How does a telescope work?
Galileo Galilei didn’t invent the telescope. Even so, it was when the great Italian scientist pointed a telescope toward the night (and even the day) sky that the world changed forever. Galileo discovered the planet Venus has phases, just like the Moon. No one could have known that until the telescope was invented. Galileo saw that the Moon had craters and mountains, and that the Sun had moving black spots on its face. He also discovered four new moons circling the planet Jupiter. All these discoveries helped show that the Earth is not the centre of the universe, that the planets orbit a changing and imperfect Sun, and that the planets are other worlds, something like the Earth but very far away. With his telescope, Galileo literally remade the world. Galileo’s telescope was a refracting telescope. Isaac Newton, who was born the same day Galileo died, invented another kind of telescope, called a reflecting telescope. Reflecting telescopes use mirrors instead of lenses to make faraway t
A refracting telescope is a long tube with a convex lens at one end and an eyepiece at the other. Light comes in through the convex lens and is condensed or refracted toward the eyepiece. There the image is magnified. A reflecting telescope uses a curved or concave primary mirror at the rear of the telescope. Light is collected by the mirror and is reflected back up the telescope tube until it reaches a secondary mirror set at a 45º angle. The image is then reflected out through the side of the telescope where it passes through a concave lens or eyepiece. Cassegrain’s telescope is similar to Newton’s but it uses a convex mirror to reflect the image back down the tube to come out through a hole in the centre of the primary mirror, where it is received in the eyepiece. The benefit of Newton’s and Cassegrain’s telescope compared to Galilieo’s is that mirrors can be made much larger than the lenses in Galileo’s design, and so, much larger telescopes can be built. The largest refracting tel
Basically, a telescope is a long tube with magnifying lenses at both ends. The end you put to your eye has two convex (curved outward) lenses, which magnify the image. At the far end of the telescope is a concave (curved inward) lens which draws in the light. The distance between these two sets of lenses can be changed to focus
This is the basic principle of a telescope: it lets you see distant objects clearly, by making the image bigger. How is this done? We can find the beginnings of our answer in the humble magnifying glass; notice that when you look at an object through a magnifying glass, it appears bigger. That’s because a magnifying glass uses a convex lens (a lens whose middle is thicker than its sides) to focus the light from the object into your eye, and thus it makes the image appear larger. Now there’s a small problem with this method; beyond a certain distance (the focal length, or f) the virtual image created by the lens will appear smaller and upside down. The main remedy for this is to use another lens to turn the image right side up again, and magnify it. In this two-lens arrangement, the main, big lens is called the objective lens, and the lens that turns the image right side up is called the eye lens. This arrangement is common in smaller telescopes, where one can adjust the focus of the te
A telescope collects light from a distant object and focuses it to form an image of the object. When the image is recorded, an observation is made. Originally, the only way to record the image was by hand — astronomers would make a drawing of what they saw through their telescopes. In the 1800s, photography was invented and astronomers experimented with making photographs through their telescopes. In the early 20th century, astronomers started specifically designing and building telescopes to record the image on photographic plates. The 1980s saw the invention of charge-coupled devices (CCDs) that allow the image to be recorded digitally. By the end of the 20th century, all research telescopes would use CCDs to make observations.
