8. Astrophysics

Question 1

where are we

Answer 1

milky way - 100-400b stars

local group - 150-1000 galaxies

laniakea supercluster - 100,000 galaxies

Question 2

what is atmospheric composition

Answer 2

certain discrete missing frequencies from absorbtion spectra

Question 3

red shift

Answer 3

longer wavelength
moving away

Question 4

blue shift

Answer 4

shorter wavelength
moving towards

Question 5

magnitude on shift

Answer 5

speed

Question 6

describe the universe

Answer 6

homogenous
isotropic

Question 7

why are we expanidng

Answer 7

because 99% of celestial objects are moving away from us

Question 8

why was the earth at one point dense and hot

Answer 8

because expanding = cooling, so we have to have been dense and hot at some point

Question 9

evidence for the big bang

Answer 9

expanding
cmbr
elements

Question 10

cmbr

Answer 10

cosmic microwave background radiation

dense hot point = lots of radiation
universe cools = lower wavelength

homogenous radiation = doppler effect = earth is moving through space

Question 11

abundance of elements

Answer 11

more H and He than other elements

early dense and hot is ideal for H and He to form via fusion

Question 12

ptolemy’s model

Answer 12

earth @ centre

good - correct order
good - moon in right spot
good - circular orbits

Question 13

galileo galilei

Answer 13

ur wrong

• shadow periodically across jupiter = moons on jupiter
• mercury sometimes obscured by the sun = wrong order

Question 14

terrestrial planets

Answer 14

rock, metal, minerals

mercury venus earth mars

Question 15

jovian planets

Answer 15

gas giants

jupiter saturn uranus neptune

Question 16

extra bits beyond neptune

Answer 16

oort cloud
kuiper belt

Question 17

planet criteria

Answer 17

1. stable orbit around a star
2. roughly spherical
3. clear orbital region

Question 18

asteroid criteria

Answer 18

1. minor planet
2. terrestrial

Question 19

comet criteria

Answer 19

1. small icy body
2. eccentric elliptical orbit

Question 20

where do asteroids and comets come from

Answer 20

asteroid belts e.g. kuiper, oort

Question 21

satellite criteria

Answer 21

1. orbits a planet

Question 22

centripetal force

Answer 22

any force causing an object to follow a circular path

Question 23

what is the centripetal force if the earth is the central body and the moon is the orbiting body

Answer 23

weight

Question 24

what are the criteria for centripetal force

Answer 24

1. must be accelerating at a constant speed
   (direction changing, magnitude constant)
2. no force of weight in the direction of velocity
   (weight and velocity are perpendicular)
3. no displacement
   (W = Fs = 0)
   (no work done to keep orbit)

Question 25

how to change orbit

Answer 25

do work on the orbit -> changes position within gravitational field of the central body -> changes the orbital radius

Question 26

what is orbital speed dependent on

Answer 26

1. mass of orbiting body 2. gfs of central body / centripetal force 3. orbital radius

Question 27

what is the relationship between orbital speed and orbital radius

Answer 27

higher radius = lower gfs = lower weight = lower speed lower radius = higher gfs = higher weight = higher speed

Question 28

how to measure orbital speed with a little practical

Answer 28

measure radius with a ruler and calculate circumference measure time for multiple rotations with a stopwatch and divide by the amount of rotations for reliability

Question 29

how are stars classified

Answer 29

light from stars contains black lines these lines are frequencies of visible light these frequencies represent the composition of the atmosphere this composition has a lot of hydrogen

Question 30

how is the hydrogen actually found

Answer 30

energy levels are discrete excited electrons (when absorbing discrete energy -> certain frequencies -> certain wavelengths) photons

Question 31

birth of a star

Answer 31

1. stellar nebula 2. gravitational force pulls in material 3. more material more grav force repeat 4. dense core has high temperature and high pressure 5. hydrogen overcomes electrostatic repulsion & fuses 7. protostar

Question 32

how does a protostar go into main sequence

Answer 32

1. the material forms a spherical atmosphere 2. the core keeps on fusing

Question 33

how does a star stay in main sequence

Answer 33

the atmosphere is pulled in by weight the atmosphere is pushed out by fusion pressure

Question 34

death of a star (hydrogen shell burning)

Answer 34

1. core runs out of H 2. core contracts 3. fusion pressure decreases 4. atmosphere pulled in 5. fusion pressure increases 6. fusion pressure > weight 7. expands and cools

Question 35

death of a red giant

Answer 35

1. red giant keeps expanding 2. fusion diminishes 3. heavier elements form (Fe and lower) 4. fusion pressure decreases 5. atmosphere collapses and rebounds from core 6. material thrown out into space (forms a planetary nebula) 7. core gets left behind and keeps fusing (white giant)

Question 36

death of a big star

Answer 36

1. core runs out of H 2. fusion pressure decreases 3. atmosphere collapses 4. elements heavier than Fe are produced 5. force of collapse > electron degeneracy pressure 6. core collapses 7. outer layers rebound from core @ high velocity 8. huge shockwave (supernova)

Question 37

> 1.43MSUN

Answer 37

neutron star aka pulsar - core particles get forced together into densely packed neutrons - 20km diameter - so dense that the only radiation is from the axis of rotation (radio waves)

Question 38

< 1.43MSUN

Answer 38

black hole - core continues collapsing into an infinitely dense point (singularity) - event horizon around black hole - all objects in the EH would need to be > speed of light (300 000 000 m/s) to escape