“The human mind is not capable of grasping the Universe. We are like a little child entering a huge library. The walls are covered to the ceilings with books in many different tongues. The child knows that someone must have written these books. It does not know who or how. It does not understand the languages in which they are written. But the child notes a definite plan in the arrangement of the books—a mysterious order which it does not comprehend, but only dimly suspects.”

Albert Einstein

Earlier today, I had the pleasure of visiting a high school astronomy class via Skype, answering some very good questions from some very enthusiastic and curious students.

But there was one question that we ran out of time for.

Image credit: 2P2 Team, WFI, MPG/ESO 2.2-m Telescope, La Silla, ESO.

How do we know how many galaxies are in the Universe?
While that’s a great topic for a blog post, I thought it would be an even better topic for an animated video! So for anyone’s high school astronomy class, or anyone with five minutes to spare, hope you enjoy it! (And don’t hesitate to full-screen it.)

For those of you curious about the original sources of these remarkable images and videos used in the creation of this, I couldn’t resist sharing these amazing resources with you from around the world, in order of appearance.

Video of Milky Way rise, by William Castleman.

Image of the southern Milky Way, by A. Fujii.

Image of the Orion Nebula, by Ioannidis Panos.

Video of a flythrough from Earth to the Virgo Cluster, by R. Brent Tully.

Image of the Milky Way, by Derek Rowley.

Image of Hickson 68, wide-field, by Gimmi Ratto.

Image of NGC 7331 by Paul Mortfield and Dietmar Kupke/Flynn Haase/NOAO/AURA/NSF.

Image of Stephan's Quintet of Galaxies, by Adam Block/NOAO/AURA/NSF.

Image of the star field near M31, retrieved from universe-beauty.com.

Deep image of distant galaxies with foreground stars, retrieved from universe-beauty.com.

And all the other images and videos are derived from these two fabulous data sets:

Images courtesy of R. Williams (STScI), NASA and the Hubble Deep Field Team.

And perhaps most spectacularly…

Images and videos courtesy of NASA, ESA, S. Beckwith (STScI) and the HUDF Team.

And here we are, less than a century after learning that the Milky Way wasn’t the only galaxy in the Universe, we now know that there are at least 100 billion of them, and possibly even more than that!


  1. #1 Mark V2
    October 13, 2011

    Thank you Ethan.

  2. #2 eNeMeE
    October 13, 2011

    Uhh, ditto.

    …Do I win a lamest post ever award?

  3. #3 NewEnglandBob
    October 13, 2011

    Nicely done.

  4. #4 MobiusKlein
    October 13, 2011

    Could you also estimate the count by looking at the count of ‘nearby’ galaxies, and scaling the volume to the volume of the universe?

    I suspect it would have a different type of error bar.

  5. #5 Collin
    October 13, 2011

    In the photo of the Orion Nebula, there’s what looks like a sort of conical shape with a light in the middle. Is this an illusion, or is it really shaped like that?

  6. #6 teo
    October 13, 2011

    Thanks!! Truly you capture the immensity and grandeur of space. Then you can extrapolate and are overwhelmed….

  7. #7 crd2
    October 14, 2011

    Do we stand any chance of ever seeing beyond the re-ionization period of the universe? Are there any ideas out there that could potentially allow us access to the 1st 400,000 yrs (aka the dark ages), or will that chapter in our 13.4 billion year history remain ‘dark’ & forever be locked away from our prying eyes?

  8. #8 rockyjoe
    October 14, 2011

    I am confused:

    a) If we are looking at galaxies from the early universe, then they should be from a much smaller universe. How can these be uniformly distributed from our viewpoint?

    b) Since we are viewing very old light, how can we know how many galaxies there are NOW?

  9. #9 Stan P
    October 14, 2011

    @ #8: I think rockyjoe’s question “a” regarding our viewpoint from Earth might be related to a paradox that baffled me wonderfully for many years: How is it that our sightlines into space can diverge forever but also converge to a point at the Big Bang?

    Robert Osserman’s lovely little book, Poetry of the Universe, finally showed me the light, so to speak. Osserman uses a simple three-dimensional analogy that enabled even lil’ ol’ math-challenged me to (sorta) visualize the path of light in four-dimensional spacetime. If you were a two dimensional critter living on a polka-dot planet on the surface of a spherical universe, and if light in your universe always followed the shortest path, i.e. a great circle, then your sightlines would diverge in all directions before converging at the point opposite your position on the sphere. But in reality, we are 3-D folk living on the 3-D surface of a curved 4-D space-time universe (a hypersphere if the curvature is flat, yes?) Light travels along the shortest path in spacetime, so our sightlines back toward the light sources must diverge in all directions.

    My head hurts from the effort of trying to wrap it around this concept. Ethan, could you please do a post on this sometime and help ease the pain?

  10. #10 Sian
    October 14, 2011

    A very beautiful and insightful video… and a John Fahey soundtrack. Wow.
    Thank you.

  11. #11 The Bobs
    October 14, 2011

    There is a better version of the Virgo cluster flight here:


    This one has narration and can be viewed in 720P. Try it at 720P full screen and it is awesome.

  12. #12 rockyjoe
    October 15, 2011

    Stan P. Thanks for the reply. I’m not math challenged, so I can understand the (Friedmann) equations, but the concepts are still confusing to me. I’m not sure I buy the spherical shell argument — as I think our universe is supposed to be pretty flat. The best I can do is to think of our view of the universe as being limited by the “fog” of the blackbody radiation, or more critically by the age of the universe itself — and that we are far enough inside the universe that anything we can see looks uniform.

  13. #13 Kenneth L Rothey
    October 15, 2011

    It is marvelous and amazing what a few billion bucks and good scientific theorizing can bring to us. Yet the question is more profound than the “chicken and the egg” theory. for instance, how did we get a picture of the Milky Way which itself is thousands of light years in (chose from the following 1. length, 2. width, 3. Height, 4. “the ends of being and ideal grace”.) By our own admission, our own spacecraft launched some forty years ago has only recently “left’ our solar system.

    Another similar question springs from a more recent picture of the universe which showed that ‘it’ was flat, just like the earth used to be. (I theorize that it was taken from the same theoretical camera which was used to take a theroretical picture of the Milky Way

    So in conclusion let me say in paraphrasing Einstein’s recently republished picture when there was some new evidence that there is a particle which travels faster than light, “I’m right, at least in theory!”

    Compound suppositions X 10 nth produce a universe which is expanding faster than we will ever be able to see. I suggest that we start with a smaller problem, counting the grains of sand in the shifting Sahara. When we are finished we will know that a grain of sand is itself a galaxy (in theory at least)

  14. #14 Ian Kemmish
    October 17, 2011

    For a schoolchild, the best possible answer is “we don’t”. Time learn about what knowledge is and what it isn’t.

  15. #15 torkan
    October 23, 2011

    i’m feeling myself so little right now,we are infact nothing but a dust in the universe!!blessed God who is the greatest….

  16. #16 torkan
    October 23, 2011

    how selfish is mankind that thinks is the master of the universe!!we are nothing but a dust in the universe!blessed God who is the greatest…

  17. #17 Jack Dawe
    October 23, 2011

    @7 There are infra-red telescopes capable of lifting the veil to some extent. But we’ll never be able to look back to the “moment of creation.”

    @8 From what I understand, there really is no moment of “NOW” holding the universe together in one simultaneous moment of time. Simultaneity (sp?) is one of the casualties of the Einstein Revolution. That said, by observing the relative velocities of distant galaxies, you might be able to figure out which ones merged and eventually formed elliptical galaxies, etc., so you could have a better idea of whether the overall number of galaxies approaching the present moment has grown or declined.

    Beyond which, keep in mind that Ethan is only talking about numbers of galaxies in the OBSERVABLE universe. If the UNOBSERVABLE universe is as huge as some cosmologists suspect it is (the Observable Universe being comparable to a proton divided by the Observable Universe, in size, relative to the Unobservable Universe), then you could cover the surface of the earth with googleplex exponential zeros and still not have a large enough number.

  18. #18 defarqua
    November 7, 2011

    As computing power seems to double every few years so does the estimate of the number of galaxies in the universe. I predict that by the year 2045 that number will reach one trillion.

  19. #19 nunu
    December 9, 2011

    If there is only one or two of some object in a trillion(s) does that make it less or more significant? What if there were 8/8 earths in our solar system instead of 1/8 earths, would that make earth more or less significant? What if there were just fish on those other earths, or what if they were full of billions and billions of other “earthlings”. Would that make the people on earth #3, less or more significant? It’s kind of creepy how we’re all alone next to big gaseous planets on a tiny little planet….with no-where with air to fly to…….(and an asteroid coming in 800 years!).

  20. #20 skipperblue1
    February 3, 2012

    Nicely done Ethan…the more this type of incredulous information on the vastness of the universe gets out to the general public, and in particular, to those that look to the stories of the Bible as to where it all started, the more they will convince themselves that it couldn’t possible have been created in the 6,000 yrs that the Bible tells us, but those stories where created by our ancient, and superstitious ancestors, who were looking for some answers, and hope for what happens to us in the afterlife…why is it that so many of the most brilliant and respected people of all time were non-believers of any religion, not just Christianity…Einstien, Hemingway, Frank Lloyd Wright, Sigmund Freud, Susan B. Anthony, Issac Asimov etc…even some of our founding fathers were non believers…Thomas Jefferson and Ben Franklin, to name just a few. But I would never suggest to the faithful to give up their hope of meeting their loved ones in the afterlife…if they need to believe that to get through this life, then it would be cruel to try to take that faith and hope away…

  21. #21 Mike Jackson
    May 15, 2012

    I know I can’t fathom the universe & its billions of galaxies & the vastness of each galaxy & the billions of stars in each galaxy & the billions of planets accomanying these stars and the potential for life on these planets in all these galaxies. But it is the single MOST intriguing THOUGHT and reality for ANY human!!! I am fascinated & overwhelmed by the wonders in the KNOWN universe & the beyond. How do the space experts wrap their minds around the fact that given the VASTNESS of the universe….when we had the beginning of the universe (the big bang) from the size of a “pea” & billions of years later we have what we have now. What was before the universe….what did it expand into? In other words what has it REPLACED!! Science says nothing was before….but if it was nothing then how has nothing become so vast to “HOLD” the universe ….”something” had to be there first.

  22. #22 Terry
    Brighton England
    September 6, 2012

    We look back in time and space and have ascertained that the the big bang occurred c13.7billion years ago. As light travels at a constant speed presumably we know how far that matter has traveled forward? ( which would give the size of the universe) or is the 13.7billion only relative to the time the light reaches earth? in which case I don’t understand how we have any clue to how large the universe is.

    November 15, 2012

    Universe is Expanding 72 kilometers per second, in such a case the center point of the Big bang explosion can easily be measured if we do it as fast as the universe growth. It seems to be endless and God has no Origin and End.

  24. #24 Wow
    November 15, 2012

    There is no centre. The expansion is universal.

    God doens’t exist. That precludes ending and origin both, so to an extent, you’re correct.

  25. #25 zak
    January 20, 2013

    I don’t remember reading anything in the bible or quran about all of this! can someone correct me? where does god mention the creation of all these universes and worlds.. the billions of planets and stars.. and who knows how many ‘worlds’ and lives are there among all these galaxies… yet the so called god was obviously unaware of all of this vastness.. and only mentioned what Man could already see and know back then, i.e the sun, the moon, etc etc how many discoveries do we need so that religious people can finally start doubting and abandoning their religions?? People still believe that with ALL that endless space around our planet, ‘god’ still forgot about everything in order to help Mary conceive!!

  26. #26 rich
    January 24, 2013

    as with all theological questions and as is written in our constitution, religion and intelligence, ie science, are to be treated as separate and equal (or something like that)

  27. #27 Wow
    January 24, 2013

    are to be treated as separate and equal (or something like that)

    No, nothing like that.

    They are orthogonal and unrelated.

    Science is about the world we live in.

    Religion is about fairy tales that make us think or behave in a certain way.

    Science CAN be taught in US schools.

    Religion CAN NOT be taught in US schools.

    Science DOES NOT get tax breaks.

    Religion DOES get tax breaks.

    Just a few of the differences.

  28. #28 Wow
    January 24, 2013

    how many discoveries do we need so that religious people can finally start doubting and abandoning their religions??

    It’s happening quite quickly.

    People are not requiring religion to tell them how things work, how to avoid disaster, how things happen.

    Religion is becoming little more than a social club (Which was probably how it started out too).

    This is why there are so many attempts to either ban science or get religion into schools again. Religion requires an extreme suspension of disbelief to get in to someone’s head, and that requires an unformed mind.

  29. #29 Sean T
    January 25, 2013

    zak and wow,

    I think religion’s primary purpose, at least for most religious people, really has nothing to do with explaining the world anymore. Science pretty much has that covered. The real purpose of religion is fear of death. Death is inevitable. Religion gives its believers the comfort of being able to believe that they won’t really die, but will continue to live on after physical death. Science, based on rationality and evidence, will never be able to give this comfort, which is most likely based on nothing more than wishful thinking.

  30. #30 Wow
    January 25, 2013

    Many are “socially XXXian”. Be it Jewish, RCC, Methodist, Mormon or Moonie.

    If they were REALLY worried about the afterlife, they’d be a lot more assiduous about keeping on the Good Word’s good side.

    Except they don’t.

    They will ignore the teachings if doing so means they live in THIS life more comfortably.

    Look at the Xtians who decry “Welfare Scroungers” despite JC’s story documenting his insistence that if there is someone who needs it, you must give them the shirt of your back, and you will be rewarded with life ever after.

    Or those getting up in public and proclaiming their holy richteousness, despite the word being that these people who pray loudly in public are not His followers, but that those who Pray in private are heard by Him Who Is Everywhere and will be rewarded.

  31. #31 Dan
    February 16, 2014

    It’s truly amazing how people can believe it all started from the Big Bang with a molecule ,but can’t conceive the idea of god,at least believing in god there is hope..there is a grand design,to believe that trillions of stars ,and billions of galaxies were created from a single atom is far more ludicrous than believing in god…

  32. #32 Sinisa Lazarek
    February 17, 2014

    @ Dan

    “It’s truly amazing how people can believe it all started from the Big Bang with a molecule”
    – well, maybe you believe that. No one here believes it all started from a molecule. lolz…

    “but can’t conceive the idea of god”
    – can conceive the idea. Choose to trust the data and evidence

    “at least believing in god there is hope”
    – substitute god with any other object and apply faith.. results are the same. So, indulge me, and worship your toothbrush for a week and see what happens. Confess to it, pray to it, adore it.. and see what happens. I guarantee you will find your toothbrush just as powerful as god.

    ” is far more ludicrous than believing in god…”
    – yeah.. and a concept of an omnipotent god needing humans as a sort of an aquarium to look at when bored is truly sane…

  33. #33 Sinisa Lazarek
    February 17, 2014


    “at least believing in god there is hope”
    Actually, this sentence of yours makes me sad. Sad because you see no hope in life without god. Without that father figure you believe your existance to be futile. I feel very sorry for you. You do need organized religion in order to tell you how to live your life. But not all do. Homo sapiens is not for everyone. To look at the world with your own eyes and realize you are all there is, and ever will be. No god, no nothing, only you and what you make of it. And be happy, because it’s the ultimate sandbox.

  34. #34 jeffntn
    June 25, 2014

    Demon Haunted World by Carl Sagan.

    The absolute guide to logical thinking.

    Not things being so because we wish it.

    Should be required reading, sadly, so many
    adults cannot wrap their mind around the truth.

  35. #35 ken
    United States
    April 2, 2015

    Science has theory after theory fail. Grasping at latest to “prove” self-creation. Logic knows an unknown can’t mysteriously appear without scientific explanation. WHAT IS THE ORIGIN OF THAT DENSE OBJECT???

  36. #36 Wow
    April 3, 2015

    Ah, so letting evidence change your mind is a weakness, only firm and unshakeable belief is allowed.

    ISIS are ABSOLUTELY CERTAIN that God wants them to create a caliphate and convert all heathen non-believers to their Islam.

    I guess you applaud that sort of unshakeable faith, hmm?

  37. #37 Wow
    April 3, 2015


    Yo mamma.