How Do Telescopes Work
The telescope is our most important tool in Astronomy and is used to observe faraway celestial objects and electromagnetic radiation.
Telescopes are being used differently as time goes on. We used to only use them to see objects in normal light. Now we can leverage our technology gains to see different wavelengths of light in the universe.
This has opened up our studies with a lot more data than we previously had. This article talks about the different fields and categories of astronomy and what they mean.
Essentials of Telescopes
There are many kinds of telescopes. With many uses as well, there is a diverse market for every kind of telescope you could imagine. Narrowing down what your goal is can save you a lot of money in the end. When looking for a telescope, there are a few terms you should know.
- Aperture — This is the size of the mirror and is the most important factor.
- Focal Length — This is the distance from the mirror to the focal point.
- Magnification — This depends on the focal length and is a good indicator of the telescope.
- Focal Ratio — The focal ratio is the relationship between its focal length and the aperture of the telescope.
To do any meaningful research, you need a telescope, a wavelength filter or spectrometer, and a detector. The telescope needs to be as large as possible. A larger aperture gathers more light.
Bigger telescopes see fainter objects. Once they gather light, they can focus this light into an image. This is how they generally work, no matter the type of radiation.
The wavelength filter can be a variety of devices. Filters can be simple or complex. They can show you one color or a rainbow. It depends on what you are after. Different colors give different information.
After light has been collected, you must use a device to detect the wavelengths you are after. With a detector, you can get long exposures. This is key to observing faint objects far away.
Optical telescopes collect visible light. That is why they are optical. Seems simple enough, right? It really is. The more light we then collect, the more we can see.
When people think of telescopes, these are the type that are thought of when first learning the basics of telescopes. It is how we use telescopes. There are two main kinds of optical telescopes:
- Refracting — bends light that is then focused.
- Reflecting — uses a mirror to reflect light.
Refracting scopes use a lens to gather and concentrate light. They do not do colors as accurately as they should either. A lens will also absorb some frequencies through the atmosphere. This makes a refracting telescope a poor choice for infrared studies.
Using a lens in your telescope is also more expensive. This is because a lot more quality and effort goes into a lens.
Reflecting telescopes use mirrors instead of a lens to work with the light that is captured. Since they use a mirror, there are no absorption issues to deal with. You can also use a much larger mirror than a lens.
So scopes that are large almost always use a mirror. Among reflecting telescopes there are different ones as well:
- Newtonian-reflected to an eyepiece at side of instrument
- Cassegrain-light reflects light at the end of the instrument
The Keck Telescope and the Hubble Space Telescope are the two most famous. They based Keck in Hawaii while Hubble is orbiting in space.
Size Of Telescopes
The size of telescopes has grown over time. Originally they were pretty small in Galileo’s day. However, thanks to modern science, we are getting larger ones all the time. Indeed, the space telescopes are also getting bigger.
What is the advantage to a larger telescope you may ask? Well, the larger the telescope the more light it can collect. It is all about the amount of light it can gather. This helps us see far off objects.
The telescope’s mirror directly affects how much we can see. This helps with another issue, which is the telescope’s resolving power. Its resolution is also very important because it lets us see the details of objects in space.
For example, it lets us study far off objects and refine our theory of star classification.
A larger mirror also helps with diffraction. This is the tendency of light to bend. Basically, the larger the mirror the less bending of light, or diffraction, that you will have.
Presently, telescopes can be huge. The largest ones are 10–11 meters in diameter. Larger ones are being built. I imagine, there will always be a larger one being built.
Imaging With Telescopes
Imaging and the field of astrophotography are very popular these days because looking through a telescope is looking back in time. When individuals first want to know how telescopes are used, imaging the night sky is one of the first choices.
More and more people all the time are doing this because of how useful and fun it is. The pictures created are just breathtaking. Computers and associated software are being used to make this process even easier and more reliable.
Done correctly, they can even reduce background noise in pictures. The background noise also has its own characteristics. It can then be analyzed and useful information will be the result.
So what exactly is imaging then you may ask? It is the process of taking very long-exposure photographs of cosmic objects. While your camera is doing this it goes onto its film.
There is a slight problem with this though. Can you guess? Yep, the Earth and everything moves. For astrophotographers, to take those stunning pictures the telescope has to move.
If you are interested in astrophotography, then you will buy a telescope that has a guidance system included in it that will track planets and stars.
This means there is a small computer that will adjust position in far greater detail than we could ever do by hand. The purpose is to keep our object that is being photographed squared.
Most often this was done by hand, and it could be quite difficult. It was easy to make errors doing it this way.
Fairly recently technology has advanced and new CCD chips have come on to the market. CCD stands for charged coupled devices. These chips take digital images of objects. On the CCD, a pixel stores the photonic information that it gathers.
Just like the previous method it takes time to gather enough light and information on to these chips but the results can be wonderful. These CCD’s record starlight and allow much greater visibility into the heavens.
This process allows us to detect and analyze the faintest objects. Without doing this, we would not know they were there.
These chips also can auto guide, making the following of an object a much simpler process if you have the cash to pay for the hardware.
These chips are much more efficient than previous methods. Think cell phone camera versus Polaroid.
This leads to the next subject, which can be very useful. It is the study of brightness of any object. We call this photometry. Astronomers combine photometry with the use of filters to analyze certain wavelengths.
As each range of wavelength can have unique characteristics, this is precious. To measure the light, a telescope takes it in and then we use an instrument called a photometer. It measures the amount of light received.
Spectroscopy, which is the study of the spectrum of light, goes right along with this. Without even looking at the source image, we can infer much from this and is one of the most important topics when dealing with the basics of telescopes.
It is hard to get splendid pictures while on Earth. It is not really our fault though. The atmosphere affects our view so much. Not a lot we can do from here. Therefore, we launched telescopes into space.
Turbulence in the air is constantly messing with our telescopes and imaging. An interesting fact is that turbulence has less effect on longer wavelengths.
I do not know why this is but guessing it is because smaller wavelengths are much more sensitive. Because of turbulence, we usually place telescopes at high altitudes.
Resolution is the detail in an image. We want as much as possible. With higher resolution, the smallest features become apparent. This is vital in the study of astronomy. Aperture size is the key ingredient of resolution.
The larger the aperture, the sharper the image becomes.
Our atmosphere contains many gas pockets. These pockets catch and distort the starlight. They distort it by making it reach Earth in weird ways. This is the big problem with optical telescopes.
The distortion of our atmosphere disrupts viewing a lot. Therefore, astronomers go to the highest and driest places available for viewing.
Radio astronomy, as we know it, was first started in the 1930s. We credit it to Karl Jansky. He was working on radio communications when he discovered radio waves from an unknown source away from Earth.
Since an abundance of radio waves reach us on the ground, radio astronomy is a growing field. Also, since radio waves are a lot longer than, say gamma waves, the atmosphere does little to them.
In fact, radio waves are the longest form of radiation. Radio astronomy has only begun in the last few decades so we have a lot to learn about these techniques.
We can use radio waves to map out areas in space with much greater detail than using optical astronomy. It’s like this because the atmosphere doesn’t affect a radio telescope. This is very useful because we can not actually see these areas with our eyes.
Radio telescopes have an enormous dish which is their collecting area for the radio waves it captures. It is so large because radio waves are quite rare compared to other kinds of radiation that hits the Earth.
Therefore, we need to maximize our chance at capturing these them. They also operate differently than optical telescopes in that they only see a few wavelengths at a time of radiation.
A tremendous advantage with radio astronomy is that poor conditions mean nothing. For example, if you want to go see a meteor shower and it is cloudy, then you are out of luck. It is the same situation with any optical telescope on Earth.
If there is too much moisture or cloud cover, then we just have to wait until conditions get better. Radio telescopes do not have this problem as radio waves are not affected.
One of the main issues with radio astronomy is the poor resolution. Those telescopes are not near as good as optical telescopes in showing details of an object. This is where interferometry comes in to play. Interferometry is when two telescopes are used together to view an object.
They are linked together to form an array of telescopes. This makes it possible for them to be very geographically separated.
As each radio telescope takes in data, we then combined the data again using special software that makes a superior image than either took to begin with.
When used together like this an interferometer can make brilliant images which get very close to optical images. An important fact to know is that great distances separate the two radio telescopes that work together.
By this I mean they can be on different continents or even further than that sometimes.
A very interesting thing happened as technology and computers got better in recent years. Instead of just detecting radio waves, we can now also detect smaller wavelengths. This opens up our universe even more.
Infrared telescopes are used to study longer wavelength radiation, and it is a good example of how telescopes are used to study light that we can not see. This is a very popular field.
Longer wavelengths are easier to detect than much shorter wavelengths like gamma rays. A good example of this type of astronomy is the Spitzer Space Telescope. It has given us some truly great images.
This is an important field because it lets us see the universe without the issues of light pollution. Interstellar dust is everywhere out there.
There is so much of it, it makes some gigantic clouds. All of this dust makes seeing difficult. The dust can completely block out a lot of faint objects.
Therefore, studies of the infrared spectrum are valuable. They let us see without our eyes. In the electromagnetic spectrum, infrared lies between visible light and microwave radiation. Its wavelengths are a little shorter than microwaves.
Any object that produces heat gives infrared radiation off. It can be a lot of heat like the sun or just a small amount like the snow. Both still puts off some heat and therefore radiate infrared radiation.
In the shorter wavelengths, we have ultraviolet astronomy. This is short wavelength astronomy. In this niche area of astronomy, it is ultraviolet radiation that is studied. The wavelengths of this radiation are around 90 to 350 nanometers.
As with all the other areas of astronomy, you can tell a lot about the object when studying its radiation. Examples of what we can infer are densities, composition, and temperatures.
We divided the ultraviolet spectrum up into the near, far, and extreme ultraviolet regions.
One of the cool things about ultraviolet radiation is that the objects with the highest temperatures in the universe give off a lot of ultraviolet radiation. This makes it an excellent source to study.
To study this type of radiation, we usually have to analyze data taken by space telescopes. I should point out that we use space telescopes to gather ultraviolet radiation because the Earth’s atmosphere blocks most of the ultraviolet waves.
Basically, to get to them we must be in space.
High Energy Astronomy
This is the part of the spectrum that is least known to us. High energy astronomy deals with gamma rays and x-rays. They are hard to detect and to capture. Gamma rays, in particular, have the most energy of any other type of radiation.
One of the really cool things about them is that they penetrate everything. This makes gamma rays hard to deal with.
An interesting fact is that the gamma rays and x-rays cover a large part of the electromagnetic spectrum. In contrast, visible light only covers a small fraction of the spectrum.
Just about every day we are discovering more sources for x-rays and gamma rays. The list is skyrocketing. However, there are many more sources for x-rays than gamma rays. In our galaxy, the Sun is the closest emitting source.
Throughout the galaxy there are sources that send forth much more radiation than our Sun. We call these the x-ray binaries which are systems of stars in which one is probably a neutron star.
These objects produce fantastic amounts of high energy radiation. Another super source of x-rays is supernovae which can send the detectors through the roof.
Right now there are only about 3000 known sources for gamma rays. That number should explain how rare they really are. As a result, it is more difficult to do a study using spectroscopy because other wavelengths are much more common.
We can sometimes wait a long time before we can detect one. Even more rarely we can observe gamma rays in lightning bolts or certain kinds of nuclear explosions. The typical gamma ray is highly energetic. This means that it contains an abundance of energy.
Its energy is so great that we use it in the medical industry to kill certain cancers. I can’t think of a better way to harness nature for a good cause!
The Astronomer’s Life
Astronomers rarely peer into an eyepiece like they used to. There are a couple reasons for this. One reason is that technology has advanced, and it allows us to do so much more with the data gathered by a telescope.
The other reason is that the atmosphere is degrading which makes seeing objects a lot harder. This is mostly due to all the satellites launched in the last few years. A lot less star light gets to us now.
The light that we can see is often distorted because of our atmosphere.
Most Astronomers spend their time in front of a computer. They are using software to analyze data. They want to use the good telescopes but these have limited time. So they might get a few days a year and spend the rest of the time analyzing their data.
I hope this has given you some inspiration for studying Astronomy. It is a wonderful science and there is much yet to learn. You even have several fields in which to specialize in. Your first step is to get a telescope and start exploring and see where it takes you.
New telescopes are constantly being built. They are larger and more advanced. Hopefully, new discoveries will keep rolling in. I am really excited about the James Webb Space Telescope. It should launch relatively soon.
Thanks for Reading
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Originally published at https://sciencebyjason.com on July 9, 2021.