Frame of reference: A system of coordinates that enables the positions of various objects to be specified.
Alternatively = A system of coordinates that enables measurements to be made (if you know position then you can measure and vice versa)
Galilean Transformation: Transformations made under the assumptions that time measurements and space measurements are independent of the observer
Proper Time : is the time as measured in a frame where the events take place at the same point in space. It turns out to be the shortest possible time that any observer could correctly record for the event.
Astrophysics
Chadrasekhar Limit = mass after which a white dwarf does not form. Equivalent to 1.4 solar masses.
(The heavy mass causes the star collapse into itself to form a neutron star)
Openheimer-Volkoff Limit = a neutron star is stable up to this mass which is equivalent to 3 solar masses, beyond this point and it forms a blackhole.
Luminosity: the total energy emitted by the star per second.
Apparent Brightness: The incident power per unit area received on the surface of the Earth
Apparent Magnitude: A measure of how bright an object appears from Earth
(Good to know but not needed in answer: it is a comparative scale)
Absolute Magnitude: The apparent magnitude when observed at a distance of 10 parsecs
Alternatively: a measure of how bright the object appears from 10 parsecs away. (I recommend the first definition using apparent magnitude...easier to remember)
