Chaptwr 20 Cosmology Flashcards
Astronomical distandes
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
As amhles are small what are the atsontnucal measure fo angle
60 arc seconds in an arc minute
60 arc minutes in ONE DEGREE
Therefore 1 arc second si 1/3600 degrees
Expressions for arc sending use to being so small
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,
Stellar parallax used to find
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
Why is it measure robe r6 months
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
Why is stellar only used firnstars less than 10lpc away and not further
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
What must the distance and angle be in do MgO lack
MUST BE PARSECS AND ARC SECS
Parallax angle defintion
Is the angle that dunstendem a rwofus of 1 au when it’s a certain distance away from the sun in parsecs
The Doppler effect
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
Explain
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
In the Finten fi planete
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
Remember , each spectral line is shifted by the same what?
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
Why when fast sound chsmges but when I run away fast the colour don’t change
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
Hubbles law
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
Therefor plotting refuses ln velcoty agaisnt distance away of a galaxy, what do we get?
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
How is hibbles law evidence for big Bange
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
What is the cosmological epic up,e
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 ,
Hubbles law breaks down for far away galaxies why?
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 ,
How does light observed from binary stars shown
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
Two pieces of evidence euse to support big magne d
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
What is the big Bange theory?
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
What proves cmbr
Modelling the universe as a black body emitter, using Wiens law the temlertaure of universe should be 2,7k, which it is
How to predict the time of the universe and what ASSUMPTION
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
Dark energy
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
