Chapter 21: Stars, Galaxies, Universe Section 1: telescopes Key concepts: What are the regions of the electromagnetic spectrum? What are telescopes and how do they work? Where are most large telescopes located? Key terms: Telescope, electromagnetic radiation, visible light, wavelength, spectrum, optical telescope, refracting telescope, convex lens, reflecting telescope, radio telescope, observatory

Telescopes A telescope is a device that makes distance objects appear closer. Galileo was not the first to use a telescope, but he helped make it famous.

Electromagnetic radiation Electromagnetic radiation is a form of energy that can travel through space in the form of waves. Visible light is an example of electromagnetic radiation. Other forms: radio, infrared, ultraviolet, x-rays, gamma (listed from long wavelength to short wavelength) Wait, what’s a wavelength???

http://www.youtube.com/watch?v=snNwE6txxP0

Electromagnetic spectrum Wavelength – distance between the crest (high point) of a wave and the crest of the next wave Spectrum – range of light colors with different wavelengths Radio, infrared, visible light, ultraviolet, x-rays, gamma ROYGBIV What kinds of radiation do you experience every day?

Types of telescopes Telescopes are instruments that collect and focus light and other forms of electromagnetic radiation. Optical telescopes – telescope that uses lenses or mirrors to collect and focus visible light Two major kinds: refracting and reflecting

Refracting telescopes Uses convex lens to gather and focus light Convex lens is a piece of transparent glass, curved so that the middle is thicker than the edges Light enters the telescope through a large objective lens at the top. It focuses the light at a certain distance (focal length). The larger the lens, the more light collected. The smaller lens at the lower end of the telescope is the eyepiece lens. It magnifies the image produced by the objective lens.

Reflecting telescope Uses a curved mirror to collect and focus light. The curved mirror in a reflecting telescope focuses a large amount of light into a small area (just like the refracting telescope). The largest telescopes are all reflecting telescopes.

Radio telescope Used to detect radio waves from objects in space. Most have curved, reflecting surfaces. They focus radio waves the same way a mirror focuses light waves. The larger it is, the more waves it can collect.

Other telescopes Can detect infrared, uv, x rays, gamma rays Many large optical telescopes are equipped with systems that improve the quality of the images. They use computers and lasers.

Observatories Observatories are buildings that contain one or more telescopes. Many are located on mountains or in space. Earth’s atmosphere makes stuff in space look blurry, so putting an optical telescope on a mountaintop eliminates some light from the cities and the sky is clearer. Radio telescopes do not need to be put on mountaintops.

Telescopes in space Hubble Space Telescope is a reflecting telescope with a mirror 2.4 meters in diameter (big big big). It orbits Earth above the atmosphere, so it can produce very detailed images. Hottest objects in space give off x rays. Some telescopes pick these up, like the Chandra X ray observatory. 2003 – NASA launched Spitzer Space Telescope – measures infrared.