  59. Kerstin Nilsson

    It’s such a shame we were born too early to ever reach any of these things

  60. Coalition of Rob

    I have wondered, thanks

  61. Peet du Toit

    Happy Xmas Alex. What an amazing video

  62. NoneOfYour Beeswax

    Great stuff as usual; very well explained with excellent graphics and editing. After such shameful brown-nosing I’d like to put in a request… any chance of doing a video on HD 140283, popularly known as the “Methuselah Star”? It’s fascinating in itself and it does bear upon the science involved in measuring age/distance of stellar objects.

  63. GuitarZombie

    The SWAG method is used for this

  64. Rob Sin

    Alex, where are you from.🙏🇦🇺👍

  65. Christopher Hager

    Thank you for that information.

  66. Valarmathi Bhaskaran

    Hello!I’m here! I have a lot of interest to study and make videos about space. But I can only study about space, but cannot make videos because I am 10 years old.

  67. She's my President

    How do we know the actual physical size of stars ?

  68. kvykimo indelis

    3:41 wat

  69. aviral gupta


  70. julian wilton

    With the rocket technology we’ve currently got, forget about ever trying to cover those vast distances in space. Excellent video.

  71. AJ81

    Excellent and informative upload, sir👍

  72. Andre Souza

    Thumbnail already gave the answer

  73. fintan bourke

    Thank you for making these videos…

  74. Scribbli Chheery

    New sub 👍Love your content (and your voice). Hope you get 1M subs soon!

  75. Leon Ackermann

    I´m commenting here because it´s your newest video. I´m interested in Space since 3 years now, your videos are the best i have seen so far. You present the facts easy to understand for everyone, but also with great pictures and realy interesting graphs and comperisons. Great work.

  76. mjncad

    Thanks for the overview on the methods beyond the Parallax Method for distance measurement.

  77. Retriever

    your voice is soothing and calming thats why i watch u over others lol

  78. Don Hendricks

    Very interesting! Thank you so much for this video. Loving your channel! Cheers.

  79. Andy E

    Makes me so depressed ill never be able to see other stars, world’s and galaxies in real life 😔

  80. TROTH

    I have learn’t a lot with these’s video’s , they are very educational , thanks .

  81. sayyed abbas

    Hey Make video about our nearest neighborhood star

  82. Chris Coker

    Albert Einstein told you how to do it follow his instructions

  83. Alex Bichkovsky

    Great background sounds

  84. Jezza Lenko

    Everything has already happened out there ..perhaps it’s already over…

  85. babyrazor

    planing on a trip? well send us a postcard when you get there. Oh, and watch out for the variations in the vacuum of space, it’s not uniform you know. things may be closer than you think and the trip may be longer.

  86. Chromodynamix

    Can you do a video about the sky coordinates astronomers use? :)

  87. Danny Fubar

    Math is witchcraft! A good length of knotted rope will get me close enough. : )

  88. Purge boy121

    1 light year should be called 1 never never year

  89. Couch_Ech

    You explained this with amazing detail that i can understand. Thank you.

  90. creepy whiteTrash

    I love how much your videos make me think. I’ve watched them all a few times each. I showed my wife this one but she didn’t care for it 😂

  91. Slaphappy Duplenty

    That thumbnail. Brilliant.

  92. Artist N Recovery

    I love this channel.
    Trying to incorporate some of these awesome production values, into my videos.

  93. Particulator

    An Astrum video on fridays makes an excellent start for the holidays.

  94. Starfish Prime

    Now I finally know how! THANK YOU ALEX!

  95. Zhander Drake

    I never actually thought of this question…. Great vid

  96. aXel Red

    much needed video thank you, and I can’t tell how much i love your voice.

  97. Esat Becco

    Can you also make a video about how masses are calculated/measured in space?

  98. The Exoplanets Channel

    I wish all the measurements were wrong and the closest stars were actually 1 or 2 light years away.

  99. Master and Servant

    2:15 This diagram is called H.R. or Hertzprung-Russell, which is useful to classify the stars upon their brightness, size, and heat, There is a common joke about the letters used to determinate which kind of star are we dealing with, our Sun, for instance, is a G2 class star, every letter is divided into 10 values, so, a G3 star is slightly different to our Sun, but, In University days, there was a mnemotechnic trick to remember those letters’ order so they are O B A F G K M, which would stand for “Oh, Be A Fine Girl, Kiss Me..!

  100. Ali-K

    Feeling happy to be a member of this channel. i would love to support your hard work. This is simply the best space channel on youtube. In these holidays i hope you make more videos :)

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