Telescopes are amazing because they allow us an unparalleled view of objects in deep space that we would not otherwise be able to see with the naked eye. Knowing how a telescope works will enhance your observing experience.

These instruments employ some highly specialized technology. They are accessible to regular people, albeit with a hefty price tag.

How A Telescope Works

However, those with loads of experience and those without experience can find themselves wondering how a telescope works.

How can looking into a telescope show you objects so far away and with such immense clarity?

Desperate to find out how a telescope works, and found yourself scouring the internet in search of answers?

Then look no further. While other websites might be full of complicated explanations of the inner workings of a telescope, we are here to explain it all in words that make sense and won’t have you scratching your head in confusion!

How Does A Telescope Work?

Put it simply, telescopes work by gathering light that emanates from distant objects and then magnifying that light. Doing so provides a clear image of things that would otherwise be invisible. 

For example, let’s say you were waiting for a friend to meet you. You might spot them in the distance, but they will likely appear a little fuzzy.

This is because not enough light reaches your eyes to form a clear image. A telescope gathers the light bouncing off that person and concentrates it towards your eyes. This results in a much clearer image! As a bonus, the eyepiece magnifies the image.

The ability of a telescope to gather light depends on the ‘aperture’ of the telescope.

What Is The Aperture On A Telescope?

The aperture of a telescope is the part of the device responsible for collecting light. It can be viewed as a bit like a bucket to collect rain. The only difference is that it collects photons rather than drops of rain.

Being a bit more precise the aperture is the opening that allows light to enter the telescope. This can be the objective lens on a refractor telescope or the open end of a reflector telescope (although it also depends on the size of the primary mirror).

The size of the aperture is the most important specification of a telescope. The larger the aperture, the brighter the image will be, and it allows for the observation of more distant objects. The aperture dictates the maximum possible magnification that can be produced and the telescope’s resolution.

Returning to the analogy of the bucket the aperture is akin to the opening in the bucket. If the bucket has a wider opening, it will collect more raindrops. In a telescope the wider the aperture, the more photons it will collect. In a way, a telescope can be viewed as a light bucket.

There is something that you should keep in mind. As the aperture increases, the amount of viewable sky is reduced if all other factors remain the same.

What Is The Largest Aperture On A Telescope?

The largest aperture telescopes are reflectors.

Currently, the largest aperture visible light telescope is housed on the Canary Islands in Spain. It is called GranTeCan, and its primary mirror is 10.6m (34.8 feet) wide.

GranTeCan allows astronomers to study very dim and distant objects.

The largest refractor telescope in the world is that found at the Yerkes Observatory at the University of Chicago. The telescope has an aperture of 40″ (102cm).

This telescope allows astronomers to observe very small details, but the lens is incredibly large. Its size makes it incredibly costly and occasionally difficult to keep in one position for long periods! 

What Are The Other Parts Of A Telescope?

The aperture is not the only part of the telescope that plays an important role. 

The Eyepiece

The eyepiece is an often overlooked part of a telescope. The eyepiece is responsible for magnifying the image that is gathered by the aperture, making the image clearer to the human eye.

The Tube

The most recognizable part of the telescope is the optical tube. This part of the telescope does much of the heavy lifting.

The tube is the part that holds the lenses and mirrors. It is responsible for keeping the optical elements aligned and for mounting the focuser.

The length of the tube varies on the telescope design and its aperture. It is a function of the focal length of the telescope.

Structural Support

To see anything clearly through a telescope, you must be sure it will stick firmly in place as you look through. The telescope must remain stable on the mount under it.

Towards this goal, you will want to use structural support that offers stability yet allows you to smoothly orient the telescope at various angles before locking it in place. 

What Are The Different Types Of Telescopes?

Now while all telescopes focus on gathering light and then magnifying it to create a clear image, some do it differently! 

Refracting Telescopes

Refracting telescopes work thanks to the curved lens, which gathers the light and then sends it directly down the tube to the eyepiece, which is responsible for magnification. The light is bent due to the properties of the lens material and the physical properties of light.

This was the first type of telescope to be invented! 

How A Telescope Works (1)

Reflecting Telescopes

As their name would suggest, these types of telescopes use mirrors to gather light from distant objects before magnifying the light via the eyepiece.

These telescopes are popular because mirrors are much easier to mould into the perfect shape for the job. The primary mirror can weigh much less than an equivalent refractor lens at larger apertures. Because of this and that they cost less to produce they are very popular today.

Unfortunately, aligning the mirrors requires careful work to create a clear and visible image. 

Catadioptric Telescopes

These telescopes are a perfect blend of the other two types. They use both lenses and mirrors to create much clearer images.

These are the most popular types of telescopes because they can condense the mirrors and lenses into a much shorter tube, which makes telescopes more accessible to everyday people.

Older types of telescopes needed longer tubes because the light would travel from the lens of the mirrors down to the eyepiece.

The distance traveled helped to make the image clearer. Catadioptric telescopes ‘fold’ the light, which condenses it down, so there’s no need for a long tube! It does this by reflecting the light a couple of times within the tube.

However, like anything, there is no free lunch. Many of these telescopes are considered ‘slow’. This is in relation to their long focal lengths resulting in a slow focal ratio. The focal ratio is the ratio of the focal length to aperture. A slower focal length will result in a dimmer image.

To Wrap Up

There you have it!

Simply put, a telescope gathers light using its aperture and then sends it down the tube, where the eyepiece receives it. The eyepiece makes the image clearer via magnification.

If you do not yet have a telescope and wondering how much one costs, you may like our article called How Much Does A Good Telescope Cost?

Frequently Asked Questions

How Do Telescopes Look Back In Time?

Technically speaking, telescopes gather light from objects that emitted the light considerably before it is observed in the telescope.

This is because light takes time to travel from place to place!

As an example, Polaris is 323 light-years away from us. As a result, we are seeing the star as it was 323 years ago.

How Far Back In Time Have We Seen?

We have managed to look at light that is 13.8 billion years old! This is from the energy that was left over after the Big Bang! Although strictly speaking it is not ‘light’ anymore.

James Web Space Telescope recently discovered a galaxy that formed 350 million years after the Big Bang (NASA).

Jason Anderson
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