2How do Astronomers know what they know? Almost everything we know about Astronomy was learned by gathering and studying light from distant sourcesProperties of lightBehaves like a wave; has wavelength (distance from crest to crest)Visible light can be separated into distinct wavelengths by a prismRadio waves = a few km Gamma rays = less than a billionth of a cmBehaves like a particle; photons – small packet of light energyPhotons from the sun push the tail of a comet away.Light with shorter wavelengths have more energetic photons!
3Electromagnetic Spectrum Electromagnetic Radiation(EMR) - the flow of energy at the speed of light in the form of the electric and magnetic fields.Radio waves, infrared, visible light, ultraviolet, x-rays, and gamma raysElectromagnetic spectrum – arrangement of EMR according to their wavelengths and frequenciesMost wavelengths are too long or short for us to seeContinuous spectrum A spectrum of radiation distributed over an uninterrupted range of wavelengths.
4Absorption vs. Emission Spectrum Emission spectrum – a series of bright lines of particular wavelengths produced by a hot gas under low pressureAbsorption spectrum – “dark line spectrum,” produced when white light passes through a gas and certain wavelengths of light are absorbedMost often used by astronomers to identify stars.The specific wavelengths of absorption spectral lines of stars are like “fingerprints” used to identify the elements present in the star
7The Doppler EffectDoppler effect – the perceived change in wavelength of a wave that is emitted from a source that is moving away or toward an objectIf the source of light is moving away from you the wavelength will stretch and cause a Red ShiftIf the source of light is moving toward you the wavelength is compressed and causes a Blue Shift
8Tools For Studying Space Telescopes are used to gather and collect the radiant energy from distant galaxies and starsTypes of telescopesOptical telescopes – contain mirrors or lenses, collect visible lightRadio telescopes – giant radar dishes that detect radio wavesSpace telescopes – orbit above Earth’s atmosphere to produce clearer images
9Optical Telescopes: Properties Light-gathering power – ability to intercept more light from distant objects, which means brighter imageslarger lens or mirror = “see” fartherResolving power – allows for sharper images and finer detaillarger lens or mirror = sharper imageMagnifying power – ability to make an image larger, depends on focal lengths of the objective and eyepiecechange the eyepiece = change the magnifying powerMoral of the story When it comes to telescopes, size does matter
10Optical Telescopes: Refracting Refracting telescope – uses a lens to bend lightThe objective lens produces an image by bending light from distant objects so that light converges on a focal pointChromatic 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
11Optical Telescopes: Reflecting Reflecting telescope – uses a concave mirror to focus lightAdvantages = don’t need to be optical quality, can be supported from behind the mirror, can be made much largerDisadvantage = secondary mirror blocks some light, solution… make it bigger!
12Radio TelescopesThe dish of the radio telescope focuses the radio waves on an antenna, transmits it to an amplifierInterferometer - several radio telescopes linked togetherAdvantages = can run all day every day, cheaper to build, can detect clouds of gas to cool to emit visible lightDisadvantages = take up a lot of space, hindered by human-made radio interference
13Space Telescopes James Webb Gotchu?! Hubble Space Telescope was the first of its kindUsed to study everything from birth of stars to extrasolar planetsChandra X-ray ObservatoryStudies black holes by collecting X-RaysNASA plans to launch the James Webb Space Telescope in 2013 to study infrared radiationJames Webb Gotchu?!