Chapter 12 Flashcards

Question

Hubble found that

Answer 1

the recessional velocity of galaxies against their distance from earth were proportional

Answer 2

v= H0d Where v = recessional velocity in kms^-s d= distance in Mpc ( Mpc = 3x 10^22) H0= Hubbles constant in Kms^-1Mpc

Answer 3

That Hubbles work is strong evidence the universe is expanding

Answer 4

Space itself is expanding and lightwaves are being stretched along with it

Answer 5

The expansion of the universe

Answer 6

V/C = change in λ / λ

Answer 7

13.7 +- Gyr

Answer 8

The universe started iff very hot and very dense and has been expanding ever since

Answer 9

Cosmic Microwave Background radiation: Models of the Big Bang show that, at the beginning of the universe, radiation of a relatively short wavelength would have been produced. Now, this radiation, due to the expansion of space, has been stretched - it has become microwave radiation.

Answer 10

- Corresponds to a temp of 2.73 k - Radiation if largely isotropic and homogeneous - Background radiation shows a doppler shift showing earths motion through space

Answer 11

- Large abundance of helium | - The early universe is very hot and it must've been hot enough for hydrogen fusion to happen and this produces helium

Answer 12

The universe started with the big bang and has been expanding ever since

Answer 13

1.5 x 10^10

Answer 14

3 x 10^8 ms^-1

Answer 15

3 x 10^8 m

Answer 16

approx 10^16 m

Answer 17

-Send out the first radar pules, which then returns once it has collided with the asteroid. -Then do the same after a certain time period. -You can then work out the distance it travelled in between the two pulses using light-seconds You can then use the time take in-between the sets of pulses, and the distance it travelled to work out the relative velocity.

Answer 18

moving away from earth

Answer 19

v = increase in distance / time interval v/c = tback- tout/ tback +tout

Answer 20

- Doppler uses continuous waves instead of pulses - The wavelength of the return signal is changed - If V

Answer 21

Two-way: wavelength changed out and back change in λ/ λ = 2(v/c) One-way: wavelength changed half as much change in λ/ λ = (v/c) -The relative velocity calculated from difference between observed wavelength and source wavelength

Answer 22

An object twice as far away will look a quarter as bright; ten times as far will look a hundred times less bright

Answer 23

M = V^2 r / G

Answer 24

the existence of the cosmic microwave background

Answer 25

- Can we mimicked in a lab with a light box, a lux meter and measuring ruler. - Taking measurements and plotting them reveals the linear relationship between light intensity and the reciprocal of the distance squared. - They are in fact proportional to one another

Answer 26

- We don't know how bright the stars really are | - We assume that light intensity is not affected by different mediums (including the atmosphere)

Answer 27

parallax angle = a + b/ 2 .- This method is only really usable over relatively short distances.

Answer 28

-A parsec, or 1 pc, is a unit of distance. It is defined as the distance between the Sun and an object when the parallax angle is equal to one second of arc -Distance (in pc) = 1/ Parallax Angle (when the angle is measured in seconds of arc)

Answer 29

To determine ∆λ the black lines in the emission spectrum that are absorbed by abundant elements in space (H and He) are tracked, and the movement of the pattern of lines, from what we know to be the true values from experiments on Earth, is used to determine how much the wavelength of the radiation has changed.

Answer 30

H0 = v/r = 1/ time | -This time is the reciprocal of the Hubble constant time 1/ H0 = elapsed since all galaxies in one place.

Answer 31

− This assumes that the speed is constant for a galaxy. Due to gravity it isn’t which gives an over-estimate on the age of the universe. − H0 is not precisely known.

Answer 32

If H0 is low then this implies an old universe (about 20 Gyr). But this data is not what most sources currently obtain. It is increasingly popular to think that H0 is high (say 85) giving a 14 Gyr old universe.

Answer 33

As light travels from one galaxy to another, the universe expands, which stretches the wavelength of the light (or other radiation). This causes a red-shift of the radiation which should not be confused with the red-shift caused by the relative motion of two Distance to galaxy Speed of recession objects (which is known as the Doppler effect).

Answer 34

z = change in λ/ λ corresponds to an expansion in scale of R2/ R1 = 1 + z The fact that everything measured shows a ∆λ > 0 indicates that the distances between every pair of objects is increasing and that the universe is expanding.

Answer 35

A temperature fall is observed because as λ gets longer, f gets lower, so by E = hf, E gets lower, and E ∝ T giving a temperature fall. Today (14 Gyr later) the λ is 1mm (microwaves) and T = 2.7 K. This is also considered to be evidence for the Big Bang.

Answer 36

E= fh where f = frequency of radiation h= planks constant

Answer 37

This is a thought-experiment that suggests that if the Universe is infinite then everywhere you looked in the sky your line of sight would (eventually) end with a star, giving a white sky. Olber found that the sky was black rather than white. He claimed that there were not enough stars for an infinite Universe, so it must be finite.

Answer 38

I ∝ 1/ R*2