Cosmology Flashcards
Define the astronomical unit.
The mean distance between the sun and the Earth.
1Au = 1.50x10^11m.
Define lightyear.
The distance that light will travel in a vacuum in one year.
Define 1 Arcminute.
1/60th of a degree. No. of degrees = No. of archminutes/60.
Define 1 Arcsecond.
1/60th of an arcminute, 1/3600th degree. No. of degrees = No. of arcseconds/3600.
Define the parallax angle.
The angle of apparent shift when a relatively close star is viewed from two different positions against background of distance stars.
Define a parsec.
The distance at which 1AU subtends an angle of 1 arc-second. d = 1/p, where d is measured in parsecs and p is the angle in arc-seconds.
Define the term Homogenous.
Matter is distributed uniformly.
Define Isotropic.
A measured value is the same in all directions, for instance an isotropic Universe would look the same in all directions.
Define the Cosmological principle.
When viewed at a large enough scale, the Universe is isotropic, homogenous, and the laws of physics are universal across the universe.
Define the Doppler effect.
Comparative to observation without relative motion, the Doppler Effect is the change in frequency and wavelength due to relative motion between wave source and observer.
Define Blue-shift.
When observed wavelengths appear shorter due to the wave source and observer moving towards each other.
Define Red-shift.
When observed wavelength appear longer due to the wave source and observer moving away from each other.
State Hubble’s law.
The recessional speed of galaxies is approximately proportional to their distance from Earth. v = H0d where H0 is the Hubble constant.
Define Cosmic Background Radiation.
The microwave signal detected at constant intensity in all direction from Earth, with a blackbody profile of 2.7K.
Define the Age of the universe.
t = 1/H0 if we assume that the universe has expanded uniformly since the Big Bang.
