20.1 - 20.5 Flashcards
what is the cosmological principle
the assumption that the universe is homogenous and isotropic when viewed on a large enough scale and the laws of physics are universal
what’s an astronomical unit
the mean distance from the earth to the sun
what’s a light year
the distance travelled by light in a vacuum in a time of one year
what’s a parsec
the distance at which a radius of one AU subtends an angle of one arcsecond
what is an arcminute
unit of an angle. 1° = 60 arcminutes
1 arcminute = 60 arcseconds
what is stellar parallax
a technique used to measure the distance of stars from the earth that are less than 100pc away by comparing their position with distance stars 6 months apart
what’s a parallax angle
the angle of the apparent shift in the position of a relatively close star against the backdrop of much more distant stars
what’s the doppler effect
the change in frequency and wavelength of waves received from an object moving relative to the observer compared to what would be observed without relative motion
define ‘blue-shifted’
the shortening of observed wavelengths when the source is moving towards the observer. (causes light to shift towards the blue end of the spectrum)
define ‘red-shifted’
the lengthening of observed wavelengths when the source is moving away from the observer. (causes light to shift towards the red end of the spectrum)
what’s the ‘big bang’
the theory that at a moment in the past all of the matter contained in the universe was in a singularity that expanded rapidly outwards
what’s Hubble’s law
the recessional speed of a galaxy is proportional to its distance from earth
what’s the ‘expanding universe’
the idea that the fabric of space and time is expanding in all directions. therefore any point in the universe is moving away from all other points.
define homogenous
uniform in terms of the distribution of matter across the universe when viewed on a large enough scale
define isotropic
the same in all positions. ( the universe appears the same to an observer regardless of their position)
