Telescopes: Astronomers' primary tools.

 

Translated from Haitian: https://haitiastronomie.blogspot.com/2023/03/teleskop-zouti-principal-astronom-yo.html

Every trade or profession has its main tool. If you're a doctor, you use stethoscope, if you're a builder, walk around with your tool, if you're a soldier, your arms must always be there... so also if you're an astronomer, you'll need a telescope to study the stars. Let's take a look, with Captain Astro, at the telescope.

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First of all, let's understand that the word telescope actually includes 2 types of devices: one made of lenses, they call it astronomical lunette, and another made of mirrors, which really bears the name of the telescope.

Who invented this device? There is still some dispute about the true origin of the telescope, but most historians think that it was a Dutchman named Hans Lippershey who invented the telescope...let's say astronomical glasses; he filed the first patent for this device in 1608; but some historians think that Giambattista della Porta would have invented it in Italy in 1586; well, there are still other people who give other names... However, the person who will give this device the most fame is another Italian who was called Galileo Galilei in 1609, especially when he was going to show his astronomical glasses in senate in the same year 1609. Therefore, it was not Galileo who invented astronomical glasses, but he was the one who used them for the first time to observe stars and other things in the sky. He will make several discoveries with the astronomical glasses such as 4 moons orbiting the planet Jupiter, something that would have been impossible in the way astronomy was understood at that time.

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The principle of astronomical glasses (lunette) is simple: it is a tube with, at each end, a lens; one to receive the light from the star you are observing, another to put your eyes to see. The lens through which you observe is technically called the eyepiece lens, and the other that receives the starlight to form the image is called the objective lens.

The image that is created will be clearer if the device receives more light, it is logical. Therefore, the wider the objective lens, the larger the diameter, the more beautiful the image you will see through the eyepiece.

So optical scientists are working harder and harder to make ever larger lenses.

In 1668, a great scientific man named Isaac Newton came up with another concept that will bear the true name of the telescope. He used a mirror preferably as the main objective and the eyepiece was placed on the side of the tube for the astronomer to make better observations. It is a concept that has been very popular since then, until today, where you will find many amateur astronomers' telescopes designed in this way. There are several variants of telescopes derived from this model, such as Cassegrain, Schmidt-Cassegrain, Nasmyth and tilting. They each have their advantages and disadvantages. In any case, for all, the most important thing is the diameter of the opening, that is what will explain that, thanks to technology, optical specialists will develop devices with larger and larger opening diameters, as I said it already!.

There, they will understand that making large astronomical glasses, therefore with lenses, is more complicated than making large telescopes with mirrors. While the lens has 2 sides to manage, therefore, you can only fix it on the edge, a mirror has only one side to manage, and the other side, which is behind the mirror, is available to fix it, support it.

Here, we understand well! The lens uses both sides to, firstly, receive light, and secondly, transmit light to the eyepiece glass. Therefore, to keep the lens, only on its side, where the light does not have to pass, you can fix it in the tube of the astronomical lunette. But for telescopes made of mirrors, the area that reflects the light is on one side, not on both sides. So you have more freedom to use the back of the mirror for fixation and to have other devices in addition to the telescope, ... well.., if you need it. You understand,...

You are not limited to the edge of the mirror only, as it would be for a lens!

Astronomers and optical technicians will build large observatories using the mirror principle. So actually the largest telescope on Earth is in the Gran Telescopio Canarias observatory (GTC) built in 2005 in the Canary Islands in Spain; it has an opening that measures 10.4 m. However, there are projects underway to build even bigger observatories and telescopes, such as the Extremely Large Telescope, in the Atacama Desert in Chile, which in 2024 will become the largest eye in the sky.

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While we are talking about eyes, I will take the opportunity to let you know that astronomical lunette use the same basic principles as the human eye, say like the eye also has a lens, called crystalline, which receives the light that passes through an opening that is called pupil.

It is the crystalline that will make the light focus on the retina, exactly where to focus so that you can see correctly.

Before Galileo began using astronomical glasses, this did not prevent astronomers from making observations and even discoveries in the night sky. They served, obviously, with 2 eyes in their heads. And you must protect your eyes, there are a quantuty of lights you must not look at; therefore, never try to look at the Sun with astronomical glasses or a telescope directly. They say that this is what made Galileo blind before he died. Well, not everyone agrees with this thesis, for them it is because Galileo was getting old, he became sick and he was blind. However, please never try to look directly at the Sun with these devices. If there would be special protection designed for this and would be installed in the telescope, and your strength should be verified before you use it. So you could do solar astronomy... But watch your bones!

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Telescopes allow us to see many things in the night sky, but don't forget, we are on Earth, there is also an atmosphere, a layer of gas that covers us, which blurs the light of the stars before they reach the telescopes. This limited all the observational work that astronomers could do.

Even though the astronomers need the atmosphere to breathe, it bothers them a lot in that sense too, worries... in addition to the light pollution that they can find more near the big cities. Well, opticians and astronomers also came up with a series of techniques to see if they could limit the impact of the atmosphere on astronomical observations. First, they think it would be more beneficial if they put the observatories higher, at the top of the big mountains, so the density of the atmosphere will decrease, there will be less fluctuation, and the images will be clearer. In the mountains too, they are far from the big cities, that means... there is less light pollution, and radio interference. So it would be better that way.

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A series of technologies have also been developed to improve the performance of large telescopes in relation to the problems that the atmosphere provides in their observations; technology called active optics where the main mirror, made of several small mirrors, can make small changes in position thanks to high computer control. Apart from that, they can counteract the disturbances that the atmosphere could give by transmitting the light of the observatory glass. There is also another technique called adaptive optics where the observatory shoots a laser beam into the atmosphere, and creates a sort of artificial star that allows them to reframe and correct the disturbances in the images captured by the observatory.

Also, another solution to avoid the disturbance that the Earth's atmosphere can give by letting the light pass to reach the Earth, would be to exit and go completely in space. Well, the problem of interference with atmospheric gases is completely over... but it also costs money, ... a lot of money, to put a telescope in space, and repair it if needed. But the astronomers did it anyway: like the Hubble Space Telescope, which was built by NASA and ESA, which went into space since 1990. It gave many beautiful pictures during its reign, and the James Web Space Telescope, which came later. He took over and will continue to do good work in astronomical observation. Well, there are already plans for other space telescopes, and the big space agencies even plan to build astronomical observatories on the farside of the Moon, where the matter of disturbance to observe the sky does not even exist! ...Almost not, except for a few meteorites...remember there is no atmosphere on the Moon!

Here, take a breather to enter another affair in the matter of telescopes.

Telescope is like a machine that goes back in time, the image you see is something that was made in the past and that takes time to reach you on Earth, at the speed of light.

It's like a messenger who was on the way and ended up not reporting what happened when he was leaving, with the message; what's happening behind him, when he's finished taking off, he doesn't know... in fact, all the images you see in the sky, with or without a telescope, this is the past!

I remind you that light, therefore our main messenger in astronomy, is an electromagnetic wave with various frequencies or wavelengths. Not all frequencies pass through the Earth's atmosphere, such as gamma rays, X-rays and parts of the UV and infrared. Of what comes in, it is a small part that humans can see with their eyes, at wavelengths of 400-700 nm (380 nm to 780 nm), which is why they call it visible light. Well, all we were talking about recently was about the telescope that captures visible light. But the higher you go in the atmosphere, the more likely you are to capture some of the wavelengths that don't reach the ground at all, such as some UV and some IR; but X and gamma rays do not penetrate at all, neither reach Earth. The Sofia telescope, in a stratospheric plane, may allow you to observe more IR, and the Hubble telescope... or the James Webb Space Telescope, they can see far more infrared than that on Earth or in the atmosphere, in addition to being shielded from atmospheric gas disturbances. There are other telescopes in space that allow them to look at other wavelengths that do not even reach the Earth, such as the Chandra Telescope that makes observations in X-rays, and the GLAST Telescope (GLAST is an acronym for Gamma ray Large Area Space Telescope or large space radiation telescope gamma), renamed Fermi in honor of the famous Italian physicist.

In the matter of telescopes getting bigger and bigger, in order to see further back in time, scientists began to think a lot about how to increase the diameter of the place to receive light in the telescope. They arrive at a technique called interferometry where, in an array of telescopes, the distance between them represents the diameter. So, for example we can reach a diameter of several km; and there are even projects to use space to establish a network of telescopes for interferometry. There, we can understand that the diameter of the openings can reach many km. However, in terms of resolution, as the images would appear more clearly, this technique has its limits: it is more useful in radio astronomy, as it is observed in the radio range.

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Telescopes are a very important tool for astronomers, whether they are amateurs or professionals: both of these categories can make discoveries that help us better understand where we live, and one day we will get to know more always about who we are, where we came from and where we are going.

There are other tools in astronomy. Although the telescope is the main one, there is also spectroscopy, there are also devices to detect gravitational waves, neutrinos, or even cosmic rays, because light is not the only messenger in space. In the meantime, protect your eyes, ...even if they are not as powerful as the devices, they are yours.