Very far

There’s a thing I don’t understand. Well there are a lot of those, but one in particular. I saw a re-run on Nova last night of a 2010 episode about telescopes and the universe. (As usual I was multitasking at the time, so I probably missed some technical information.)

They showed us one of the giant telescopes, this one in Arizona; the narrator said dramatically that they open the eight-story doors while we saw the doors opening. We saw lots of images via that telescope and the Hubble and others, while various people explained that they can see to the very edge of the universe.

That’s what I don’t understand. Eight stories tall, that’s all very well, but it doesn’t amount to much when stacked up next to the universe. Hundreds of billions of galaxies, you know, each with hundreds of billions of stars, all howevermany light years apart. Eight stories, one story, sixteen stories – what difference does it make?

I don’t understand how we can make a telescope that can see these distances. That’s all. I accept the brute fact, because I’m obedient that way, but I can’t get my head around it.

It’s fascinating though. Humans, eh?


  1. says

    Perhaps telescopes at higher elevations are better at circumventing light pollution?

    (I have not seen the program, so I’m just making a random guess.)

  2. says

    Well they are, yes, as are telescopes in the desert – but that doesn’t tell me how they can see across the whole farking universe. It’s just a very basic childish I don’t geddit – how can any tool a human can make see across hundreds of billions of galaxies. It’s too faaaaaaaaaaaaaar.

  3. jehk says

    To be fair the light that’s traveling millions/billions of years is doing most of the work.

  4. says

    What jehk says: The “seeing” is not over any distance at all. The “seeing” is just what happens chemically on a photographic plate, an eye’s retina, or a photoreceptor thingie. The amazing thing is that light left an atom, actually an electron possibly linked to an atom, and headed out into outer space and happen to run into this telescope at just the right place-moment in space-time.

  5. anthrosciguy says

    To be fair the light that’s traveling millions/billions of years is doing most of the work.

    This. Think of it as the telescope only seeing a very short distance, like to its lens or mirror. What it’s doing that’s amazing is making the resultant extremely dim image clear and bright. It’s true that this kind of thing, and a bunch of other clever little things humans have figured out how to do, are pretty wild.

  6. quietmarc says

    I’m probably wrong, but telescopes are basically fancy photon collectors, right? The bigger telescopes have a larger “net” to catch photons and focus them into a picture we can interpret.

    Not sure if it will help, but my current favourite “telescope story” is the story of William Herschel and his sister Caroline as described in the book “The Age of Wonder: How the Romantic Generation Discovered the Beauty and Terror of Science” by Richard Holmes. You probably have a reading list that’s 8 stories tall, but if you’re curious about the first really great big telescope, Herschel’s story is a good one.

    And Caroline, if you’re curious, was a trailblazer for women in the sciences herself and had a very interesting life.

  7. says

    They can look to the edge of the universe – but that doesn’t mean they see much detail that far out. It’s not like they can see the individual stars in far away galaxies, for example.

  8. says

    For some inexplicable reason I’m reminded of Father Dougal’s expression of incomprehension when perspective is explained:

    I’m not sure if it’s available in North America but Manchester’s very own Professor Brian Cox has done two wonderful series, Wonders of the Solar System and Wonders of the Universe. Well worth a view. However, if you are able to watch it you will be thinking ‘that’s too faaaaaaaar’ on a regular basis!

  9. thztds says

    Larger telescopes are better at resolving far away objects due to the diffraction limit.

    I’m not going to go into all the mathematics, but essentially, larger mirrors on telescopes allow you to collect more light and with more light you get better resolution.

    For example, with a 3 inch telescope, two distant stars may blur together into one blob. However with a 12″ telescope, you may be able to collect enough light to resolve them into two distinct spots. For large telescopes, every time you double the size of the mirror, you roughly increase the resolution by a factor of 2. And increasing resolution lets you distinguish between separate objects that are further away.

    I suspect that unless one ends up gaining practical experience dealing with telescopes and optics, this is still something most people will just have to accept that the telescope makers know what they’re doing.

  10. says

    The reason a telescope can see that far is, basically, because light travels that far if nothing gets in the way. Everything else is just details of designing the optics ;-).

    High altitudes are better because there’s less air to muck up the incoming light. (The heat shimmer you see over a sunlit road is just a very big example of the turbulence that’s always going on in the atmosphere). Deserts are better because water vapour absorbs a lot of interesting wavelengths. So high mountain deserts are the best of all, which is why a lot of major ‘scopes are located in the Chilean Andes. And of course, Hubble: no air at all to worry about.

    The reasons ‘scopes are so damn big are 1) you need a big area to collect enough light to make a faint object visible and 2) larger apertures can resolve smaller objects (for reasons that require undergrad math and optics to properly understand).

    The above answers brought to you by some guy with engineering-syllabus training in basic physics, who also used be an amateur astronomer.

  11. Albert Bakker says

    The ‘ bigness’ of the Universe is just beyond human capacity to fathom in any other way than in the abstract. There is no person alive who ‘gets’ this in a direct intuitive sense. Yet now and then an attempt regardless can be wonderfully rewarding. Wallowing for a while in pure ‘wow’ erlebnis expands the mind. Stretching it beyond breaking point is perhaps not as good.

  12. gingerbaker says

    What’s even more difficult to grok is that we really can’t see across to the other side of the Universe, we can only see where the other side of the Universe was 13 (?) billion years ago. The Universe is bigger than that now.

  13. says

    Defraction’s part of it, but usually the main limit is how much light you can collect.

    The farther away a star is, the fainter it looks.

    The bigger the main mirror (or lens) the more photons you get from it, so you’ll need a shorter exposure to take a picture or spectrum. (Think of a bigger funnel collecting rainwater). Or to put it another way, the bigger the main mirror, the fainter the object you can photograph in a given time, before dawn, say.

    Have you seen the Hubble Deep Field? IIRC, that’s a 271 hour exposure, but then the Hubble’s mirror is one metre across. The biggest optical telescope in the world, Gran Telescopio Canarias has a mirror 10.4 metres across, so that’s 108 times the light-collecting area. In theory, it ought to be able to take the same photo in 2.5 hours.

    That’s the point of a stonking huge telescope.

  14. says

    quietmarc, I found a remaindered pb of The Age of Wonder at the local university bookstore just recently, and it’s right at the top of a stack. The 2 Herschels feature in that Nova.

    Hey Geoff that might be someone for the next QED – Richard Holmes. (I have a couple of more longwinded suggestions pending though.)

  15. says

    I was doing some of that in pure ‘wow’ erlebnis while watching. 4 centuries ago Galileo put together that little telescope – and now – [shiver]

    There was a nice bit about the Cassini probe going through a plume that jets out of one of the moons of Saturn and “tasting” it to figure out what it is. Doing so confirmed that the plume is the source of the outermost ring. Very very cool stuff.

  16. Your Name's not Bruce? says

    Another part of the recipe is time. If you point a large telescope at a distant, dim object for a long period of time, you collect more light from that object. With computer imaging techniques several shorter exposures (each of which might still be several hours long) can be combined to produce a single image that is better than any of the single images. The Hubble Deep Field and Ultra Deep Field images were produced in this way.

  17. MyaR says

    What gingerbaker said. I get most of the optics part (having photography as a hobby helps), but the timescale that goes with the distance is the part that boggles my mind. How can the light just keep going for billions of years? Because that’s what light does, I guess.

  18. says

    Any and all suggestions for the next QED will be gratefully accepted. We do think we need to get someone from the particle physics/astronomy side of things

  19. agenoria says

    There’s a transcript on the programme’s website (don’t see many of those – it’s very useful!):

    Giant doors, eight stories high, slide apart. These twin eyes are preparing to look into deepest space. They belong to the Large Binocular Telescope.

    It is one of the most powerful telescopes on Earth, costing over one hundred and twenty million dollars. These 28-foot wide mirrors collect light from objects millions of times fainter than anything our eyes can see. Six-hundred tons of machinery turn the mirrors to look more than 13 billion light-years away, to the very edges of the visible universe.

    The second to last word is important: “visible”. It’s not claiming to see the whole universe, just that part from which there has been time for the light to reach us. And the light keeps moving until something stops it.

  20. justsomeguy says

    Sometimes I wonder about what a religious experience feels like, and if it’s similar to the sensation of a boggled mind I get when I think about big astronomical phenomena. Take the Hubble Deep Field images, for example: our planet *did not exist* when some of these photons started their journey. Not only is that an incredible distance to travel, but it makes me wonder what sort of history was experienced by these galaxies, each with countless stars and unimaginable potential for planets. I feel a combination of utter insignificance (at our place in the grand scheme of the cosmos) and immense pride (at what our incredibly unlikely species has been able to accomplish in an incredibly short time). Is this similar to what a religious person feels when they contemplate the place of humanity in comparison to their deity of choice?

  21. como says

    It is certainly fascinating. I think that it is more accurate to say that these larger telescopes see “clearer” rather than “farther”. After all, we constantly receive all of this light both near and far, but only those scopes with the biggest lenses can discern the very faint galaxies at these distances of quadrillions of miles.

    Bigger telescopes are better because the bigger the lens, the more light it can detect and focus. Also, the gathering capability increases exponentially based on this bigger size: If your telescope’s lens is 4 times wider than mine, yours gets 16 times more light and therefore sees that much clearer.

    Hope this helps!

  22. says

    I often find that journalistic excess undermines rather than enhances my sense of wonder. That we can build instruments to so dramatically extend the capacity of our senses is indeed wonderful, but that “edge of the visible universe” bit is just typical journalistic sensationalization of the trivial.

    You, unaided, can “see” to the edge of the visible universe in the sense that occasionally a photon from out there excites one of the rods in your retina. Of course, you see with less detail than the telescope, but even it can’t read the label on jar of peanut butter out there. What is relevant is how much more detail it can see than you can, and the key sentence is “These 28-foot wide mirrors collect light from objects millions of times fainter than anything our eyes can see”. This is wonderful but not surprising when you consider that the area of your pupils is less than 1/4 square inch and the number of square inches in the area of the telescope’s mirror is about 3 times (28 times 12)squared – which is indeed about a million times the area of your pupils.

  23. says

    Well and I can see to the edge of the visible universe just by looking up – that’s what’s visible to me, so there I am seeing to the edge of it. Heh.

    But seriously, edifying comment, and now I do get it. Nova: more of that kind of thing please.

    I’m glad I asked.

  24. Matt Penfold says

    Can I just confuse things by adding that not only does the size of the individual mirror of a telescope matter when it comes to resolution, you can also use telescopes that are physically separated and use clever computerised algorithms to amalgamate their images into a single image that can have better resolution than any of the single telescopes used to form the image.

  25. lorn says

    Well … I’m surprised I have to explain it to you … but, heregoes … boys have a thing about penis size and they automatically associate the size of their toys with this. So if he said that his dick was so big he had a eight story zipper you would know what he’s talking about.

    Glad I could clear that up for you.

    So just remember that when someone brags about the size of the doors they are talking about the size of the telescope, and when they are talking about the size of their telescope, or gun, or house house, or how fast their car is, they are talking about the size of their penis.

  26. pensnest says

    I can’t get my head around that kind of thing, either. I find it fascinating to read about the incredible things astronomers and physicists can discover, but the *scale* of it is just beyond my mind’s capacity to wrap around. Likewise the bizarre world of quantum physics. My mind can deal with a scale of “bacteria to the solar system”, more or less, but go much beyond that in either direction and I just end up feeling like a flopping goldfish.

    I’m glad we have physicists, and astronomers, and their like. I just think their brains must work in quite another way to my own.

  27. Chris Lawson says


    You can see a lot of the universe without a telescope. The farthest galaxy reportedly seen by the naked eye is M83 which is nearly 15 million light-years away. (There is some skepticism about this claim, though; the closest unambiguous naked-eye galaxy is Bode’s galaxy, at 12 Mly.) But there was a naked-eye supernova (GRB 080319B) in 2008 that was 7.5 billion light-years away.

    It gets even better. Google “Olber’s paradox” for more details, but if the current Big Bang + inflation theories are correct then the dark spaces in the night sky* are actually vastly red-shifted light from extremely distant parts of the universe. You could say that the blackness of the night sky is a naked-eye experience of the universe from when it was only 300,000 years old.

    *Except for the dark spaces in the band of the Milky Way — they’re caused by dust clouds blocking light from the galactic centre.

  28. Erp says


    Actually Laura Bassi predates Caroline. She was appointed professor at the University of Bologna in 1732 at the age of 21 and eventually became chair of experimental physics (1776 until her death in 1778).

  29. bad Jim says

    The newest telescopes have adaptive optics so they can actually change their curvature to compensate for atmospheric turbulence, producing images that rival the clarity of telescopes in space. Astronomers also finally realized that the equator was the best place to site observatories, since there they could observe nearly the entire sky.

    A few months ago the local classical station played one of William Herschel’s symphonies, which was really rather nice. It was too bad that he was a contemporary of Haydn and Mozart, whose brilliance eclipsed his considerable talent. He was the first person in history to discover a new planet, though, so he’ll never be forgotten.

  30. TV200 says

    Gonna third the recommendation for the BBC “Wonders” series with Brian Cox. When the rebooted “Cosmos” was announced, I thought, “Well, they already made it”. His enthusiasm is infectious. It is available on disc in the US.

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