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Introduction to Telescopes


Humans have been studying the night sky since the beginning of time. Different civilizations had their own beliefs and their own way of mapping the stars in the sky. They would build large structures and monuments that would line up with the stars at certain times of the year. These were their calendars. They followed the stars and the moon like clockwork.

As time went on, one theory about the night sky became widely accepted. The thought was that the Earth lay inside a glass sphere or ball, and that the stars were simply holes in that ball through which light from the heavens could pass.

Ancient ideas about astronomy were very different from what we know today

Ancient ideas about astronomy were very different from what we know today

It wasn’t until the invention of the telescope near the beginning of the 17th century (1600s) that this belief came tumbling down when, in 1609, a scientist by the name of Galileo Galilei first peered through his small homemade telescope at the stars. Since the invention of this amazing instrument, our knowledge of the heavens has grown by leaps and bounds.

The first telescopes used to peer into space were refracting telescopes. This means that you would look straight through the telescope from one lens to the other through to the image you were looking at. During the first few decades after refracting telescopes were invented, the race was on for the best telescopes.

Galileo Galilei

Galileo Galilei

However, the lenses used in these telescopes were not the best. The art of grinding and polishing glass lenses was slow going in the beginning. The images seen through refracting telescopes were not perfect. Because of the way the lenses bent the light, the images were always a little blurry. This blurriness is called chromatic aberration.

It was soon discovered that if the telescope lenses were further apart, they would show a clearer image. The distance between the lenses is called the focal length. Telescopes began to get really, really long. A well-known telescope was made by Johannes Hevelius. His telescope had a focal length of 158 feet (48m). As you can imagine, these really long telescopes were very hard to work with. They were very difficult to move and set up.

In the 1680s, Isaac Newton invented the reflecting telescope. This type of telescope had a mirror inside that would reflect the image to a focus point. Newton found that this made the images of space much clearer to the viewer.

A drawing of Johannes Hevelius' very long telescope

Johannes Hevelius’ 158 foot long telescope.

Isaac Newton's notes about his new reflecting telescope

A diagram of Isaac Newton’s reflecting telescope.

Isaac Newton's reflectin telescope was much smaller than the refractory telescopes of the day

Isaac Newton’s telescope.

Since that time, humans have raced to build bigger and better telescopes. The bigger a telescope is, the more detail it reveals in distant objects, and thus the more we can learn about them. Eventually humans were able to launch telescopes into space that allowed even more detailed looks at objects in space, like the Hubble Space Telescope.

Very large telescopes are used today to study the stars

Large modern telescope.

Nowadays, there are many different types of telescopes astronomers use to study space. There are radio telescopes, x-ray telescopes, infrared telescopes, gamma ray telescopes and ultraviolet telescopes.

Did you know?

Scientists can take two or more telescopes and use them together acting like one giant telescope to get a better image. This is called an interferometer. An interferometer has the same power as would a telescope the size of the distance between the telescopes being used.