Transcript March 4
Survey of the Universe Tom Burbine [email protected] Prospective Astronomy Majors Lunch Monday, March 4th 12:15-1:10pm Kendade 303 Meet the faculty, learn about the Mars Rover, and enjoy a delicious lunch. HW# 3 • Due Wednesday So why are some types of radiation dangerous? • Higher the energy, the farther the photons can penetrate • So gamma and X-rays can pass much more easily into your the body • These high-energy photons can ionize atoms in cells • Ionization means removes electrons from an atom Thermal energy • Temperature – average kinetic energy of particles • Higher temperature – more kinetic energy, particles moving faster • For examples, air molecules around you are moving at ~500 m/s Temperature scales • • • • • • In America, we use Fahrenheit Water freezes at 32 degrees F Water boils at 212 degrees F Everywhere else, they use Celsius Water freezes at 0 degrees C Water boils at 100 degrees C In Science • Temperature is measured in Kelvin • Zero Kelvin is absolute zero – nothing moves • Add 273.15 to the Celsius temperature to get the Kelvin temperature • 273.15 Kelvin = 0 degrees Celsius Blackbody • A black body is an object that absorbs all electromagnetic radiation that falls onto it. • Perfect emitter of radiation • Radiates energy at every wavelength http://www.astro.ncu.edu.tw/contents/faculty/wp_chen/Ast101/blackbody_curves.jpg http://www.rap.ucar.edu/general/asap-2005/Thur-AM2/Williams_DoD_Satellites_files/slide0005_image020.gif Wien’s Law • Wavelength of Maximum intensity of the blackbody curve peak = (2,900,000) nm T (Kelvin) • If T = 10,000 K, • λmax = [2,900,000/(10,000)] nm • λmax = 290 nm • 1 nanometer = 1 x 10-9 meters • λmax = 290 nm = 2.0 x 10-7 meters Power and Luminosity • Power is in Joules/second = Watts • Luminosity is the total light output Stefan-Boltzman Law • Emitted power per square meter of the surface = σT4 • Temperature is in Kelvin • constant is σ = 5.67 x 10-8 Watt/(m2K4) • If you double the temperature of an object, it will be 2*2*2*2 = 16 times more luminous • If you triple the temperature, it will be 3*3*3*3 = 81 times more luminous • Hotter objects are more luminous (give off more light) • The luminosity of a blackbody rises as the temperature to the fourth power What we can learn from stars • Luminosity (emitted energy/second) of an star is proportional to T4 and the surface area of the star L= σAT4 (σ =5.67 × 10−8 W m−2 K−4) • The color of the star is related to 1/T Wavelength peak = [2,900,000 /T (Kelvin)] nm 1 nanometer = 1 x 10-9 meters • Spectral lines give you information of the composition of the star Any Questions?