Transcript Light
A105 Stars and Galaxies Today’s APOD Homework 3 due Sept. 14 EM Radiation Read units 21, 22, 23, 24, 25 News Quiz TODAY Observing the Full Moon Last Thursday Monitoring the Sun with SOHO Orbits between the Sun and Earth, about a million miles away – a constant view of the Sun Sunday Today Applet: RGB What does “electromagnetic” mean? Wavelength and Frequency Properties of waves speed (distance per second) wavelength (length) frequency (cycles per second) speed = wavelength x frequency speed = wavelength x frequency Examples – A Sound Wave Speed – about 340 meters per second Frequency – say, middle C (256-278 cycles per second depending on the scale) What is the wavelength? 340 m/sec = W x 278 per second 340(m / sec) W 1.2(meters) 262(/ sec) speed = wavelength x frequency Example – A Tsunami Wave speed – about 700 km/hour (200 m/sec) Wavelength – about 50 km What is the frequency of the wave? 700 (km/hour) = 50 (km) x frequency frequency = 700/50 = 15 cycles per hour speed = wavelength x frequency Examples – An Electromagnetic Wave speed – 300,000 km per second (3 x 108 meters per second) frequency – say, one billion cycles per second (109 cycles per second) What is the wavelength? What kind of light is this? 3 x 108 m/sec = W x 109 /sec 3x108 (m / sec) W (meters) 0.3(meters) 9 10 (/ sec) X-Rays and Gamma Rays X-rays and gamma rays absorbed in the Earth’s atmosphere Observatories must be sent into space Produced by matter heated to millions of degrees Caused by cosmic explosions, high speed collisions Led to the discovery of black holes in space Allow us to study the hottest regions of the Sun's atmosphere Ultra-Violet Ultraviolet light is blocked by the ozone layer Astronomers use balloons, rockets, and satellites Most stars are too cool to emit much UV light UV sources include very young stars, some very old stars, white dwarfs stars, active galaxies and quasars Discoveries include a hot gaseous halo surrounding our own galaxy that glows in the UV Visible Light • Ground-based observatories “see” during clear sky evenings • Adaptive optics eliminate the blurring effects of the atmosphere • In space we can get a much clearer view of the cosmos • Visible light observations give us the most detailed views of our solar system, and have brought us fantastic images of nebulae and galaxies • Stars are brightest in visible light Infrared Some bands of infrared light can be observed by ground-based observatories To view the rest of the infrared universe we need to use space based observatories or high-flying aircraft Infrared is primarily heat radiation Infrared sees through thick regions of dust in space to peer into star-forming regions and into the central areas of our galaxy Cool stars and cold interstellar clouds which are invisible in optical light are also observed in the infrared • Wavelengths of about 1 mm to 1 m • The cosmic microwave background (electromagnetic radiation left over from the Big Bang) is now observed in the microwave part of the spectrum • Cold interstellar clouds are microwave sources • The early stages of star formation are observed in microwaves Radio • Radio waves are long compared to other EM waves • Most radio radiation reaches the ground and can be detected during the day as well as during the night • Radio telescopes use a large metal dish to collect radio waves • Radio telescopes first detected the radiation left over from the Big Bang • Supernovae, quasars, pulsars, regions of gas between the stars, and interstellar molecules radiate in the radio Multiwavelength Orion Optical X-Ray Infrared UV Radio X-Ray UV Visible The Multiwavelength Sun Radio Infrared Composite Venus Multiwavelength UV Visible Infrared Radio A Mnemonic for the Electromagnetic Spectrum… – – – – – – – Gamma Rays X-rays Ultraviolet Visible Infrared Microwave Radio Really Messy Insane Valentine Unlike (ex) Girlfriend Reindeer Make Interesting Visitors Uttering X-mas Greetings Great X-rated (Unacceptable) Videos In My Room Roy Marches In Very Unique Xray Glasses Randy Makes Interesting Voices Under Xtreme Gasses Exploring Color Astronomy Rules! Astronomy is looking up! Where does light come from? THERMAL EMISSION ATOMIC EMISSION Thermal radiators emit light at all wavelengths Atomic emission occurs only at particular wavelengths Cool matter glows primarily with radio or infrared light All matter glows with light Warmer matter glows with higher energy light Even hotter matter glows blue hot Matter at about 10,000 degrees centigrade glows white hot The glow of matter because of its temperature is called Thermal radiators emit light at all wavelengths Cooler object peak at longer wavelengths (redder) Hotter objects peak at shorter wavelengths (bluer) The higher the temperature, the shorter the peak wavelength Very cool objects peat at radio wavelengths and very hot objects peak at ultraviolet, x-ray, or gamma-ray wavelengths Temperature Matters! • The energy emitted directly proportional to 4 • Temperature • As stars get hotter, their energy output increases quickly! • A star 10 times hotter than Sun has 10x10x10x10 =10,000 times more energy output We need to define TEMPERATURE! • Fahrenheit (used in the U.S.) • Centigrade/Celsius – based on the freezing and boiling points of water – water freezes at 0 C – water boils at 100 C • Kelvin temperature scale – 0 K (-273 centigrade) is the coldest temperature possible (absolute zero) – water freezes at +273 K – water boils at +373 K – room temperature 300 K Hotter thermal radiators are brighter at all wavelengths of light 8000 K Thermal Radiation Curves Brightness is 7000 K 3000 K 6000 K 5000 K 4000 K 300 400 500 600 700 Wavelength (nm) 800 900 1000 Why don’t we glow in the dark? a) People only reflect light. b) People emit infrared light that is invisible to our eyes. c) People are too small to emit enough light for us to see. d) People do not contain enough radioactive material. Finish units 21, 22, 23, 24, 25 E.M. Radiation worksheet due Rooftop session at 8:30 Thurs. Kirkwood Open Night on Weds