20

Question 1

Define light year

Answer 1

The distance travelled by light in a vacuum in one year.

Question 2

Define the AU

Answer 2

Astronomical unit . The average (cos elliptical) distance from Earth to sun.

Question 3

Define a parsec (pc)

Answer 3

The distance at which a radius of 1AU subtends an angle of 1 arcsecond

Question 4

What is stellar parallax?

Answer 4

The apparent shift in the position of an object relative to a background of distant objects

Question 5

Why is it not accurate to Measure distances above 100pc

Answer 5

Angießen are so small they are not accurate to measure

Question 6

What is the formula for using parallax to calculate distance ?

Answer 6

Question 7

What is the cosmological principle?

Answer 7

Universe is isotopic and homogeneous and the law of physics are universal. Isotropic means same in all directions to every observer, no centre/edge. Homogeneous means that matter is uniformly distributed- density is the same throughout

Question 8

What is the Doppler Effect?

Answer 8

The apparent shift in wavelength occurring when the source of waves is moving

Question 9

What is the Doppler equation?

Answer 9

Question 10

What is Hubbles law?

Answer 10

The recessional velocity v of a galaxy is proportional to its distance from Earth. The further away a star is from Earth, the a faster it is moving from us

Question 11

How does Hubbles law provide evidence that the universe is expanding?

Answer 11

Most light from distant galaxies is red shifted, showing that galaxies are moving away from Earth, this suggested that space and time is expanding

Question 12

What is the big bag theory?

Answer 12

All objects were initially contained in singularity, which suddenly expanded outwards

Question 13

What are the two pieces of evidence for big bang theory?

Answer 13

CMBR (cosmic microwave background radiation): gamma wavelength expanded to now be in microwave region
Hubbles law : red shift of distant galaxies

Question 14

What explains why acceleration of universe “outwards” has sped up recently?

Answer 14

Acceleration needs a source of energy, aka dark energy which hasn’t been detected (68% of universe)

Question 15

Explain reasoning behind this

Answer 15

Predicted to be decreasing as distance from centre of galaxy increases and so velocity decreases.

Explanation: mass of galaxy not concentrated in the centre

Question 16

Light from a distant galaxy is red shifted. Suggest how by measuring the red shift of different parts of the galaxy , astronomers can determine the speed of rotation of the galaxy

Answer 16

Each side of rotating galaxy will have a different relative velocity and so a different red shift. The side rotating away from us will have a greater velocity (and so greater red shift) than the side rotating towards us.. using Doppler equations the relative velocity of each side can be calculated. The differences in these relative velocities can be used to determine the speed of rotation

Question 17

What was the nature of universe (10^-34)?

Answer 17

Temp= 10^28
Only EM radiation existed (gamma)
Acceleration (inflation)

Question 18

What was nature of universe (10^-6)?

Answer 18

First particles gain mass

Question 19

What was the nature of universe (1s)

Answer 19

Creation of matter stops after about 1s once temperature has dropped to 10^9K

Question 20

what are some charactertistics of black holes?

Answer 20

• escape velocity > c
• absorbs all light/ doesnt emit
• infinte

Question 21

why do measurements deviate of nearby galaxies deviate for hubbles constant?

Answer 21

strong gravitational force between nearby galaxies affects motion

Question 22

why do measurements deviate of far away galaxies deviate for hubbles constant?

Answer 22

expansion rate may not be linear coz of dark matter distribution