How Do Telescopes See So Far?

Telescopes are tools whose main purpose is to magnify distant objects. The original telescopes and precursors to telescopes were used by humans to see vast distances over the flatness of the oceans. These spotting scopes were used by captains and navigators to see far off ships, approaching weather or land while at sea. Then, the idea of magnifying distant objects was taken and applied by scientists to looking up at the stars in the sky above us.

This opened up a whole new field of scientific study which is still fascinating to us today. But how do these telescopes see so far?

Telescopes operate on the basic principle of gathering light and focusing light. The more light you can gather, the farther you can see. If you can properly focus this light, you can image the light into an accurate representation of the distant object.

Light gathering without focus won’t produce anything useful. Focusing without adequate light gathering will leave you with great images of objects which aren’t that far away.

This process only works when everything is calibrated to work together properly in a way that becomes useful to the human eye. At the core are the laws and behaviors of physics that power all magnification devices from binoculars to massive space based telescopes.

The Basic Principles

A very simple process involving some extremely complicated engineering is taking place any time a telescope is pointed towards the sky. Once you have aligned the aperture, or light gathering opening, of your telescope skyward something begins to happen.

First of all, every photon in the universe that has an unobstructed path to the Earth is making its way towards us right now. At all times, photons are streaming our way but not all of them make it. This means distant stars are super dim and unseeable to the naked eye.

Your telescopes aperture is designed to gather light. This means that those faint and scattered photons from far off objects are being collected by your telescope. Imagine standing outside in the rain and trying to catch water droplets with your hands. Now, bring out a large funnel instead. That is the difference between your eyes and the telescope.

The bigger the aperture, the more light it can gather, and the farther away a telescope can see. That is why scientific and government telescopes are so massive, so they can see farther and farther away.

Once the light enters your telescope, it travels down the optical tube before hitting specially designed mirrors or lenses. Some telescopes, such as refractors, use lenses which are curved glass, to focus the light. Other telescopes such as reflectors, use thin mirrors to focus the light.

The light hits these curved, reflective surfaces and gets focused and directed towards your eyepiece. Then the image is taken in by the eyepiece and presented to your waiting eye.

The larger the aperture and the better refined the reflective focusing surfaces, the farther away you can see.

Highly Precise Optics

In order to gather light and produce images of super far off objects, telescopes employ extremely precise and highly engineered optics in order to produce the desired images. These objects are so far away, that any imperfection, flaw, or misalignment will render the view unusable or unseeable. That means that telescopes have to be extremely precisely designed and built in order to make the most efficient optics possible.

Without this engineering, everything would appear as blurry undefined light. Basically, nothing would appear in the eyepiece that would be considered recognizable.

This level of engineering and scientific design is impressive and highly precise which is one of the reasons that some telescopes can get really expensive at first glance. Once you realize what goes into making a telescope, the price will seem fairer.

When you get a telescope, you are not simply getting a nifty thing that you can use every once in a while for fun, you are getting a super well designed scientific tool that has been used for hundreds of years to unlock the secrets of the universe.

Magnification Perfected

We have gotten so good at this process of gathering light and focusing it that the best telescopes in the world can see for unimaginable distances. The Hubble Space Telescope, orbiting around the Earth, is able to see tens and hundreds of millions of lightyears away.

A lightyear is the distance that light can travel in a year. It measures roughly six trillion miles. But the fact that light can only travel this set distance over a set amount of time means that the farther away you look from the Earth, the farther back in time you are peering.

The sun is about eight light-minutes from Earth meaning, you are seeing the sun as it was eight minutes ago rather than in real time.

If you point your telescope at Alpha Centauri, one of our nearest neighbors, you are not seeing it as it is now but how it was about four years ago.

Peer at something ten million lightyears away and we are seeing it as it was ten million years ago.

When you think about this, it becomes mind blowing how awesome these capabilities are. Even with the naked eye, the light from those tiny dots of light started their journey to your retina a century ago, a millennia ago, an eon ago. It is truly amazing.

Universal Principles

Whether you are using a small, relatively cheap, telescope in your backyard or viewing images from the Hubble Space Telescope the principles being used to gather these images are the same. Light is gathered, light is focused, light is imaged. This is a science that is static across all telescopes.

NASA might have larger apertures, better mirrors, different reflective surfaces, and different imaging software but the basic principles and the results are the same: devices that can see far farther than the human eye ever could.