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Last updated date: 16th Jul 2024
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Introduction to Telescopes

Most of us might have been left awestruck looking up at the starry sky and the moon. Stars, planets, the moon, etc. have always been a fascination for human beings since ancient times, and hence, humans have since shown a keen interest in knowing more about these areas. 

Looking at the Sky Using Telescope

Looking at the Sky Using Telescope

As a result, scientists started inventing different tools for observing celestial objects, and the telescope is one of them. It is said that people in ancient India used telescope-like instruments for observing celestial objects and that was about 900 years ago.

What is a Telescope?

A telescope is an optical instrument consisting of a particular arrangement of curved mirrors and lenses in such a way to make faraway objects appear nearer. 

Functions of a Telescope

  • For Observing Celestial Bodies From Earth’s Surface

Telescopes are used by both professionals and non-professionals for observing celestial objects.

  • For Accurate Data Collection

An instrument known as Hubble Space Telescope (HST), which was located in the earth’s orbit, is the best-known optical telescope that collected data for the deep universe.

  • For Analyzing Image and Light

The first and foremost purpose of a telescope is to provide graphical representations of distant objects.

How Does Telescope Work?

Telescopes usually work by collecting and focussing light from the night sky with the help of curved mirrors or lenses. The big lens collects the light from the source while the small lens brings the image of that object to our eyes.

Refracting Telescopes

Refracting telescopes, also known as refractors, use a lens as their objective to form an image. It forms a clearer and brighter image of the object to the viewer.

Different Types of Refracting Telescopes

Let’s have a look at the types of refracting telescope used in the earlier times:

  1. Galilean Telescope: The Galilean telescope was designed by the great Italian scientist Galileo Galilei in 1609. It gives an upright image of the distant object. Despite the blurry and distorted images, Galileo used this telescope to explore the phases of Venus, the four largest moons of Jupiter, craters on the moon, etc. 

Galilean Telescope

Galilean Telescope

  1. Keplerian Telescope: The Keplerian telescope was invented by Johannes Kepler, a German astronomer in 1611. It gives a wider field of view and forms a greater magnified but an inverted image of the object. 

  2. Achromatic Refractors: The invention of the achromatic lenses led to a milestone in the evolution of refracting telescopes. Achromatic refractors were invented by John Dollond around 1758. 

Telescope Parts Names and Function of Telescope

1. Optical Tube

Optical Tube

Optical Tube

The optical tube holds the mirrors and lenses of a telescope. The main function of these mirrors or lenses is to gather as much light from distant objects during nighttime and form a clear image for the viewer.

2. Eyepiece



An eyepiece forms the magnified image of the object and passes it to the observer’s eye.

3. Focuser

A focuser is a tube consisting of an eyepiece, which can be moved using knobs to adjust the focus of an image.

4. Finderscope

Finderscope is used in the telescope tube in order to find out the direction of the object we want to observe. Only after adjusting the direction using a finderscope, do we need to observe through a telescope.

5. Star Diagonal

A star diagonal helps to view through a telescope comfortably by adjusting the light coming from a telescope.

6. Mount

A mount is used to hold a telescope and helps to rotate it in the direction of the observed object.

7. Tripod



A tripod is where the mount and a telescope sit. It has height adjustable legs, and it also prevents the telescope from vibrating during the observation. It should be strong enough to hold the telescope along with its mount.


We have explored the world of telescopes. Now we can summarize the major milestones during the invention of a telescope and its main parts.

Refracting Telescopes:

  1. Galilean telescope

  2. Keplerian telescope

  3. Achromatic telescope

Major Parts of a Telescope:

  1. Optical tube

  2. Eyepiece

  3. Focuser

  4. Finderscope 

  5. Star diagonal

  6. Mount

  7. Tripod

FAQs on Telescopes

1. Where are the use of telescopes?

Optical telescopes are used for astronomy and in many non-astronomical instruments, including: theodolites (including transits), spotting scopes, monoculars, binoculars, camera lenses, and spyglasses.

2. What telescope does NASA use?

The Hubble Space Telescope is a gigantic space telescope. Hubble was launched by NASA in 1990. Hubble is the length of a large school bus.

3. What is telescope made of?

A telescope consists of an optical system (the lenses and/or mirrors) and hardware components to hold the optical system in place and allow it to move and remain focused. Lenses must be made from optical glass, a special kind of glass which is much purer and more uniform than ordinary glass.