Chapter 24: Studying the Stars

1. Hubble Gotchu! Chapter 24: Studying the Stars Astronomy Mr. Steinken Pgs. 673 - 683

2. How do Astronomers know what they know? • Almost everything we know about Astronomy was learned by gathering and studying light from distant sources • Properties of light • Behaves like a wave; has wavelength (distance from crest to crest) • Visible light can be separated by a prism • Radio waves = a few km Gamma rays = less than a billionth of a cm • Behaves like a particle; photons – small packet of light energy • Photons from the sun push on vaporized gas from a comet and form the tail • Light with shorter wavelengths have more energetic photons!

3. Electromagnetic Spectrum • Electromagnetic Radiation(EMR) - radio waves, infrared, visible light, ultraviolet, x-rays, and gamma rays • Electromagnetic spectrum – arrangement of EMR according to their wavelengths and frequencies • Most wavelengths of the EMR are to long or short for us to see  Continuous spectrum –uninterrupted band of color emitted by an incandescent solid, liquid or gas

4. Absorption vs. Emission Spectrum • Absorption spectrum – “dark line spectrum,” white light is passed through a gas and certain wavelengths of light are absorbed • Emission spectrum – a series of bright lines of particular wavelengths produced by a hot gas under low pressure • Absorption spectral lines of stars are like “fingerprints” used to identify the elements present in the star

6. The Doppler Effect • Doppler effect – the perceived change in wavelength of a wave that is emitted from a source that is moving away or toward an object • If the source of light is moving away from you the wavelength will stretch and cause a Red Shift • If the source of light is moving toward you the wavelength is compressed and causes a Blue Shift

7. Tools For Studying Space • Telescopes are used to gather and collect the radiant energy from distant galaxies and stars • Types of telescopes • Optical telescopes – contain mirrors or lenses, collect visible light • Radio telescopes – giant radar dishes that detect radio waves • Space telescopes – orbit above Earth’s atmosphere to produce clearer images

8. Optical Telescopes: Properties • Light-gathering power – ability to intercept more light from distant objects, which means brighter images larger lens or mirror = “see” farther • Resolving power – allows for sharper images and finer detail larger lens or mirror = sharper image • Magnifying power – ability to make an image larger, depends on focal lengths of the objective and eyepiece Moral of the story  When it comes to telescopes, size does matter

9. Optical Telescopes: Refracting • Refracting telescope – uses a lens to bend light • The objective lens produces an image by bending light from distant objects so that light converges on a focal point Chromatic aberration – light of different colors are focused at different locations; when red light is focused there is a blue halo, when blue light is focused there is a red halo

10. Optical Telescopes: Reflecting • Reflecting telescope – uses a concave mirror to focus light • Advantages = don’t need to be optical quality, can be supported from behind the mirror, can be made much larger • Disadvantage = secondary mirror blocks some light, solution = make it bigger!

11. Radio Telescopes • The dish of the radio telescope focuses the radio waves on an antenna, transmits it to an amplifier • Interferometer - several radio telescopes linked together Advantages = can run all day every day, cheaper to build, can detect clouds of gas to cool to emit visible light Disadvantages = take up a lot of space, hindered by human-made radio interference

12. Space Telescopes • Hubble Space Telescope was the first of its kind • Used to study everything from birth of stars to extrasolar planets • Chandra X-ray Observatory • Studies black holes by collecting X-Rays • NASA plans to launch the James Webb Space Telescope in 2013 to study infrared radiation James Webb Gotchu?!