The father of modern astronomy, the Italian physicist Galileo Galilei, who in 1609 proved that the Earth revolves around the sun, did something that forever changed the history of science and how we see the universe: he invented the telescope. Since then, different types of telescopes have been created as technology has advanced. We find telescopes that can only be used by scientists and telescopes for the general public.
For this reason, we are going to dedicate this article to tell you about the different types of telescopes that exist, their characteristics and what function each one of them has.
What are telescopes
A telescope is an optical instrument that allows you to observe distant objects and celestial bodies in greater detail than is visible to the naked eye. In other words, it is a tool capable of capturing electromagnetic radiation such as light.
The ability of telescopes to process electromagnetic waves, including those in the visible spectrum, leads us to emphasize that while the general idea that telescopes increase the size of objects through a series of lenses is ingrained, it is not true.
In other words, instead of magnifying the image with a magnifying glass, the telescope collects the light (or other form of electromagnetic radiation) reflected from the objects in the universe that we want to observe and, after processing this light information, reconstructs it into a image. They do not enlarge the image.
types of telescopes
There are about 80 different types of telescopes, but the differences between many of them are very subtle and only relevant from a very technical point of view. Therefore, we have compiled all these types and divided them into basic families based on the type of electromagnetic radiation they can handle and their basic design.
optical telescope
When we think of telescopes, we generally think of optical telescopes. They are capable of processing the portion of electromagnetic radiation that corresponds to the visible spectrum, which has wavelengths between 780 nm (red) and 380 nm (violet).
In other words, they are telescopes that capture the light from the objects we want to observe. These instruments are capable of increasing the apparent size and brightness of objects. Depending on how they capture and process light, optical telescopes can be divided into three main types: refractors, reflectors, and catadioptric telescopes. If you are interested in learning more about how these instruments work, consult our guide on how a telescope works.
refracting telescopes
A refracting telescope is an optical telescope that uses lenses to form images. Also known as diopters, they are the ones used before the introduction of more advanced technology in the early XNUMXth century, and are still used by amateur astronomers.
This is the most well-known type of telescope. It consists of a set of lenses that capture light and concentrate it at what is called the focal point, where the eyepiece is located. Light rays are refracted (change direction and speed) as they pass through this system of converging lenses, causing parallel rays from distant objects to converge at a point on the focal plane. It allows you to see large, bright, and distant objects, but it is very limited technically. If you want more information about telescopes, you can consult our guide on telescope types and their uses . Also, if you would like to learn more about the advantages of a reflecting telescope, visit our guide on reflecting telescopes.
Reflecting telescope
A reflecting telescope is an optical telescope that uses mirrors instead of lenses to form an image. It was originally designed by Isaac Newton in the 17th century. Also called reflectors, they are especially common in amateur astronomy, although professional observatories use a variant called the Cassegrain, which is based on the same principle but has a more complex design.
However, it's important that they are made of two mirrors. One is at the end of the tube and reflects the light, sending it to a mirror called the secondary mirror, which in turn redirects the light to the eyepiece. They solve some problems with refractors, since not using lenses eliminates some chromatic aberrations (less brightness distortion) and allows you to see more distant objects, although they are of lower optical quality than refractors. As such, they are useful for observing fainter, more distant objects, such as galaxies or deep nebulae. If you want to learn more about how to identify celestial objects, we recommend reading about the characteristics of Neptune . You can also read about [the other topic] for more information.
catadioptric telescope
A catadioptric telescope is an optical telescope that uses lenses and mirrors to form an image. There are many types of catadioptric telescopes, but the most famous is the one mentioned earlier: the Cassegrain telescope. They are designed to overcome the problems posed by refractors and reflectors.
They have good optical quality (not as high as refractors), but they won't allow you to see distant and faint objects like reflectors do. This type of telescope has three mirrors. There's a primary mirror located at the back, which is concave to focus all the light it collects at a point called the focus. Then, a second convex mirror at the front reflects the image back to the primary mirror, which reflects the image to a third mirror that then directs the light to the objective lens. For those interested in studying minor celestial bodies, it's helpful to know the differences between an asteroid, a meteoroid, and a comet.
radio telescope
We completely changed our approach and continued analyzing telescopes, which, while they are indeed telescopes, certainly don't match the telescope images we have. Radio telescopes consist of an antenna that captures electromagnetic radiation corresponding to radio waves, which have wavelengths between 100 microns and 100 kilometers . Instead of capturing light, they capture the radio frequencies emitted by celestial objects. To learn more about how these telescopes gather information, see our entry on what light is.
infrared telescope
Infrared telescopes are instruments capable of capturing electromagnetic radiation in the infrared range, with wavelengths between 15.000 nm and 760-780 nm . This limits the red portion of the visible spectrum, which only detects infrared radiation. These telescopes not only completely eliminate interference from Earth's atmosphere but also provide fascinating information about the "heart" of the galaxy. For more details on the atmospheres of other planets, you can explore our entry on the atmosphere of Uranus and its relationship to telescopes.
x-ray telescope
An X-ray telescope is an instrument that can observe celestial objects that emit electromagnetic radiation in the X-ray spectrum, with wavelengths between 0,01 nm and 10 nm. They allow us to detect objects that don't emit light, but rather what we commonly call radiation, such as black holes. Since Earth's atmosphere prevents these X-rays from space from penetrating, these telescopes must be mounted on satellites. If you're interested in learning more about space exploration, you can read about the Kepler asteroid and the types of telescopes used in the study of celestial objects.
ultraviolet telescope
An ultraviolet telescope, an instrument that allows us to see celestial objects, emits electromagnetic radiation in the ultraviolet spectrum, with wavelengths between 10 and 320 nanometers, making it radiation similar to X-rays. In other words, these telescopes provide invaluable information about the evolution of galaxies and white dwarfs.
Cherenkov telescope
The Cherenkov telescope is an instrument that detects gamma rays from energetic objects such as supernovae or highly active galactic nuclei. Gamma radiation has a wavelength of less than 1 picometer. Currently, there are four such telescopes in the world, and they provide crucial information about the astronomical sources of these gamma rays.
