38 Powerful Telescopes-Mid

Powerful Telescopes FOCUS Question How do telescopes help us see far into the universe?

Looking into Space Are there planets outside our solar system? What are stars made of? Is there a black hole at the center of the Milky Way galaxy? How big is the universe? Astronomers rely on a very important type of tool to help answer these questions: the telescope. Telescopes allow us to see distant objects They magnify these objects. so that they appear bigger than they do when you look at them with the naked eye. There are many different types of telescopes. Some use mirrors to collect light, while others use glass lenses. Some collect visible light, while others detect light that we can't see. Some make observations from Earth, while others are out in space.

Refracting Telescopes The first known telescope was invented in 1608. In 1609, Thomas Harriot and Galileo Galilei used telescopes to look into the sky. They were amazed at what they saw. Harriot drew maps of the Moon with details not seen before. Galileo discovered four moons orbiting the planet Jupiter. Soon, scientists were building more powerful telescopes to observe objects in the sky. Galileo's telescope was a refracting telescope. In a refracting telescope, light first travels. through a piece of curved glass called a lens The curve of the lens. causes the light to bend, or refract. Light rays pass through a tube, come together, and pass through a second lens. The second lens refracts the light again before it passes into the eye. The eye sees a large image of the object.

Reflecting Telescopes Early refracting telescopes had some problems. It was hard to grind the glass lenses perfectly, so the images were often fuzzy and the colors were not quite right. In 1668, Isaac Newton invented the reflecting telescope. These telescopes use mirrors instead of lenses to gather light. In a reflecting telescope, light from the object travels through the telescope and reflects, or bounces off, a curved mirror. The curved mirror focuses light to a small point, where there is another, smaller mirror. The light then bounces off that mirror and travels to the eye. Most large modern telescopes are reflecting telescopes. Compare the telescope diagrams on pages 3 and 4.

Invisible Forms of Light Objects in space give off many different forms of light, or electromagnetic radiation. We can see visible light, but we can't see the other forms of light. These include radio waves microwaves, infrared, ultraviolet, X-rays, and gamma rays. Engineers have designed telescopes that detect these invisible forms of light. For example, the Goldstone radio telescope in California collects radio waves from space. Radio telescopes help us search for signs of intelligent life in the universe. The image to the right is from the Chandra X-Ray Observatory in space. It shows X-rays from an exploding star called Kepler's Supernova. The image uses false colors. Each color represents a different X-ray wavelength.

Earth-Based Telescopes: The Bigger, the Better Increasing the size of a telescope's mirror usually leads to a more powerful telescope. Bigger reflectors gather more light. They allow us to see objects that are much smaller, fainter, or farther away than smaller telescopes do. However, it is very hard to make large mirrors that are perfectly shaped. Also, their weight causes them to bend. Then the light does not bounce off the surfaces in the right direction. The images become distorted. To avoid this problem, engineers often make mirrors that are actually many smaller mirrors put together. The large mirror of the Southern African Large Telescope (SALT) is made of 91 mirrors, each of which is 1.2 meters (4 ft.) across Together, they make a mirror that is 11 meters (36 ft.) by 9.8 meters (32 ft.) It can help us see objects that are one billion times fainter than what you can see when you look at the sky.