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Physics for Kids


A telescope is an instrument used to see objects that are far away. Telescopes are often used to view the planets and stars. Some of the same optical technology that is used in telescopes is also used to make binoculars and cameras.

Important properties of Telescopes

The two most important properties of a telescope are:
  1. Light gathering ability - The better a telescope can gather light, the better you will be able to see far away stars and faint objects in the night sky. This feature is usually determined by the size of the aperture of the telescope. The larger the aperture, the more light the telescope can gather.
  2. Magnification - The magnification of a telescope describes how much larger the telescope can make objects appear.
Lenses and Mirrors

There are two main types of telescopes. One type uses lenses to magnify the image. Telescopes that use lenses are called refracting telescopes. The other type uses mirrors to focus the light of the image. These telescopes are called reflecting telescopes.

Refracting Telescopes

Refracting telescopes use lenses to bend the light to a specific focal point such that the object will be magnified to the viewer. You can go here to learn more about the refraction of light using lenses.

The basic refracting telescope has two lenses. The first lens is called the objective lens. This lens is a convex lens that bends the incoming light rays to a focal point within the telescope. The second lens is called the eyepiece. This lens takes the light from the focal point and spreads it out across the retina of your eye. This makes the object seem much closer than it really is.

Reflecting Telescopes

Reflecting telescopes use mirrors instead of lenses to focus the light. A concave mirror is used to gather light and reflect it back to a focal point. In order to get the light out of the telescope, another mirror is used to direct the light to an eyepiece. There are various designs of reflecting telescopes, but the original design by Isaac Newton is still popular today.

Example of a Newtonian reflecting telescope

History of the Telescope

The first telescope invented was a refractor invented by Dutch lensmaker Hans Lippershey in 1608. Galileo made some improvements and first used the telescope for astronomy. The refractor was further improved by astronomer Johannes Kepler around 1611. Kepler used a convex lens for the eyepiece. Although this made the image appear upside down, it improved the usability of the telescope.

In the late 1600s, Isaac Newton developed the reflecting telescope. By using mirrors instead of lenses, Newton was able to make an improved telescope that did not suffer from some of the issues with the refractor such as chromatic aberration.

The Hubble Space Telescope

One of the most famous telescopes in the world today is the Hubble Space Telescope. This telescope was put into orbit around the Earth in 1990 by the Space Shuttle. Being outside the Earth's atmosphere allows the Hubble to view outer space without background light. This has enabled it to take some amazing pictures of far away stars and galaxies.

Hubble Space Telescope above the Earth
Hubble Space Telescope
was the first space-based telescope.
Source: NASA.

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