8. Astrohphysics

Question 1

What is a universe

Answer 1

Large collection of billions of galaxies

Question 2

What is a galaxy

Answer 2

Large collection of billions of stars

Question 3

What galaxy is our solar system part of

Answer 3

The Milky Way

Question 4

What does gravitational field strength (g) depend on

Answer 4

Mass of the body creating the field

The larger the mass the stronger the gravitational field strength

Question 5

Why is gravitational field strength different on the earth and moon

Answer 5

Earth is more massive than the moon ( large mass)

So an object object would weigh more on earth than it would on the moon

Question 6

Why is gravitational field strength different on different planets

Answer 6

g varies with distance

The closer you get to a star or planet the stronger the gravitational force

Planets closer to the sun orbit it faster because the stronger force requires a larger instantaneous velocity needed to balance it

Question 7

What does gravitational force cause

Answer 7

Orbits

Question 8

What do moons orbit

Answer 8

Planets

Question 9

What do planets orbit

Answer 9

The sun

Question 10

What orbits the earth

Answer 10

Artificial satellites

Eg moons

Question 11

what do comets orbit

Answer 11

the sun ( comets tails face away from the sun)

Question 12

what the differences in the orbits of comets moons and planets

Answer 12

moons and planets= slightly elliptical

comets = highly elliptical

Question 13

Describe a comets orbit

Answer 13

elliptical
longer orbital periods than earth
travel faster when nearer the sun

need to add more

Question 14

equation for orbital speed

Answer 14

(circumference)/ time period

Question 15

how can stars be classified

Answer 15

by colour

Question 16

what are the colors used to classify stars

Answer 16

Blue 
white 
yellow 
orange 
red

Question 17

Describe the relationship between a stars color and it temperature

Answer 17

Blue = Hottest
white 
yellow
orange
red = coolest

Question 18

what is the life cycle of a star with a similar mass to the sun

Answer 18

1. nebula
2. protostar
3. Main sequence star
4. red giant star
5. white dwarf

Question 19

definition of nebula

Answer 19

a cloud of dust and gas

which stars initially form from

Question 20

how is a protostar formed

Answer 20

force of gravity pulls dust and gas together ( to form a protostar)

Question 21

how is a star formed from a protostar

Answer 21

1. gets denser + more particles collide= temp rises
2. temp high enough= hydrogen nuclei undergo nuclear fusion = form helium nuclei
3. nuclear fusion= releases huge amount of energy (thermal expansion)

= keep core of star hot

Question 22

describe a main sequence star

Answer 22

1. long stable period
2. outward pressure caused by thermal expansion ( energy produced by nuclear fusion) balances force of gravity pulling everything inwards )

( the force of gravity holding the star together is balanced by higher pressure due to the high temperatures.)

Question 23

how long does the stable period main sequence star last

Answer 23

several billion years

heavier the star the shorter its time on the main sequence

Question 24

how is red giant formed from a star

Answer 24

1. hydrogen in core used up ( in fusion)
2. force due to gravity = larger than the pressure of thermal expansion
3. star compressed by gravity until dense and hot enough = energy created = outer layers of star expand

( larger nuclei begin to form and the star may expand to become a red giant = bigger than the sun.)

4. star becomes a red giant ( if small star = same size sun)

Question 25

how is a white dwarf formed from a red giant

Answer 25

1. red giant becomes unstable 2. = ejects outer layer of dust and gas 3. = hot , dense solid core = white dwarf

Question 26

describe the evolution of red super giant ( stars much bigger than the sun ) to form a supernova

Answer 26

1. start to glow brightly again 2. undergo more fusion = make heavier elements 3. expand + contract several times as balance shifts between gravity + thermal expansion 4. eventually explode in a supernova

Question 27

how is a neutron star formed from a supernova

Answer 27

1. exploding supernova = throws out layers of dust + gas | 2. = leaves very dense core = neutron star

Question 28

how is a black whole formed form a neutron star

Answer 28

1. if neutron star massive enough = collapse + become black hole 2. black hole = super dense point in space that not even light can escape from

Question 29

PAPER 2 how is the brightness of a star at a standard distance represented

Answer 29

by using absolute magnitude

Question 30

PAPER 2 definition absolute magnitude

Answer 30

measure of how bright a given star would appear to be if it was a fixed distance from Earth = allows us to compare the brightness of stars the lower the absolute magnitude = the brighter the star ( very bright stars = -ve absolute magnitude )

Question 31

PAPER 2 definition of the Hertzsprung-Russell Daigram ( HR diagram)

Answer 31

is a graph of absolute magnitude against temperature for many, many stars

Question 32

PAPER 2 need to be able to draw a HR diagram for the main components

Answer 32

??? Red giant + red supergiant = top right White dwarf = bottom left Main Sequence = span whole range of graph diagonally from top-left to bottom-right

Question 33

PAPER 2 describe the past evolution of the universe + main arguments for the big bang

Answer 33

??? 1. initially all matter of universe occupied a single point 2. this tiny space = very dense + very hot 3. single point the explode = Big Bang 4. space started expanding and the expansion is stil going on

Question 34

PAPER 2 what evidence is there to support the Big Bang

Answer 34

``` Red Shift (suggests universe is expanding ) Cosmic microwave background = CMB ( CMB radiation = leftover energy of this initial explosion ) ```

Question 35

PAPER 2 what happens when a wave source is moving relative to an observer

Answer 35

there will be a change in the observed frequency and wavelength ( compared to when they were emitted ) = Doppler Effect happens with all waves incl. light

Question 36

PAPER 2 definition of red shift

Answer 36

if a light source is moving away from you = light it emits will appear to be shifted towards the red ( ie. lower frequency end ) of the visible part of the EM spectrum

Question 37

PAPER 2 definition of Cosmic Microwave Background ( CMB ) radiation

Answer 37

the low frequency microwave radiation coming from all directions and all parts of the universe ( that scientist can detect )

Question 38

PAPER 2 describe the red shift in light received from galaxies at different distances away from Earth ( why do most galaxies seem to be moving away from each other )

Answer 38

1. different elements absorb different frequencies ( or wavelengths ) of light 2. when light is passed through a sample of an element = pattern of dark lines is produced 3. there is dark line at each of the frequencies in the visible part of the EM spectrum that the element absorbs 4. when we look at light from distant galaxies we see the same patterns but at slightly lower frequencies ( longer wavelengths) than they should be 5. the patterns = shifted towards the red end of the spectrum = red shift

Question 39

PAPER 2 how does red shift of galaxies provide evidence for the expansion of the universe

Answer 39

1. measurements of red shift suggest all distant galaxies are moving away from us very quickly 2. more distant galaxies have greater red shifts than nearer ones = show bigger observed decease in frequency ( increased wavelength ) 3. = more distant galaxies are moving away faster that nearer ones 4. conclusion = whole universe is expanding

Question 40

PAPER 2 what is the equation used for calculations involving red shift i.e. equation to calculate relative speed between 2 galaxies

Answer 40

change in wavelength / ( reference) wavelength = velocity of a galaxy / speed of light

Question 41

PAPER 2 what is the speed if light

Answer 41

3 x 10*8 m/s