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Spectral Lines: Spectral lines correspond to temperature in the 7 different classes of
stars- The coolest stars demonstrate spectral lines of molecules and neutral metals while
the hottest, bluest stars’ source of spectral lines are ionized helium atoms; the hotter the
gas, the faster the molecules or atoms move, the more likely electrons will be disturbed or
disrupted; emission and absorption lines depend on electron orbital structure of atoms.
Star Equilibrium: Main-sequence star equilibrium is determined by individual mass and
chemical compositions. Nuclear reactions result in disturbance of equilibrium, leading the
stellar evolution. Hydrogen-burning lifetime = (mass/luminosity) x 9 billion years, since
larger stars have higher interior temperatures, faster use of nuclear fuel and faster
Nuclear Reactions: Main-sequence stars convert hydrogen to helium.
Doppler Effect: Blue-shifts or red-shifts in stars; by measuring wavelengths, velocities
of stars moving towards or away can be studied; shift in wavelength divided by the
wavelength at rest equals approach or recession speed divided by the velocity of light;
can determine the following basic properties of stars- rotation, atmospheric motions,
circumstellar material and motion; evidence for the expansion of universe.
Measuring tangential velocity: This is the motion of the star perpendicular to the line of
sight, determined from measurements of the distance to the star, and the rate of angular
motion across the sky.
Stellar Forces: Gravity pulls inward on stellar particles, while gas pressure, radiation
pressure and magnetic support push outwards. The balance between pressure and gravity
is called hydrostatic equilibrium.
Wien’s Law: W= 0.00290/T, where W is the wavelength at which the maximum amount
of radiation comes from a body of temperature T. The law has implications for the
prediction of infrared stars or star-nebula complexes.
Inverse Square Law: This is the relation describing any entity, like radiation or gravity,
that varies as 1/r^2, where r is the distance of the entity from source.
Parallax determination: Parallax, the apparent shift in the position of an object caused
by a shift in the observer’s position, gives the distance to the object using trigonometry.