Large Diameter Telescopes

Why do we use large diameter telescopes today?

A long time ago, when the ancient Greek philosophers discussed nature, they came up with the idea that the celestial realm is a completely different world and that the rules up there are completely different from those on Earth. But our world could only enjoy the view seen with the naked eye. The situation remained the same for more than a thousand years. Fortunately, astronomers like Galileo discovered that there was more to the sky than our eyes could observe. In order to take a good look at those faraway stars, they began building telescopes.

The first telescopes were quite simple, consisting of only a few lenses, and could only magnify an object to four times its size. Due to imaging problems, many people focused on solving those issues, and a community of telescope makers began to form. As time progressed, the design improved, so different models of telescopes were made. The newest ones are large diameter telescopes that solve the problems of vagueness and unclear images.

Photos taken by old telescopes that do not have good apertures are blurry, so further analyses are difficult or even impossible. This is quite normal since stellar objects (stars, nebulae) and galaxies are so far away. Because of the large distance, they seem both small and pale. Some are so vague that they can’t be observed without the use of an excellent large telescope. If you wish to take a good look at galaxies and stars, you’re going to have to use a large diameter telescope.

How do large diameter telescopes function?

Telescopes, like cameras, need a good aperture. The aperture is the opening on the camera that takes the photo. It has to be big, so it can gather more light. There are two important optical components: lenses and mirrors. These should be large since their size determines the amount of light gathered.

Two abilities are crucial for a telescope: the ability to gather as much light as possible and its resolving power. Good light collection means that you get a bright photo. More light means that blurred objects will become visible, and there is more light for you to analyse, which is done by means of spectral analysis. Since we are performing the spectral analysis on Earth, we can only work with the light that we gather here with our telescopes.

The resolving power determines the sharpness of the image. It represents the ability of an optical instrument to distinguish small details. Sharpness is important, so you do not miss out on any details. Imperfections take a huge toll on analyses, so the optics are constantly improved to ensure that blurriness does not occur. When observing a very small celestial body, good magnification is very important. It enables you to magnify the size of the image of the celestial body so you can take a good look at it without a loss of sharpness. If the resolving power is good, you will get to see a celestial body in great detail.

If that body is small, you also need good magnification. You should know that not all wavelengths can pass through lenses, so this affects the images and any subsequent analysis. Lenses also face issues with two types of aberration. This makes them less favoured in comparison to mirrors that are relatively simple to make. Because of this, most telescopes rely on mirrors.

What do you do after getting good images?

After getting good shots, you have to analyse the light gathered by the telescope. Spectroscopy is used here, so you get to know the spectra first. Spectra can be produced for any energy of light, from radio waves to gamma rays. If you have seen a rainbow, you have seen an example of a spectrum. Spectra are produced by the separation of the components of light by wavelength. Note that there are different types of spectroscopy, depending on the spectra you analyse. For example, there are infrared (IR) spectroscopy and ultraviolet-visible (UV/Vis) spectroscopy.

Spectroscopy is of great use to astronomers because they can only rely on observations. Astronomers and astrophysicists can determine the speed of a celestial object or its composing elements thanks to spectroscopy.

What prevents us from getting good images?

In order to get clear and sharp shots, you need the light of the analysed body to be uninterrupted and clean. Clean means without any other light sources interfering with the telescope. Unfortunately, on Earth, we face two key issues: atmospheric turbulence and light pollution. Due to light pollution, telescopes must be located in remote areas. Modern cities are well lit at night, so light pollution affects image taking. Actually, you probably cannot even see the starry sky if you live in a city.

Air (atmospheric) turbulence (also known as ‘seeing’) reduces the resolving power. Since the atmosphere is never still, different layers mix all the time and make the incoming light change its direction when passing through. This affects the amount of light reaching the aperture, so the images are distorted. This means that the resolving power is diminished because of this phenomenon.

Examples of large diameter telescopes

Let’s now take a look at some large diameter telescopes.

The Giant Magellan Telescope (GMT)

Giant Magellan Telescope. commons.Wikimedia.org

This is a telescope with excellent light-gathering ability that produces images with excellent resolution. Its main goal is to help scientists learn about exoplanets, galaxy formation, and other stellar observations. It belongs to the 30-metre class telescopes and is made up of seven segments. Each of them is 8.4 metres in diameter.

If you look at the picture, you will see that these segments form one huge mirror. It is the biggest infrared telescope, and its light collection area is 382 m². The fact that it is an infrared telescope means that it sees the infrared part of the spectrum, which we cannot see with our eyes. This telescope minimises the light’s path when light reflects from one mirror to another. In comparison to the Hubble Space Telescope, this one has better resolving power.

This picture shows the same part of the sky taken by GMT and the Hubble Space Telescope. As you can see, GMT enables you to get better and sharper images.

The Thirty Meter Telescope (TMT)

The Thirty Meter Telescope

TMT is located in Hawaii on Mauna Kea, the sacred place of the native people. It is an isolated location, so there is no light pollution. Also, the weather conditions are very favourable, and so the photos taken by TMT are very sharp. Combined with its good design, TMT generally produces excellent photos. It was created so it could gather the light belonging to the part of the spectrum between near-ultraviolet to mid-infrared.