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Lecture 4

AST201 Lecture 4.docx

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David Smith

AST201 Lecture 4 01/22/2014 Light Light = source of most information in astronomy White light is a mix of all colours Spectrum = white light sorted by colour Light is a wave: has wavelength, amplitude, speed and frequency = speed/wavelength Each colour has its own wavelength Units of wavelength: micrometer, nanometer Frequency of light is huge Light +waves of electric and magnetic energy Brightness = (electric amplitude) (2 angular size / 360 = physical size / 2pie distance where size can be separation) Astronomy in the News Rosetta Satellite of the European Space Agency “woke up” on January 20 Launched 2004 March 2 Traveled out near Jupiter’s orbit Began “hibernation” in June 201 Will rendezvous with a comet in May Will place a lander on the comet, sample it’s matter and drill a hole 20 cm deep into its surface Will travel with the comet as it orbits in around the Sun and heads back out into the solar system The Full spectrum of Radiation We only see visible light “Radio” – wavelength 1m and longer frequency = 3 x 10 *8 Hz and less Microwave – wavelength about 1 cm Infrared – wavelength about 10 um Visible – wavelength about 500nm Ultraviolet – wavelength about 200 nm X-rays – wavelength about 1nm (surprise awarded nobel prize) “Gamma (y) rays” – wavelength less than about 0.01 nm Golden Age of Astronomy Before about 1950, astronomy used only visible light (See by eye and take photographs) Since 1950, astronomy has had the technology to use all forms of radiation Produced flood of information is received from using all the forms of radiation the most rapid advances in the history of astronomy = Golden Age previous golden age was in the 60s with Galilleo Telescopes Fermi Swift Chandra Hubble (25 years) Spitzer WMAP Other Properties of Light Light = electromagnetic wave Light is also a particle = “photon” Light is both a wave and photon at the same time Photon’s energy depends on wave’s frequency Radio wave = low energy photons (why we can use Wi-Fi/cell phones safely) Gamma rays = high energy photons (why radioactive material is dangerous) See electromagnetic spectrum* Brightness of light depend
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