A Brief Guide On How Telescopes Work

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For a very long time, we used our eyes to gaze up at the beautiful sky. We saw tiny sparkling lights which we named stars, a moon, and a sun. But Galileo was curious to know if there was anything else up there we couldn’t reach with our naked eyes?

Then came one of the most significant inventions of history – a telescope. This article will bring you the answer to the question – how telescopes work?

What Is A Telescope?

Before beginning with the guide on how do telescopes work, let us first understand what exactly the device is.

The sky is enormous, and there are oodles of objects in it that are hard to see with naked eyes. That is because they are very far away. Telescopes are the tools that help magnify those far away objects and make it easier for us to see them.

Why Do We Need A Telescope?

To better understand how telescopes work, we must first know why our naked eyes can not see the distant objects in the sky.

The Retina in our eyes is called the ‘eye screen.’ Any object that does not take up enough space on this screen appears either blurred or completely invisible to us. A bigger screen can take up more light from the object and create a clearer image for us.

A telescope helps us do exactly that. Once we have a brighter image, we can magnify the desired part of that image so that it stretches out over more pixels on our retina.

How Do Telescopes Work?

Now that we know what they do let us find out how telescopes work.

All telescopes have two main pieces that make them do what they do. 

  1. There is an Objective lens in the refracting telescopes, and a primary mirror in the reflecting telescopes. These pieces collect lots of light from the distant object and bring it to a point called ‘focus.’
  2. Both types of telescopes have an eyepiece lens that takes the light from the focus and magnifies it into an image. This image then takes up a large portion of our retina.

Every telescope has two main properties. 

1. Ability to collect maximum light. 

This property depends directly on the aperture ( the diameter ) of the lens or the mirror used to make the telescope. The larger the aperture, the more the light the telescope collects and sends to the focus. And the brighter is the final image.

2. Ability to magnify the image.

This property depends on the combination of lenses used to make the telescope. However, any eyepiece can be used to create an image from the light. Thus, the aperture is a more significant property of the telescope.

How Does A Refracting Telescope Work?

Refracting telescopes are the ones we are most familiar with. They are made up of the following parts. 

  • A long plastic or metal tube
  • A combination of lenses at the front end ( the objective lens )
  • Another combination of lenses ( the eyepiece)

The tube is supposed to hold these combinations of lenses in place at perfect distances from each other. It also keeps the lenses safe from dust and other dirt that might interfere in the formation of a good image.

The objective lens gathers light from the object and bends or refracts it to the focus point near the back of the tube. Then the eyepiece projects the image on our eye. It spreads the light out and creates a magnified image.

Eyepieces have shorter focal lengths than the objective lenses.

Refracting telescopes create high-resolution images, enough to see the details in planets and stars. Despite this, a refracting telescope is not suitable for observing deep, faint sky objects like galaxies. It is because the aperture of the objective lens is limited. 

Refracting telescopes are also relatively more expensive than the other types of scopes. 

How Does A Reflecting Telescope Work?

Reflecting Telescopes are preferred over the refractors due to the chromatic aberration problems caused by the lens in the refractors. A mirror does not cause such problems.

A reflecting telescope is made up of a similar tube than that of a refractor. In place of the objective lens, a reflector uses a thin, perfectly curved mirror. The light concentrates by bouncing off the mirror.

A secondary mirror is placed in the focal path of the primary mirror that reflects the light out the side of the tube to the eyepiece. The secondary mirror is so tiny in size as compared to the primary mirror that it does not block any image.

Mirrors are lighter than lenses. This property of mirrors makes it easier to launch them into space. They are also one-sided, which makes them easier to clean and polish. Even a large-sized mirror does not have to be thick.

Among all these benefits of the reflecting telescope over the refracting telescope, there are also many disadvantages.

  • Spherical Aberration – Light reflected from the edge of the primary mirror gets focused to a slightly different point than that reflected from its center. The reason for this is the mirror’s curved shape. This causes an unclear image formation.
  • Astigmatism – The mirror is slightly egg-shaped. So, the star images focus on crosses rather than points.
  • Inversion – Curved mirrors are like spoons. The images are inverted either upside down or from left to right. 

Also, there is a significant loss of light while using reflecting telescopes. This is due to the fact that no reflective coating for a mirror returns 100 percent of the light striking it. The best it can do is return 90 percent of it.

Gaze Into Space

We hope that this article gave you a clear and brief knowledge of how telescopes work.

You can make your own telescopes as well. A Dobsonian telescope is a Newtonian reflecting telescope that has alt-azimuth mounting. It is inexpensive and easy to build at home.

With the advancement in technology, scientists have come up with the kind of telescopes that can create images of more than just visible light. This means that the computerized telescopes can capture images of objects that do not emit any light and are, hence, almost invisible. It is astonishing to know that even after years of research and revelations, there is a lot more in space that we don’t know about yet.

Now that you know how does a telescope work, get a good telescope for yourself, or build one of your own.  Gaze into space, and have fun!