Chapter 20 - Cosmology

Question 1

define planets

Answer 1

objects with mass sufficient enough for their own gravity, forcing them to take a spherical shape

Question 2

define dwarf planets

Answer 2

planets where the object has not been cleared by other objects

Question 3

define planetary satellites

Answer 3

man-made objects which orbit a planet

Question 4

define asteroids

Answer 4

objects which are too small and spherically uneven to be planets

Question 5

define comets

Answer 5

small irregularly sized balls of rock, dust and ice

Question 6

define solar system

Answer 6

a system containing stars and orbiting objects like planets

Question 7

define galaxies

Answer 7

a collection of stars, dust and gas. has a supermassive black hole at its centre

Question 8

define nebulae

Answer 8

gigantic clouds of dust and gas

Question 9

what does a Hertzsprung russel diagram show

Answer 9

the relationship between a stars temperature and its luminosity

Question 10

what is continuous line spectra

Answer 10

where all visible wavelengths of light are present

Question 11

what is Stefan’s law

Answer 11

power output is directly proportional to its surface area and temperature ^4

Question 12

define light year

Answer 12

distance travelled by light in a vacuum in one year. 9.5x10^15m

Question 13

doppler effect

Answer 13

the change in wavelength and frequency observed as an object moves towards or away from the observer

Question 14

define parsec

Answer 14

distance from which 1 Astronomical Unit subtends to an angle of one arc second

Question 15

Hubbles law

Answer 15

velocity of receding objects is directly proportional to their distance from earth

Question 16

big bang theory

Answer 16

the universe exploded from an extremely hot and dense point, and is still expanding to this day

Question 17

what is an astronomical unit

Answer 17

the average distance from earth to sun

Question 18

what can stellar parallax be used to measure

Answer 18

distance between nearby stars

Question 19

cosmological principle

Answer 19

the universe is isotropic and homogenous, and the laws of physics are universal.

Question 20

isotropic

Answer 20

universe looks the same from all directions to the observer

Question 21

homogenous

Answer 21

matter is uniformly distributed across the universe

Question 22

what is happening if the recessional velocity is negative

Answer 22

the object is moving towards us

Question 23

how is the temperature of microwave background radiation evidence for the Big Bang

Answer 23

shows universe has cooled over time, whilst still expanding - proving that the universe has expanded from a singular point and is continuing to expand

Question 24

two characteristics of black holes

Answer 24

infinite density
escape velocity is greater than the speed of light

Question 25

define luminosity

Answer 25

total radiant power of a star

Question 26

chandrasekhars limit

Answer 26

maximum mass a white dwarf can have whilst remaining stable. (x1.4 solar masses)

Question 27

weins law

Answer 27

peak wavelength of emitted radiation is inversely proportional to its absolute temperature

Question 28

describe the formation of a star

Answer 28

-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

Question 29

Hertzsprung-Russell diagram composition

Answer 29

super giants at top giants second dwarfs bottom main sequence diagonally across (uL - bR)

Question 30

what is meant by a white dwarf when describing the evolution of a star

Answer 30

core left behind after a red giant has shed its layers

Question 31

why is our understanding of the very earliest moments of the universe unreliable

Answer 31

state of matter unknown

Question 32

what is Olber's paradox

Answer 32

infinite universe all lines of sight end on stars night sky should be bright

Question 33

what does a shorter wavelength mean

Answer 33

a hotter star

Question 34

what does a greater red shift mean

Answer 34

that galaxies are receding at a greater rate