Chapter 21: Stars, Galaxies, UniverseSection 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.