How do Telescopes work? And what makes them so powerful?

Telescopes are among the most amazing tools in the world. They help us see faraway objects in the night sky that we may never reach. It is like piercing through the veil of dreams, so near, yet so far, what we see is mesmerizing thanks to these wonderful inventions.

But how do telescopes actually work? We know that the first telescope was patented in 1608, and since the last 400 years these magical instruments have greatly increased in complexity. As such, today we are going to answer questions such as:


  • How do telescopes work?
  • What are the lenses?
  • Why mirrors work better?
  • Who invented the telescope?
  • What is the most powerful telescope?
Credit: NASA

How do telescopes work?

The earliest telescopes, and even many today, focused light using pieces of curved, clear glass, called lenses. Today, there is a second method to gather light, and that is by the use of curved mirrors [1].

The principle remains the same, the shape of the lens or mirror in a telescope concentrates light, and that is what we see when we look into a telescope.

These elements are called optics. The most powerful telescopes today can see very dim objects which are unfathomably far, however, what dictates their power is how big their optics are, be it lenses or mirrors.

Telescope parts
Credit: NASA

Size matters when it comes to telescopes, the bigger the optics, the more light the telescope can gather, this is called the aperture. Light is then concentrated by the shape of the optics.

The two general properties of a telescope are how well it can collect light, and how much it can magnify the image. The magnification depends on the combination of lenses used.

The eyepiece, which is the lens near the eye, acts as ordinary magnifying glass, thus enlarging the image. This feature by almost any telescope by using different eyepieces that fit and this is why aperture is a more important feature.

What are the lenses?

Lenses form images by refraction and are usually made out of glass or plastic. The mechanism is simple, the lens gathers light from distant objects and bends them so that they can converge to a single point called the focal point.

The distance from the lens to the focal point is called the focal length of the lens. Refracting telescopes use this type of lenses. Most refracting telescopes use two types of lenses.

Telescope parts
Credit: NASA

A large lense, which is called the objective lens, and the smaller lens used for viewing, is called the eyepiece lens. The size of an image produced by a lens is proportional to the focal length of the lens [2].

The longer the focal length, the larger the image. Image brightness partially depends on how much light is collected by the telescope, and the light collected depends directly on how large the objective lens is.

If the diameter of an objective lens is doubled, the light-gathering power also increases by a factor of 4. The magnifying power, on the other hand, is the ration of an object’s angular diameter to its naked eye diameter. This depends both on the focal length of both lenses.

Why mirrors work better?

Lenses have limitations since they create a type of image distortion known as chromatic aberration. As light passes through the lens, different colors bend through different angles and are brought to a focus at different points.

This creates a halo that surrounds whatever you see through the telescope. However, by adding a thin lens of a different kind of glass behind the objective lens, you can correct image aberration [3].

Telescope parts
Credit: NASA

Lenses have other problems though, they are difficult and expensive to make without any defects. Glass also absorbs more ultraviolet light, and visible light is dimmed as it passes through the lens.

The reflector type telescopes, on the other hand, use mirrors instead of lenses. Unlike a lens, a mirror can be very thin, and regardless of its size, the thickness doesn’t necessarily increase.

Light is concentrated by bouncing off of the mirror in reflector telescopes. The mirror must have the right curved shape, and since mirrors are one-sided, they are much easier to clean and polish than lenses.

However, mirrors also have their own problems. The curved mirror in a telescope flips the image upsidown, but this is easy to solve by using another image to flip it back.

Electromagnetic spectrum
Credit: NASA

Probably the best benefit of mirrors is their weight. They are much lighter than lenses, and this is why space telescopes such as the Hubble Space Telescope, and the Spitzer Space Telescope use them [4].

Who invented the telescope?

The telescope is probably one of the most awe-inspiring inventions of humanity. Though it may be a simple device, which makes far-away things appear near, the telescope gave observers a new perspective of how vast the universe is.

But who invented the telescope? In 1608, a Dutch eyeglass maker named Hans Lippershey applied for a patent, his invention, a telescope. He claimed that this device could magnify objects three times [5].

This fist telescope had a concave eyepiece aligned with a convex objective lens, and there are two tales of how Lippershey came up with the idea of such an invention.


The first one goes like this, Lippershey observed two children in his shop holding up two lenses that made a distant weather vane appear closer, and thus his inspiration for the telescope.

The second tale is a bit more shaddy. Some say that Lippershey stole the design of the telescope from another eyeglass maker, Zacharias Jansen. Both men lived in the same town and worked on optical instruments.

However, scholars disagree with this, since there is no real evidence that Lippershey didn’t develop the telescope on his own. He was the first to apply a patent for this creation, and thus he is the most credited for the invention of the telescope.

What is the most powerful telescope?

Times have changed greatly in the world of telescopes. From Galileo Galilei’s crude telescope, which helped him establish that not all things revolve around Earth, to today’s modern space telescopes, such as the Hubble Space Telescope, which observes distant galaxies and stars at unfathomable distances [6].

Hubble Space Telescope
Credit: NASA

But what is the most powerful telescope in the world? Can we continue improving the telescope? Undoundebtly, the most powerful telescopes in the world are the space telescopes.

These devices do not suffer the consequences of Earth’s atmosphere which limits their viewing capabilities. For a long time, the Hubble Space Telescope has reigned supreme in its own right, but things change.

Today, the James Webb Space Telescope is on its way to being launched into space. It will eclipse the Hubble Space Telescope on all fronts. It was designed since 1996, and scientists still work on it to this day [7].

Some predict that it will be released in March 2021. The JWST was designed by NASA, the European Space Agency, and the Canadian Space Agency.

James Webb Space Telescope mirror
Credit: NASA

This new flagship will have a broader range of investigations across the fields of astronomy and cosmology. It will observe the most distant and oldest objects in the Universe, bringing us closer to a deeper understanding of how everything began.

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