I do not understand how the Hubble Space telescope can get pictures of galaxies billions of light years away and for them to be detailed… It doesn’t feel real. Why are our cameras only able captures so much? How are we able to see light years away… explain like I’m 5.
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Telescopes have large mirrors that focus and magnify light from an object. The longer those mirrors are pointed at a distant dim object the more light is collected and brighter, more detailed the object appears.
Well on the most basic level, big camera= big lense big lense = better picture.
The hubble telescope has an extremely large lense.
So if it were possible for you to walk around with the HST in your pocket, you’d have some mighty fine pictures as well.
As you said, galaxies are very far – light years away! There’s two main things that help us see these distant things.
1. The things we’re looking at that far away (glaxies and nebulas) are also really REALLY big. For example, even though it’s 2.5 million light years away, here’s the [actual accurate size of the Andromeda galaxy in our sky](http://i.imgur.com/EpuhHJa.png). If it were bright enough to see with the naked eye, that’s how it would look right now. It’s *not* that bright, but it’s not exactly small either – it takes up more of the sky than the moon even though it’s millions of times farther away! So don’t think that “light years away = tiny minute speck”
2. So how do we see things to dim to see with our eyes, like Andromeda? Well, do you know how you can use a magnifying glass to concentrate sunlight into a smaller and much brighter spot? Big telescopes do the same thing. What makes the big telescopes “big” is a [giant mirror (or array of mirrors)](https://media.npr.org/assets/img/2013/08/24/gmt-1-hi-res-e884e0fb05a54d4557cfb1e96e0444b3ab72d35f-s1100-c50.jpg). All that mirror is doing is collecting light from that whole big surface and reflecting it onto a very small spot where they put a detector like what’s in a regular camera. With the brightness turned up, the telescope can “see” dimmer things. Boom, [Andromeda.](https://upload.wikimedia.org/wikipedia/commons/5/57/M31bobo.jpg)
Even though light from billions of light-years away is very faint, the light just keeps going straight until it hits something. Since Hubble is in space, it can focus on a spot and gather light over extended periods without dealing with external vibrations or light-scattering particles. On Earth, there are always ground vibrations, air vibrations (sound), wind, water vapor, dust, or even just air that scatters the light.
The general way any camera works is that there’s some piece of equipment that is sensitive to light. Early cameras used film, which is coated in a light-sensitive chemical that changes when exposed to light, which could be sent through a chemical development process that creates a visible photograph. Modern cameras use special microchips that generate electrical signals when light shines on them that a computer can measure and record as an image data file.
If you want a camera that takes pictures in fine detail, you want something that’s ultra, ultra sensitive. That’s point number 1 to Hubble. Hubble was built in the 80’s, but even so, its equipment is significantly more sensitive to light that even today’s best iPhones. Though it’s a pretty unfair comparison since they aren’t really built for the same jobs, and they don’t even take the same kinds of photos. Still, Hubble’s camera equipment is one-of-a-kind, the best thing money at the time could buy, while your cell phone camera, advanced and worthy of engineering praise it may be in its own right, is designed to be mass-manufactured and purchaseable by middle class workers.
The next thing Hubble has up its sleeve is that it’s focused on an *extremely tiny* point on the sky. It is, after all, a telescope. You’re not going to be taking selfies with the thing. Your camera, by contrast, is likely designed to capture entire landscapes and people, so it captures light from a broad view. Though you could make it work a bit more like Hubble if you, say, put your camera lens directly up against the eyepiece of a backyard telescope. Amateur astronomers do this all the time and telescopes are often made with special attachment fixtures just for this purpose.
Lastly, and probably most importantly of all, Hubble simply collects more light than your camera can. Light streaming into your camera to be recorded by the sensor is like rain pouring into a bucket. The more rain you collect, the more you’ll fill your bucket. Or in this case, the more light you collect, the brighter and sharper your image will be. Your camera is likely designed to capture daytime footage of normal day-to-day activity in full sunlight. That’s really bright. Your camera’s sensor will be completely overwhelmed if it was left exposed for any longer than a split second. That’s why cameras here have shutters that make the “click” sound (at least they used to, nowadays the click sound is faked). It very briefly opens up a little window that lets light from the scene strike your sensor, before rapidly shutting it off again. Since it’s so tuned to receiving lots of light most of the time, it can be very difficult for it to pick up very faint scenes. This is why consumer cameras often have very crummy night mode performance. Have you ever tried taking a photo of the night sky, or tried filming a fireworks show? If you’re lucky, it will probably look like shit. If you’re unlucky, it won’t look like anything at all. Hubble’s camera is way different. It’s designed to capture *very* faint signals. We’re talking a couple individual photons every few minutes faint. In the rain analogy, this would be like if only a couple tiny, barely noticeable drops were falling every few seconds. Hubble compensates for this lack of light by having a MASSIVE mirror that collects light across a large area, and focuses it all down onto its sensor, like a giant rain-collecting funnel. The size of this mirror can’t be understated–if you stood it up next to yourself, it would be [taller than you are](https://www.taschen.com/media/images/1640/205a_hubble_space_telescope_fo_01134_1505221247_id_965873.jpg). Compare this to the light-collecting area of your phone camera lens, which is the diameter of the center hole of a Cheerio.
Hubble’s successor, the James Webb Space Telescope, was just launched last Christmas, and has only a few days ago successfully deployed. Its mirror is [even bigger](https://upload.wikimedia.org/wikipedia/commons/thumb/4/42/JWST-HST-primary-mirrors.svg/640px-JWST-HST-primary-mirrors.svg.png) than Hubble’s, thus, it has significantly more resolving power. Though, due to a quirk in what kind of light Webb is looking for compared to Hubble, it isn’t going to be quite as big of a leap forward as it may initially appear.
1) It captures lots of different wavelengths of radiation, much of which isn’t visible to us. That makes it much more effective than our eyes, and normal cameras.
2) It has enormous and near flawless lenses to capture the most radiation possible, and specialised sensors and processing to maximise the data captured from that radiation.
3) It takes photos of REALLY BIG STUFF. Very far away, but also huge. A galaxy can have a trillion stars in it, no problem. So even tho it’s very far away, it still generates a lot of radiation.
ELI 5 version. Squint your eyes…and allow them to only permit the slightest amount of light in. Then open them up REALLY wide! That’s what hubble is…a very wide opening…in a very dark location – so it is able to collect more usable photons. Remember, light consists of all wavelengths, not just the ones we can see (visible light). You have detectors (rods and cones, eye cells) which are disturbed or excited by photons hitting them. Only hit one cell and you haven’t got much of an image – just a flash. Consider this: If you travel in to space out to around Neptune you’d no longer be able to see the sun…its light would flash because your eye cell detectors need about 9 photons per millisecond to be excited enough. That light energy is still hitting your eye but you cannot ‘see’ it. With hubble, it’s up in space, NOT looking at the sun (so basically it’s in darkness – except for the minimal amount of light reflected from planets, moons, asteroids and other gas/dust). Suffice to say that it’s looking into darkness for a very long time to allow those photons to hit the detectors and collect. Remember, Hubble isn’t using eyes to see, but detectors which are much more sensitive. Like, here’s an example. To guage the distance from earth to the moon, scientists shoot a laser at the moon – which, of course, that light gets scattered by the atmosphere both going out and returning. It reflects off of a retro-reflector left on the moon during one of the trips. And they’re able to time that trip and calculate the distance. Guess how many photons make it back to the detectors? About 25. You get enough photons hitting the detectors enough to excite them…as well as excite the nearby detectors (ultimately a LOT of detectors need to be hit – think along the lines of pixels on your monitor…each a single blip of light at a certain color – all forming a picture). But to capture these images it has to stare at the same spot, then move EVER so slightly and stare at the next spot…ultimately the images it generates is a mosaic of ‘stared at spots’ all stitched back together. Technically every image you see is a mosaic of excited eye cells at differing wavelengths that our brain interprets into images. Scientists then take those images, makes sure they’re lined up properly to generate the final images of what you see. Hubble has mirrors which reflect and concentrate a larger opening (aperture) and focus it down to the detector. Remember, photons are very small…and like a movie projector can spread them out to a huge screen, so can a huge mirror focus them down for a clearer image…or thousands of separate images stitched back together as one.
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