5.5.3: Cosmology Flashcards
(18 cards)
Astronomical unit
The mean distance between the Earth and the Sun
Lightyear
The distance that light will travel in a vacuum in one year
1 arcminute
1/60 of a degree
1 arcsecond
1/60 of an arcminute
1/3600 of a degree
Parallax angle
The angle of apparent shift when a relatively close star is viewed from two different positions when viewed against a background of distant stars
Parsec
The distance at which 1 AU subtends an angle of 1 arcsecond
Isotropic
The Universe looks the same in all directions
Homogeneous universe
Matter is distributed uniformly throughout the Universe
Cosmological principle
When viewed at a large enough scale, the Universe is isotropic, homogeneous and the laws of physics are the same everywhere
Doppler effect
The change in frequency and wavelength of a wave due to relative motion between the source and the observer
Blue-shift
When the observed wavelengths appear shorter due to the source moving towards the observer
Red-shift
When observed wavelengths appear longer due to the source moving away from the observer
Hubble’s law
The recessional speed of galaxies is approximately proportional to their distance from Earth
Cosmic microwave background radiation
The microwave signal detected at constant intensity in all direction from Earth with a black body profile of 2.7 Kelvin
Age of universe
1/Ho if we assume the Universe has expanded uniformly since the Big Bang
Inflation
A very short period of very large expansion of the universe at 10^-35 seconds after the Big Bang
Dark matter
A theoretical substance that doesn’t emits or absorb light. It is the proposed source of the additional gravity needed to explain the difference in observed and predicted star velocities in galaxies. Estimated to account for ~27% of the Universe
Dark energy
A theoretical energy that fills all space and is the proposed cause of the accelerating expansion of the Universe. Estimated to account for ~68 % of the Universe
