Peeking Into The Unknown — How Does A Telescope Work?

how does a telescope work

If there’s one thing that humanity has still barely explored, it is the vast space around our mother planet. It’s filled with countless stars and galaxies without an end. With the recently released pictures from the Hubble space telescope. You might ask the question: How does a telescope work?

With the advancement of technology, it’s no surprise that scientists have created telescopes so strong that they can even retrieve actual images of the stars by looking into space. Obviously, there are different types of telescopes, each with its advantages. Let’s dig a bit deeper into the world of telescopy to learn how they function.

What is The Function of a Telescope?

The literal meaning of the word telescope is to see far away, which sums up what these devices can do.

The primary function of a telescope is to collect light. You might think that our eyes perform the same function; they collect light and create an image. How is a telescope any different?

That’s because these instruments have far exceeded the capabilities of our weak eyes. When you look up at the night sky, I doubt you’ll be able to see a new galaxy formation or a red giant star on the brink of death.

Eyes — A Basic Light-Collecting Organ

Our eyes have extremely small apertures called pupils. This physiologically varies between 5-7mm depending on how dark it is. When the amount of light entering your eyes reduces in the dark, the pupil automatically dilates to let more light in. Hence, it all comes down to the size of the aperture of the light-collecting device. Wider apertures are able to collect more light and vice versa.

Distant stars and galaxies emit a lot of light, but their intensity is drastically reduced by the time it reaches Earth. On top of that, our eyes cannot pick up these weak light rays when bombarded by much more obvious light-emitting objects around us.

Telescopes — Light-Collecting Behemoths

The core differentiating factor that makes the light-collecting ability of telescopes far superior to eyes is their huge apertures. These massive apertures let in tons of light, allowing us to capture accurate images of distant objects.

This is coupled with the fact that telescopes are usually isolated in areas with little visible light pollution. It allows them to capture stunning images of objects in space. Some of these telescopes, like the James Webb Space Telescope, are floating in space, further adding to their isolation.


A power that almost all of us wish we had in our eyes is to magnify what we see. While this can’t be possible, there are means of doing this by using telescopes.

Distant galaxies are, well, distant, and it would be impossible to see them without some sort of magnification applied. That’s why every telescope has a magnifying eyepiece that can enlarge the image and allow us to see deeper into space.

However, it is essential to note that in order to magnify the scope’s image, capturing a large amount of light is necessary. Hence, everything other than a telescope’s light-collecting function is secondary. This is dependent on the amount of light that enters it.

How Does a Telescope Work?

woman looking through telescope

Now that we know the basic function of a telescope, we can more easily understand the intricate workings of the inside of these instruments. Essentially, every telescope fundamentally works by first collecting a lot of light, which it then uses to focus on a sharp image. The eyepiece then magnifies this image to produce a bright image of the objects in the space.

There are two main types of telescopes, each of which has a vastly different operating mechanism. Let’s dig a bit deeper.

Refracting Telescopes

These telescopes make use of the same kind of combination of lenses used in eyeglasses. They are also called optical telescopes.

A biconcave lens has an outward bulge on either side, which allows the light to bend, a property called refraction. This refraction allows the entering light to create an image that seems much closer than it actually is.

A refracting telescope is made out of a long, narrow tube that’s hollow from within. On either end of the tube lies a biconcave lens that refracts light. The larger of the two lenses is called the objective lens. It functions to grab and refract all of the incoming light from the telescopic aperture to form an image. The objective lens is so huge that sometimes it gets difficult to hold them.

On the other end of the tube lies the eyepiece lens, which takes this image and magnifies it before delivering it to your eyes. This lens is smaller in size compared to the objective lens.

Drawbacks Of Refracting Telescopes

This design is fairly old and poses a few severe disadvantages. The main issue with these telescopes is that glass lenses are extremely heavy, hindering their portability.

Another issue with lenses is that they have to be manufactured with extreme precision. If either surface of the lens has any imperfections, the resulting image will be distorted and unsuitable. Plus, these lenses take much more time and effort to clean and polish due to having two surfaces.

The majority of the public cannot use these telescopes in their backyards due to the fact that they are so heavy and expensive. That’s where the other kind of telescopes come into play and solve all of these problems.

Reflecting Telescopes

These kinds of telescopes make use of mirrors instead of lenses, which is much more convenient. These are also called the Newtonian telescopes after the name of their inventor, Isaac Newton.

A Newtonian telescope uses a set of mirrors that collect and reflect the light back to your eyes. There are two main mirrors in this telescope. The larger, concave mirror at the back of the telescope is the primary one. It collects all the light entering the aperture and focuses on the secondary mirror.

The secondary mirror is flat and much smaller. It is tilted at an angle of 45 degrees, allowing the light to escape through the eyepiece placed at the side of the body of the telescope. Because the objective mirror is placed at the far end of the device, it isn’t possible to place the eyepiece on the opposite end like in refractors.

The main advantage these telescopes possess over refractors is their light weightedness. Glass mirrors don’t have to be as large or thick as lenses, which allows the telescope to be much smaller in size and easy to carry. If the price of these telescopes fits your budget, you can buy one for yourself as well.

Another plus point is the maintenance of these mirrors. They don’t have to be cleaned on both sides like lenses do, and manufacturing perfect mirrors is far easier and cheaper than lenses. Hence it’s perfectly feasible to place them in your backyard under the night sky and learn to stargaze.

Drawbacks Of Reflecting Telescopes

While you may think that all the telescopic problems were solved with the advent of reflecting telescopes, that’s not the case. These new devices possess their own issues that need to be discussed.

The main problem with these devices is collimation. Collimation is the act of re-aligning the two mirrors present in your Newtonian telescope. With time, the primary mirror tends to displace from its original position. This is because most of the reflecting telescopes’ aperture is exposed to let in more light.

Another issue with these devices is coma. This is due to the comet-tailed images of every star or galaxy reflected off the curved surface of the primary mirror.


Telescopes have been gaining traction as more and more of the wide unknown space is uncovered. This caused many people to question themselves: how does a telescope work?

In this article, we discussed the basic working mechanism of refractors and reflectors and their drawbacks.

Now you can truly appreciate your favorite images of deep space.


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