Chapter 20 - Cosmology Flashcards
define planets
objects with mass sufficient enough for their own gravity, forcing them to take a spherical shape
define dwarf planets
planets where the object has not been cleared by other objects
define planetary satellites
man-made objects which orbit a planet
define asteroids
objects which are too small and spherically uneven to be planets
define comets
small irregularly sized balls of rock, dust and ice
define solar system
a system containing stars and orbiting objects like planets
define galaxies
a collection of stars, dust and gas. has a supermassive black hole at its centre
define nebulae
gigantic clouds of dust and gas
what does a Hertzsprung russel diagram show
the relationship between a stars temperature and its luminosity
what is continuous line spectra
where all visible wavelengths of light are present
what is Stefan’s law
power output is directly proportional to its surface area and temperature ^4
define light year
distance travelled by light in a vacuum in one year. 9.5x10^15m
doppler effect
the change in wavelength and frequency observed as an object moves towards or away from the observer
define parsec
distance from which 1 Astronomical Unit subtends to an angle of one arc second
Hubbles law
velocity of receding objects is directly proportional to their distance from earth
big bang theory
the universe exploded from an extremely hot and dense point, and is still expanding to this day
what is an astronomical unit
the average distance from earth to sun
what can stellar parallax be used to measure
distance between nearby stars
cosmological principle
the universe is isotropic and homogenous, and the laws of physics are universal.
isotropic
universe looks the same from all directions to the observer
homogenous
matter is uniformly distributed across the universe
what is happening if the recessional velocity is negative
the object is moving towards us
how is the temperature of microwave background radiation evidence for the Big Bang
shows universe has cooled over time, whilst still expanding - proving that the universe has expanded from a singular point and is continuing to expand
two characteristics of black holes
infinite density
escape velocity is greater than the speed of light
define luminosity
total radiant power of a star
chandrasekhars limit
maximum mass a white dwarf can have whilst remaining stable. (x1.4 solar masses)
weins law
peak wavelength of emitted radiation is inversely proportional to its absolute temperature
describe the formation of a star
-gravitational attraction pulls together dust and gas to form clouds
-gravitational collapse accelerates as dust and gas gets closer together
-some regions become denser and pull in more gas and dust
- GPE transferred into thermal energy
-result is a hot dense sphere = a protostar
-temperature and pressure must be high enough so that the hydrogen gas nuclei in protostar overcomes the electrostatic repulsion and undergo fusion
- fusion produces helium nuclei - producing a star
Hertzsprung-Russell diagram composition
super giants at top
giants second
dwarfs bottom
main sequence diagonally across (uL - bR)
what is meant by a white dwarf when describing the evolution of a star
core left behind after a red giant has shed its layers
why is our understanding of the very earliest moments of the universe unreliable
state of matter unknown
what is Olber’s paradox
infinite universe
all lines of sight end on stars
night sky should be bright
what does a shorter wavelength mean
a hotter star
what does a greater red shift mean
that galaxies are receding at a greater rate
