* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Comparing Earth, Sun and Jupiter
Survey
Document related concepts
Observational astronomy wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Outer space wikipedia , lookup
Dyson sphere wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Stellar kinematics wikipedia , lookup
Timeline of astronomy wikipedia , lookup
H II region wikipedia , lookup
Planetary habitability wikipedia , lookup
Future of an expanding universe wikipedia , lookup
Extraterrestrial atmosphere wikipedia , lookup
Type II supernova wikipedia , lookup
Hayashi track wikipedia , lookup
Stellar evolution wikipedia , lookup
Transcript
Stars Stars have a range of intrinsic luminosities and temperatures (colour) Correlations between colour and luminosity tell the story of stellar evolution. The Solar luminosity is 3.8x1026 J/s This is enough energy to melt a block of ice 1AUx1kmx1km in only 0.1 s. If the luminosity of the Sun has been approximately constant, the total energy released since its formation would be 4.8x1043 J. The surface temperature of the sun is about 5700 K The central temperature is inferred to be much higher: about 10 million K This means the Sun is a fairly ordinary, main sequence star. Stellar Structure Gas pressure in the stellar interior opposes gravity to keep the star in equilibrium The equation of hydrostatic equilibrium equates the pressure gradient to the gas density. dP GM r dr r2 The gas density and enclosed mass are related by the conservation of mass: dM r 4r 2 dr The density, pressure and temperature are related by the equation of state, which can usually be approximated as the ideal gas law. kT P nkT where n is the number density mH and r is the mass density of the gas and is the mean molecular weight. Stellar luminosity The energy production in main-sequence stars is due to the fusion of hydrogen into helium in the core This is the only process that can produce sufficient energy Classically fusion would not be efficient enough: requires quantum mechanics (barrier tunneling). Energy is transported to the surface via either radiation or convection. The Sun has a convective envelope and radiative interior. Low mass main-sequence stars are entirely convective. More massive stars are much more luminous (the fusion reactions release much more energy) Therefore they burn their core mass more quickly, and have shorter main sequence lifetimes. The Solar atmosphere The light we see from the Sun is emitted from the photosphere. The atmosphere extends thousands of kilometers above this. In general the atmosphere is very low density, but much higher temperature. Different parts of the Sun are visible at different wavelengths: X-ray: All emitted from the million-degree corona Show a very stormy and dynamic atmosphere, the source of the solar wind Ultraviolet: UV radiation comes from the chromosphere, between the photosphere and corona Infrared: Long-wavelength radiation from the chromosphere and corona Dark spots caused by absorption of light due to denser gas in the atmosphere. Radio: Emitted near the transition region between the chromosphere and corona