Astronomy, Cosmology and Special Relativity Flashcards
Black Body
A perfect absorber/emitter of energy.
Thermal equilibrium (such as for a black body)
The power being absorbed is equal to the power being radiated out.
Parsec
The distance to an object that has a parallax angle of 1 arcsecond when it has moved by 1 astronomical unit.
Cepheid Variables
These are stars that undergo periodic contractions and expansions, causing their luminosity to vary substantially. The period of these contractions/expansions is logarithmically related to the star’s luminosity, allowing for the distance to that star to be calculated.
Type 1A Supernovae
These supernovae are caused by binary star systems that include a white dwarf. The white dwarf accretes (matter streams to the white dwarf from) the other star (e.g. a red giant) and eventually explodes when it reaches a certain mass. Since they always explode at the same mass, the resulting light curve always follows the same pattern and has the same peak luminosity.
Standard Candles
Standard Candles have a known absolute magnitude (and thus luminosity) so can by comparing the measured apparent magnitude (and thus luminous flux) of the standard candle we can work out the distance (using the flux equation).
Hubble’s Law
The recessional velocity of a distant galaxy is directly proportional to its distance away from us.
Redshift
The expansion of space includes the stretching of light itself, increasing its wavelength. These means that light from distant galaxies is shifted towards longer wavelengths.
Inertial Reference Frame (Optional)
A frame in which Newton’s first law applies, i.e. it is not accelerating relative to another frame.
Postulates of Special Relativity (Optional)
- The laws of physics are the same in all inertial reference frames.
- The speed of light in free space is invariant.
