Temperature • Temperature is a measure of the average kinetic energy of the particles in a gas. • The faster particles are moving, the more energy they have, and the higher the temperature. • Astronomers use the Kelvin temperature scale to express the temperature of stars. 0 Kelvin = -273.2 C = -459.7 F
Starlight • The light weseefrom a star comes fromthephotosphere (outersurface). • Thetemperature of thephotosphereiswhatastronomersmeasure. • Black BodyRadiationreferstothe EMR emittedby a heatedobject, like a starorlightbulb. • Hotter objects emit more black body radiation than cooler objects.
Temperature vs Wavelength • The wavelength of the photon emitted during a collision between particles depends on the violence of the collision. • Short wavelength, high energy photons are emitted during a violent collision. These are rare. • Extremely gentle collisions are also rare. • The wavelength of maximum intensity (max) is the wavelength at which an object emits the most radiation.
Intensity vs Wavelength • The wavelength of max intensity depends on temperature. • The wavelength of max intensity is shorter for hotter stars. • Temperature determines color… hotter stars are more blue and cooler stars are more red.
Radiation Laws • Energy • Stefan-Boltzmann Law E = T4 E is energy in Joules = 5.67 E-8 T is temperature • Color • Wien’s Law max = 3,000,000 T is in nanometers T is temperature
Assignment • Pg. 158 Review Questions #1,2,3,6,8 • Pg. 158 Problems #1 – 5 (Show your work)
Balmer Absorption Lines • The temperature of a star can be found using Balmer absorption lines. • These lines are produced by atoms with electrons in the 2nd energy level of the electron cloud.
Low temperature stars • relatively non-violent collisions, • electrons mostly in ground state, • low energy, • longer wavelengths, • weak Balmer absorption lines
High temperature stars (20,000 K and above)… • More violent collisions, • Electrons changing energy levels, some forming ions, • High energy, • Shorter wavelengths, • Weak Balmer absorption lines because electrons are excited and in higher orbits
Mid-temperature stars (about 10,000 K)… • Collisions just right to have electrons in the 2nd energy level, • Balmer lines are strong
Spectral Classification • The strength of spectral lines depends on temperature. • All stars of the same temperature will have a similar pattern of spectral lines. • There are 7 major spectral classes or types: O, B, A, F, G, K, M
Spectral Sequence • “O” type stars are the hottest and “M” type are the coolest • Stars are classified by the lines and bands in its spectrum.
Intensity vs Wavelength • Absorption lines appear as sharp dips. • Hydrogen Balmer lines are the strongest in type A subclass 0 stars. • Ionized Calcium is strong in type K stars. • Titanium oxide is strongest in the cooler stars.
New Spectral Types • Astronomers have found 2 new classes of stars that are cooler than the “M” type: L and T. • The development of larger telescopes and infrared cameras helped to find these new types of stars.