Chaptwr 20 Cosmology

Question 1

Astronomical distandes

Answer 1

Because these are so large we use these numbers to help
In order
- light year ( the distance taken for speed of light under one earth year)
- 1 atronomuic, unit which is the average distance from earth to sun
% and the parsec, which is distance at which an angle of 1 ar second sub tends a distance radius of 1 AU

Question 2

As amhles are small what are the atsontnucal measure fo angle

Answer 2

60 arc seconds in an arc minute
60 arc minutes in ONE DEGREE

Therefore 1 arc second si 1/3600 degrees

Question 3

Expressions for arc sending use to being so small

Answer 3

We can find it as tan Ethan = 1 Au / parsec

However a s theta so small theta = 1 Au / pas exec

Keepigj au cosntsnt WD now know angle is inversely protoinsl to the distance in parsecs, with angle in ARCSECODN as theta was in arcsecodn too,

Question 4

Stellar parallax used to find

Answer 4

This is used to find distances if enabry stars , and is used by measuring the apaprent dhjft in dsipaldemmr of a nearby star relative to distant stars, and calculating the parallax angle as a result to find the distance away the Starr from the SUN in oarsecs

Now rememebr measure over opposite or item so 6 months apart, apparent shift in position , use formual

Question 5

Why is it measure robe r6 months

Answer 5

Measured over 6 motnhfs due this the only way both distances are 1 au from each other with proper angle

Then divide angle by 2

Question 6

Why is stellar only used firnstars less than 10lpc away and not further

Answer 6

Because further way, the parallax angle is too small for our current sensitivity equipment to measure, as the shift is not that big when further away comsored Tina much distant. Bskcgrop etc

Question 7

What must the distance and angle be in do MgO lack

Answer 7

MUST BE PARSECS AND ARC SECS

Question 8

Parallax angle defintion

Answer 8

Is the angle that dunstendem a rwofus of 1 au when it’s a certain distance away from the sun in parsecs

Question 9

The Doppler effect

Answer 9

Is the apaprent change in frequency/ wavelength due to the real-time velocity between the oberster and the producer , where’d the change is orotoinwl to the magnetiude of the relwtivevelocoty

Question 10

Explain

Answer 10

As an object moves away from an isverever , the wavelengths which are received by the observer are moving away from Esch other, and thus is edged ti be longer, and so moving away cause and increase in wbakenfgh as they are more spread

However when ti coems towards you, the wvakenfghr csthcu up with Esch other so appears to be sheotter

As a result moving way shifts ti the red soectrum and towards the blue side

Works for sound too

Question 11

In the Finten fi planete

Answer 11

Light coming from planets are red shifted suggesting it is moving away from us , and further away are moving faster

This suggest the expansion if the universe is accelerating
And this is hubbles law, and suggests that if we ere to go back in time, the universe would lesd bsck to a singularity , which explains big bamh

Question 12

Remember , each spectral line is shifted by the same what?

Answer 12

Not the ABSOLUTE SHIFT, but the same PERCENTAGE SHIFT
THEREFORE, as the shift is prodptimsl to Orginal wavkenefht tio, thr higher wvaes geht will SHFIT MORE, then closer

Spcheco if it could be blue or red shift, and then see if red they should be here etc

NOT ABSILTUE , DOMT LACK

Question 13

Why when fast sound chsmges but when I run away fast the colour don’t change

Answer 13

This is because you use the speed , if tisultrasound sue that etc

The speed of something driving away is of same order as speed fo sound, therefor the chnsgein wavkenfht is actually ntocbel the further away it goes

Question 14

Hubbles law

Answer 14

The recessional velocity of GALAXIES are prodptimsl to the distance away from us
- remember nubbles law csn’t be used to desvribe stars in own galaxy because it’s only applicable to GALAXIES

Question 15

Therefor plotting refuses ln velcoty agaisnt distance away of a galaxy, what do we get?

Answer 15

We get a linear relationship as proprtionsl

Therefore the grsdient would be Hubbles CONSTSNT, however ss there is much soresd of velocity, there is high uncertainty in the gradient

Question 16

How is hibbles law evidence for big Bange

Answer 16

It shows that
- galaxies are moving away from us
- and that further galaxies are moving faster away
- therefore the universe expansion is acdwlrwging

This suggests that there must have been a point tracing back in time where the universe was a singularity, and thus backs up the Big Bang

However, it is not CONCRETE PROOF, bevaude other theories also backed expansion of universe, not just big bange

However cmbr, that was all Big Bang ..l

Question 17

What is the cosmological epic up,e

Answer 17

In essence it just means that everything in the universe is ibserved the same

Universe is
- isotpritoc
- this means no edges or centre to the universe, such that it’s observed the same by everyone
- laws of physics apply the same in the whole universe
- uniform density HOMIGENOUS, which means the density of the universe inntersm fo structured is uniform. So galaxies etc are seen everywhere

Gehe crude, as no way ti guan rate physics laws are the same ebeyhwere so predictions made can be off all the time ,

Question 18

Hubbles law breaks down for far away galaxies why?

Answer 18

It is observed that the universe is expanding at an ACCELRWTIGN RATE. Therefore the far away galaxies have acdwlrtwrd too much such that they don’t follow the linear proper inability anymore, and don’t fit the trend. This is what dark energy is for

Close cal shoes can have their motion affected due to Fabriano pulls to our galaxy, and thus they don’t fir hubbles law either ,

Question 19

How does light observed from binary stars shown

Answer 19

DINT SAY BLUE SHIFT A

AS BITH STARS ARE MOVINF AWAY FROM US, THEY WILL SHOW A RED SHIFT
- however as a star orbits closer toward sis, there relative velocity is less than the Starr ibtiting away from us. Therefore it will show a SMALLER RED SHIFT, compared to star orbiting any form us

When observed after a period of time, this will PERIODICALY change its wavelength as red shift ss stars ORBIT

Question 20

Two pieces of evidence euse to support big magne d

Answer 20

Hubbles law, to explain expansion of universe

CMBR to explain Big Bang theory of gamma photons being red shifted with expansion to microwave, with a temelrgsure of 2,7K corresponding

Question 21

What is the big Bange theory?

Answer 21

Is a theory that suggests the creation of the universe
It wa sorigannky a singularity, which was if intiket hot and dense, which has then been expanding to firm the universe we see today, and cooled down with expansion

Question 22

What proves cmbr

Answer 22

Modelling the universe as a black body emitter, using Wiens law the temlertaure of universe should be 2,7k, which it is

Question 23

How to predict the time of the universe and what ASSUMPTION

Answer 23

Assuming that the universe expansion rste was constant ( which is accelerating), then the time taken for expansion would be of the ration D/ V , which is 1/ the grsdient of graph, which is 1 /H0

But this MUST BE in seconds , should be 14 bill

Question 24

Dark energy

Answer 24

Dark energy is energy which is not observed yet but predicted to be the energy which drives the accerlwtion rate of expansion of the universe, not detected yet tho

Question 25

Exolaint he bails for dark matter

Answer 25

When observing mass systems where mos top the mass is concentrated in the evtnree, such as our solar system and orbiting things like the moons of Jupiter, it is seen that the further away from the centre yiu went, the lower the velocity of orbit

However when observing the same thing in stars in bakaxies, this was not seen, it was exoected that the velocity would drop further from the centr,e but instead it stayed pretty CONSTSNT

As a result, since firsts concluded the only for this to be possible was if there was soem sort of matter concentrated at the extremities of the galaxy, which we could not detected, that allows for the speed of the stars to still remain high

This was dark matter

Question 26

Dark matter and it’s priorities

Answer 26

Dark matter is matter that does not interact with normal matter, thus is to ANTIMATTER, and does not emit or absorb photons

Question 27

Letssummarise dark energy and matter

Answer 27

Dark energy si through the tk be the fuel for the accelerating sxpandjon if the universe, permeates all univers and not detcted
Dark matter is though to be matter concentrated in galaxies which allows for the speed of orbit of stars to be just as high as speed of stsrsclose to the centre

When comsored to other mass systems where mass is down in centre like solar system and moons, we thought further awyafkrm centre you go the lower the orbital veloctyl

However not the case when observed with stars in gsksxies was the same, and this is believed to be due to dark matter,

Doesn’t intervst with matter this isn’t antimatter snfdoenst emit or abdirb light,

Question 28

MUST TWKE HRSDIENT OF HUBBLE THROUGH 0,0

Question 29

Fidn the distance e

Answer 29

Pick any set fi baleus and make up your own CONSTSNT snd use thst to fidn fistsnce

Question 30

Fining angle if flach at estranged?

Answer 30

Position galaxy as far as possible, and with bototm of galaxy with middle of earth, this gives you the greatest angle

Remember can’t use Stella parallax that’s fir stars in OWN a galaxy not others

Question 31

How to roofed big. Nahe form data

Answer 31

Show that they back generals edpansion, and away edpanding more, which explains hibbles law snd then explain big Bange form there

Calculate a few times
Find age if universe?

Question 32

To make emission lijes more soresd out , two ways?

Answer 32

1nway is you just want to increase theta. Hold the screen further away , this will increase theta as bith disatnces increase

Or use FINER GRSTIFN A, AS this decreases d , which increases theta as sin increases with value form0 to 90