Astronomy Flashcards
Astronomical unit (AU)
The average distance between the Earth and the Sun.
Parsec (pc)
The distance that gives a parallax angle of 1 arc second
Light year (ly)
The distance light travels in a vacuum in 1 year
Olber’s paradox
For an infinite, uniform and static universe the night sky should be bright not dark because of light received in all directions from stars
Hubble’s Law
The recession speed of distant galaxies is directly proportional to their distance from the observer
Cosmological principle
The universe is homogenous, isotropic and the laws of Physics are the same at all points within it
Critical density
The density of the universe which would cause it to be flat – i.e. the expansion rate would tend towards zero in infinite time.
(Stellar) parallax
The apparent shifting in position of a star relative to the background of distant stars when observed from different positions in the Earth’s orbit round the Sun.
