Today we know what our neighboring worlds look like, we know how beautiful the universe is, we have seen spectacular supernova explosions and have witnessed the first images of a black hole. All thanks to the telescope! Without a doubt, telescopes have become the most used tools in astronomy and astrophysics. Anyone who wants to do research in this area has needed a telescope at one time or another. This article is intended to help you better understand this wonderful device.
Telescopes have really helped discover our place in the universe. In the past, captains and pirates often used telescopes with only 4x magnification and a very narrow field of view. However, today’s telescopes are giant chains of glasses, capable of observing every corner of the universe. Telescopes act as our enhanced eyes and help us observe things that the naked eye cannot see.
Telescopes are indispensable tools for amateur astronomers and those who love the beauty of the night sky. Photo: PicsWe
Technically, a telescope is an optical device capable of magnifying images of distant objects using a system of glasses and spherical mirrors arranged in a certain order. The term “telescope” generally refers to optical telescopes, but these have undergone major changes since their introduction in the 17th century. This is why we have many types of telescopes today. The literature operates on different wavelength ranges, from radio waves to gamma rays. . The main purpose of a telescope is to collect light and radiation emitted by distant objects and focus them onto a focal point, where the images can be observed, photographed or studied.
Brief history of telescopes
Hans Lippershey. Photo: Secretsofuniverse.in
The first telescope* was built around 400 years ago, more precisely in 1608, by a Dutch eyeglass maker named Hans Lippershey. Even though Lippershey did not claim the patent, news of his new invention spread like wildfire across Europe. Lippershey’s design essentially consists of a convex objective lens and a concave eyepiece. This device has the ability to magnify objects 3 times compared to the original magnifying glass.
When Galileo Galilei heard about Hans Lippershey’s telescope in 1609, he immediately began designing it without even looking at Hans’s equipment. It has significantly improved the capabilities of the telescope and achieved 20x magnification. Additionally, Galileo became the first person to point a telescope at the sky and discovered Jupiter’s four largest moons in 1610.
Galileo Galilei presents the telescope he built. Source: All About History
Classification of telescopes
There are many types of telescopes. At the same time, there are many ways to classify: depending on the arrangement of lenses and mirrors; depending on the type of radiation that the glass receives; depending on the external conditions they can withstand, etc. But there are three basic types of telescopes, a source for the development of more advanced versions. The three types are:
Refractor telescope (refractor) – The first telescope developed was a refractor. Refracting telescopes use a lens to collect and focus light. Lenses are placed in front of the telescope and light is bent (refracted) as it passes through these lenses. Most people starting out in astronomy will use refractors because they are easy to use and require less maintenance than other types.
Diagram illustrating the structure of a refracting telescope. Photo: reddit.com, HowStuffWorks
Reflecting telescope (reflector) – Reflective glass uses mirrors to collect and concentrate light. All celestial bodies are so far away that the light they emit and reaches Earth is made up of parallel rays of light. Because the light rays are parallel to each other, the mirror of the reflecting telescope is transformed into a parabolic curve so that it can focus the parallel light rays into a single point. All research telescopes and major amateur telescopes today are reflectors because they have superior advantages over refractors.
Diagram illustrating the structure of a reflecting telescope. Photo: Liverpool Astronomical Society (LAS)
Compound/Combined Telescope (Compound/catadioptric telescopes) – Compound telescopes can be considered a “hybrid” between a reflecting telescope and a refraction telescope. They combine the best features of both types.
Diagram illustrating the structure of a combined telescope. Photo: Abrams Planetarium
Basic terminology related to telescopes
Objective (Objective) – The objective placed in front is called objective or primary objective. It collects light from distant objects and concentrates it into a single point.
Opening (Aperture) – The diameter of the primary mirror/lens is called aperture. The larger the aperture, the brighter the image formed. A good amateur telescope generally has an aperture of 80 to 300 mm. Meanwhile, some large professional telescopes, worth billions of dollars, have mirror apertures of up to 10 meters.
Focal distance (Focal Length) – When hitting the mirror or passing through the lens, the light will be adjusted to focus on the focal point of the farthest plane. The distance between the center of a spherical lens or mirror and its focus is called focal length.
Ocular (Eyepiece) – Eyepiece refers to a small tube containing lenses whose task is to create the final image that the observer can see. Telescopes usually have at least two eyepieces: one for low magnification and a second for higher magnification.
Some eyepieces. Photo: stargazerslounge.com
Exaggerated capacity (Magnifying Power) – This parameter tells us the telescope’s ability to increase the apparent size of the observed object. Magnification can be determined by dividing the focal length of the telescope (i.e. objective) by the focal length of the eyepiece. Thus, the greater the focal length of the eyepiece, the lower the magnification obtained, but the resulting image is brighter.
Telescope is translated in Vietnamese as telescope or telescope. For the purposes of this article, a telescope is called a telescope when it is not used for the purpose of observing the sky. Therefore, when we refer to Hans Premiership’s invention, we use the word “telescope”, and when we refer to Galileo Galilei, we use the word “telescope”.
Earthgrazer – Hanoi Amateur Astronomy Society (HAS)