Wikijunior:How Things Work/Telescope

Who invented it?
Hans Lippershey was a German-Dutch eyeglass maker who is believed to the inventor of the telescope as he tried to patent it in 1608, in his patent he claimed it was "for seeing things far away as if they were nearby", but some believe that he was not the first person to make a telescope, he also did not get the patent, since other eyeglass makers also discovered how to make a telescope, this kind of telescope uses lenses and is called a refracting telescope or refractor for short.

It's not really known how Lipperhey actually discovered how to make a telescope, one legend says that he did not discover it himself but some children in his shop who were playing with lenses, finding out that a distant weather vane appeared closer if viewed through two lenses, others believe that Lipperhey copied the design.

The reason why early telescopes were discovered by eyeglass makers is because they had experience working with lenses and optics.

Lipperhey did not call it the telescope however, he called it the "Dutch Perspective Glass" the word telescope wasn't coined until three years later by a scientist named Giovanni Demisiani.

These early telescopes also did not have a lot of power, the power of a telescope is how near it can make far away things look, early telescopes only had a power of about 3x, meaning that a far away object will only look 3x bigger, that's not a lot, due to how they worked, the image was also upside down.

Galileo Galilei was the first scientist to improve and work on telescopes, his first attempts weren't very powerful, but he eventually made a telescope with 30x power, he also found out how to make the image the right way up, by using a concave eyepiece and not a convex one, it was good enough for him to observe the moon with, and he also sold them, they were popular among sailors.

How dangerous is it?
Most things are safe to look at through them, but NEVER look at the sun or another bright object through a telescope, doing so can damage your eyes.

Using a telescope to look inside someones house and spy on them is against the law.

Bigger telescopes are really heavy so don't drop them.

Always put caps on your telescope and keep it away from windows when your not using it, as they can focus the sun and start a fire.

The lenses or mirrors are made of glass and glass can be really sharp when broken.

What does it do?
It makes things that are far away look closer, a good telescope may also make it brighter.

How does it vary?
Some use mirrors, these are called reflecting telescopes, they are popular with amateur astronomers, some telescopes use lenses, these are called refracting telescopes, the kind covered in this article, some telescopes use both lenses and mirrors, these are called catadioptric (cat-a-die-op-trick) telescopes.

A small collapsible refractor for looking at distant objects on land is called a spyglass or terrestrial telescope, it's what pirates are said to use.

A really small refracting telescope with a low power like 8x that can fit in your hand is called a monocular.

Two refracting telescopes connected to each other are called binoculars, unlike a monocular telescope, it allows you to see depth as it uses both eyes.

Telescopes for looking at the night sky are usually on a tripod stand and something called a mount, which lets the telescope move or "look around" this is because astronomical telescopes are so powerful that you cannot hold one because your natural shakiness will make the image look really shaky.

The most common kind of telescope mount is the altitude-azimuth, it lets the telescope pan left and right, and tilt up and down.

How has it changed the world?
The telescope changed in the world in the fact that there's nothing else like it when you need one, a telescope or binoculars is the first thing you look for when you see something strange in the distance, they were used on sea before binoculars were invented to see distant objects.

Telescopes let people watch dangerous things from a safe distance as if they were next to it, this is very useful for scientific research of dangerous things like explosions.

Some camera lenses are like telescopes, they are called telephoto lenses, they are used by sports and wildlife photographers to make subjects look very close in pictures.

Telescopes are sometimes attached to guns to make shooting distant objects easier, telescopes are also used by surveyors, with something called a crosshair, a telescope can be precisely pointed to a small object in the distance, the telescopes used by surveyors are called theodolites (thee-odd-o-lights) they measure angles on a precisely graduated mount, the telescope makes them very accurate and easy to use to sight distant targets.

The field which telescopes changed the most is astronomy, early astronomers just looked at the sky with their own eyes, but powerful telescopes let us see distant planets and other celestrial objects, these telescopes can be very big, some huge telescopes are even sent into space, such as the Hubble space telescope, there are even radio telescopes, which make an image out of radio waves.

How does it work?
The principle behind the refracting telescope is actually so simple you can make one yourself with a few pieces, early refracting telescopes usually had no less then 3 or 4 pieces.

Refracting telescopes work by bending light, called refraction, with glass lenses, the light is bent or focused to a single point.

In a simple refracting telescope, there are two lenses:

The lens at the front, or the objective, is a big lens whose purpose is to gather light and focus it to a point, it's optical power and diameter can determine how zoomed in the image is going to be, the image from this lens is focused to a point but is not viewable by the human eye, it needs something else to focus onto and that's what the eyepiece is for.

So named because it's the lens you look through to use the telescope, it's smaller then the objective lens, this is because both lenses have to be different sizes, or the image will not be magnified, the properties of the eyepiece also affect the image, this is why high end telescopes allow the user to swap in different eyepieces, to make the image bigger, smaller, brighter or darker depending on application.

The objective lens is mounted at the end of a tube matching the diameter of the lens, in the back of this tube is inserted another tube containing the eyepiece, so the eyepiece tube can be pulled in and out, this is because the telescope needs to be focused for a clear image of what is to be viewed through it, that is the eyepiece needs to be on or around the focal point of the objective for a clear image to form.

The view through this kind of simple telescope is always upside down, this is because the light coming through the top of the objective gets bent downwards and reaches the bottom of the eyepiece, and the light from the bottom of the objective gets bent upward and reaches the top of the eyepiece, this is usually corrected by putting a special prism in the telescope tube, or using an eyepiece which has a negative optical power, these are usually concave, as opposed to standard lenses which are convex (outward).

Refracting telescopes can be very complex and expensive, using more then one lens to make the image look clearer and less-prone to a rainbow effect seen on the edges of bright objects.

Refracting telescopes reached their peak in the 1890s but now are rarely used for astronomical purposes in favor of reflecting telescopes.

What idea(s) and/or inventions had to be developed before it could be created?
Optics and lenses, Optics is the study of how light acts and behaves, lenses are pieces of glass that focus light to a single point.