Since the early 1600s, telescopes have been the toolbox staple of the stargazer. Used to pick out craters on the moon, the shapes of distant galaxies and spy on the neighbors foolish enough to leave their curtains open.

But if you've ever wondered what kind of sorcery could conjure a perfectly crisp image inside a tiny tube When all your eyes can make out is a Wibbly smudge, then this is the article for you.

For you to understand how telescopes work? We first need to understand why there's a limit to what we can see with the naked eye. When something is further away, it is smaller thanks to perspective, and it also gets darker, eventually getting to the point where there's just not enough light bouncing off that object and reaching our eyes. So, better long-distance viewing relies on two things, gathering as much light as possible and the increasingly apparent size of the distant object. One way of doing that is using lenses, curved pieces of glass that refract light. That bend it as it passes from air into denser glass.

The first telescope was constructed around 1608, by a Dutch spectacle maker called Hans Lippershey. It consisted of two lenses aligned with each other, capable of magnifying objects up to three times.



 Light, traveling from a distant object, comes at us in parallel rays. When these rays enter the objective lens.



 That's the one facing the object.




They refract and because that objective lens has a bulging shape, it's convex: those light rays are bent towards each other. Inside the tube, these light rays converge until they meet at a focal point before then diverging out again.

The thing is with those light rays crossing over each other the image is now upside down it's not to worry though because when you're looking at space it's not really an up or down so doesn't particularly matter.

Now the eyepiece lens, which I think you'll agree the rather apt name for the lens closest to the eye, takes the now diverging light rays and straighten them out again, creating a virtual image on your retina.



As the virtual image is closer to your eye than the real object, it has the effect of magnifying the image, tricking the eye into thinking the object is closer than it really is.

The amount of light a telescope can gather depends on the size of the objective lens and there are obvious practical limitations on how big you can make a giant lump of glass. The largest permanent refracting telescope was installed at the Yerkes Observatory in Wisconsin in 1897, and it has an objective lens over one meter in diameter. It weighs in at around 26 tonnes. So unfortunately it's one of those cases where bigger isn't necessarily better. Refractor lenses suffer from the problem of lost light. Some like that should pass through the lens actually bounce off it, just like when you see your reflection in the window. Not ideal when you're trying to pick out dim, distant stars.

 So, the bigger you take the telescope and the lens, the more light escapes. The solution to this problem there was the invention of the reflector telescope. Instead of bending the light with a huge glass lens like a refractor telescope does. A reflector telescope uses vast curved mirrors of different techniques, but pretty much the same principle. Rather than a convex lens, which the refractor telescope uses. Use a concave mirror to receive the light from whatever it's being pointed at. The bold shape of this mirror reflects the parallel light rays and angels. So, they'll converge at the focal point before then diverging back out again. Most reflector telescopes then have a secondary mirror to deflect the image sideways so you don't have to put your face in front of the mirror, which of course would get in the way of the actual object.





 Finally, an eyepiece lens magnifies the image, just as with the refractor telescope. Using a mirror lightness gets around the problem of unwanted light reflections because all the light should be reflected however just as with refractors to get a lot of light you need a really big mirror.

The good news though is that it's much easier to make a massive mirror than it is to make a massive lens. Mirrors simply have to be silvered reflective surfaces. They don't even have to be a continuous smooth curve.

The largest reflector telescope currently in operation is the Gran Telescopio Canarias in Las Parma. Which has a mirror that's made of 36 hexagonal segments is a whopping 10.4 (ten-point four) meters in diameter.

That's not the end of the story for reflector telescopes though, so successful in these giant mirrors that at least three more are currently under construction. Among them is the imaginatively named Thirty-meter telescope and there are no prizes to guessing how big that one will be, and these superbly named European extremely large telescope, I guess they're thirty-nine point three-meter telescopes didn't really have the same ring to them.

They're a regardless of how big the mirror or lens on a telescope is. Any scope on the ground will suffer the effects of atmospheric distortion, which can make any image of the stars look wibbly-wobbly. Oh, that's not the scientific term, that's just a Greek term. It is an atmospheric distortion, that makes stars appear to twinkle when you look at them with your naked eye, and to avoid it most research telescopes have popped on the top of mountains where the air is thinner and there's a lot less light pollution.

There's one surefire way of avoiding atmospheric distortion and that's to remove the atmosphere altogether, by launching a telescope up into the vacuum of space. Knowing that the almost vacuum of space light from other stars or the light that gets reflected off planets can travel undisturbed to the telescope. The Hubble Space Telescope it's launched in 1990, is the most famous of these.




 It's a reflector telescope, and it's produced some of the most memorable images of distant galaxies and nebulas and get this outside of the haze of the atmosphere it's able to pick out objects with an accuracy equivalent to seeing a firefly in Tokyo from New York City. Before I wrap this up then aware, I've only talked about optical telescopes, those that collect and magnify visible light just like our eyes do. There is a whole range of other ways to observe distant objects. For instance, there's the Spitzer Space Telescope, which's equipped with infrared cameras that monitor heat sources out in the depths of space, and the Kepler telescope, which keeps a watchful eye on over 100,000 stars at once, using sensitive visible light photometers to try to detect the passage of planets.

It's fair to say that the simple act of seeing far has come on leaps and bounds in the last 400 years. We've gone from a crude, three times magnification to be able to see unbelievable distances in remarkable detail.

Personally, I'm looking forward to the next 400 years of insightful telescope names. I'm rooting for the unthinkably vast telescope, or perhaps the fantastically accurate reflector telescope. You can work out the acronym for that one yourself.