When you think of telescopes, what do you think of? A long tube that astronomers look through to see the stars on a dark night? That’s true. But it’s only one type of telescope. There are telescopes on the ground, in the sky, and in space. They are watching the planets, stars, and galaxies all the time. Show
Astronomers used to work really hard to document it all with the naked eye. But the human eye isn't so great at picking out the details of dim and distant objects, even on a clear night. What humans needed was a tool to help make far away things look closer and brighter. Enter the optical telescope. Who invented the optical telescope?
Galileo did not invent the telescope. But within one year, he had greatly improved on Lippershey’s design. He promoted his own telescopes. He also observed Jupiter’s largest moons. These are the reasons why, when many people hear the words “invention of the telescope,” they think of Galileo! How do optical telescopes work?Let's consider a basic optical telescope. If you were looking to buy a telescope for yourself, you would learn that there are two basic designs:
A refractor uses lenses within a tube to refract (bend) light. It's the type of long telescope which you might imagine old-time astronomers, like Galileo, using. Reflectors, on the other hand, use mirrors instead of lenses to reflect light. What are the parts of a telescope?
A classical Newtonian reflector also has a long tube. But instead of an objective lens, it has an objective or primary mirror. Remember, an objective lens is at the end of the tube where the light comes in. In contrast, the mirror is at the opposite end of the tube. How does light travel in each type of telescope?
In a reflector, light enters the telescope at the end opposite the primary mirror. The mirror is a concave mirror. Similar to a convex lens, a concave mirror converges the light at the secondary mirror. The rays of light converge at the focal point. At this point they again begin to diverge. The convex lens in the eyepiece takes the converging light and straightens it back out. As with the refractor, the image is still upside down. It appears as a virtual image beyond the telescope in the direction the person is looking. Path of light rays through a reflecting telescope (©2019 Let’s Talk Science based on an image by Krishnavedala [CC BY-SA 4.0] via Wikimedia Commons).Remember how we said lenses in a refractor telescope would be heavy? Well, mirrors are less heavy than lenses. That’s why people have been able to build very large reflecting telescopes. Why are telescopes in observatories so big?
What if I only have a small telescope?
ReferencesAbel, P. G. (2015, October). Absolute beginners no. 3: A short introduction to some common types of telescope. British Astronomical Association. Helden, A. V. (1995). The telescope. The Galileo Project. McFadden, C. (2018, May 27). A brief history of the telescope: From 1608 to gamma-rays. Interesting Engineering. What do reflecting telescopes detect?Reflectors are used not only to examine the visible region of the electromagnetic spectrum but also to explore both the shorter- and longer-wavelength regions adjacent to it (i.e., the ultraviolet and the infrared).
How do reflecting telescopes make distant objects appear closer?Reflecting telescopes are sometimes called Newtonian telescopes after their inventor Isaac Newton who built the first one in 1668. They use mirrors to collect and focus the light towards the eyepiece. Mirrors are lighter than lenses and they are also easier to shape into a smooth and perfect surface.
What is the most important thing a telescope does to make it easier to see dim stars?The most important aspect of any telescope is its aperture, the diameter of its main optical component, which can be either a lens or a mirror. A scope's aperture determines both its light-gathering ability (how bright the image appears) and its resolving power (how sharp the image appears).
How does a reflecting optical telescope work?Reflecting telescopes use mirrors instead of lenses to reflect light to a focal point. Reflectors have two mirrors. The primary mirror is the big curved mirror at the back of the tube that begins to focus the light. The secondary mirror is the smaller mirror at the front of the tube.
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