The Newtonian telescope: how does it work?

Newton’s reflector telescope, also known as the Newtonian telescope, is the most ancient known reflector telescope. As its name indicates, it was developed by the British scientist Isaac Newton, and it was built in 1668. This type of telescope uses a primary concave mirror and a diagonal plane secondary mirror.

This simple yet effective design makes it very popular among the manufacturers of amateur telescopes. Nowadays these telescopes are found under various models, and sometimes incorporate additional optical elements in order to improve certain aspects of their functioning.

How does it work?

All existent telescopes work under the same principle: they capture the light of distant objects and amplify it to form an image. However, each telescope uses a different technique to obtain an image of objects that are far away. This is a scheme of the functioning of the Newtonian telescope:

In the first place, light enters by the upper part (the left) of the tube of the telescope. At the lower part is situated a primary mirror that can have either a parabolic or spherical form. Initially, Newton created the mirrors by himself using an alloy of copper and tin.

The light captured by the primary mirror is then reflected in the direction of the secondary mirror. The latter is a plane mirror at the upper part of the tube of the telescope that reflects light at an angle of 90º. This means that light is directed towards the side of the tube, where the eyepiece is situated.

The magnification and focus of light take place inside the eyepiece.

New telescopes

For more than 300 years, when the first telescopes began to be fabricated, there have been many advances that have allowed the construction of increasingly big telescopes. We nowadays have telescopes (such as the Hubble or the James Webb) that are in orbit, telescopes with mirrors tens of metres in size, and other ones that observe in different wavelengths (different types of light).

At present time, the telescope that Newton manufactured and which was a great invention for the epoch, is one of the most used telescopes in amateur astronomic observations.

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