Astrophysics EP

Question 1

Explain the problem of using the transit method to detect a small planet

Answer 1

(k) transit measures how much light is blocked by a planet
The planet is small so little light is blocked

Question 2

What is meant by Rayleigh criterion

Answer 2

The minimum subtended angle between two objects who image can be resolved

the central maximum of one object coincides the first minimumof the other

Question 3

What is meant by standard candles

Answer 3

Objects whose absolute magnitude is known

Question 4

What formula do you use to find temperature using a graph of wavelength

Answer 4

Wiens

Question 5

What is the absolute magnitude of type 1a supernova

Answer 5

-19.3

Question 6

How do you draw a type 1a supernova graph

Answer 6

Absolute magnitude -20 to -12
X axis from 0 to 400 days in 100 days interval, peak at 0

Question 7

How does the measure of supernovae type 1a lead to a controversy concerning the behaviour of the universe

Answer 7

Measurements of the supernova does no agree with Hubble’s law

So the universe must be expanding at an increasing rate

Must be due to dark energy

Question 8

Why does B class stars have prominent Hydrogen Balmer absorption lines?

Answer 8

B class stars are hot enough to have hydrogen in n=2 state

Question 9

Describe the main features of the radial velocity method in detection of planets

Answer 9

There is a periodic doppler shift in light from the stars

Due to the star and planet orbiting a common centre of mass

Question 10

Why is a nearby red giant dangerous for life on earth

Answer 10

As the star may collapse and become a supernova, which produces gamma ray burst

The gamma would kill our cells

Question 11

Why would supernovas not be in HR diagram

Answer 11

Absolute magnitude is around 20

temperature would be too high

Question 12

Why would black holes not be in the HR diagram

Answer 12

Black holes escape velocity is greater than speed of light so no light is emitted

black holes are too cold to be put in the scale

Question 13

What is meant by cosmological microwave background radiation?

Answer 13

Radiation from all over the universe

When the universe has cooled sufficiently to decouple matter and radiation

Radiation has been red shifted to microwaves as the universe expands

Question 14

Explain how the abundance of hydrogen supports the big bang theory?

Answer 14

Suggests fusion occurred between hydrogen to form helium during the big bang

However as the universe began to cool down and expand, fusion stopped

as a result there is a relative abundance of hydrogen and helium

Question 15

What causes a variation in wavelength

Answer 15

The doppler effect

Question 16

What star is small but hot

Answer 16

White Dwarf star

Question 17

What star is big but cool

Answer 17

red giants

Question 18

Why do we use hydrogen balmer for the analysis of wavelengths on class A stars

Answer 18

As Hydrogen balmer lines are strongest for class A stars meaning they’re more easily measured.

Question 19

Explain how an orbiting planet causes a doppler shift in the spectrum of a star

Answer 19

Planets and stars orbit around a common centre of mass that means it moves away from earth as it orbits

As a result wavelengths of light received from stars shift.

Question 20

define absolute magntude

Answer 20

It is the apparent magnitude from 10pc away

Question 21

same spectral class indicates what two things in common?

Answer 21

temperature
colour (spectral lines)

Question 22

define a black hole

Answer 22

When escape velocity is higher than speed of light

Question 23

how to work out the age of the universe

Answer 23

1/H * MPC / 10^3 = time

Question 24

What is red shift

Answer 24

The increase in wavelength due to recessional velocity between the source and observer

Question 25

Explain why type 1a supernovae can be used as standard candles to determine distances

Answer 25

As apparent magnitude can be measure

The peak absolute magnitude is the same

Question 26

Why is it important for astronomers to have several independent methods of determining the distance to galaxies

Answer 26

To make accepted value for distances for reliable

Question 27

3 marks, how existence of cosmological microwaves explain prove the big bang

Answer 27

Radiation like gamma rays come from all around the universe

as the universe cooled and expanded, matter and radiation decoupled

due to red shift, as the universe was expanded the cosmological gamma rays expanded to microwaves

Question 28

3 marks, explain for the existence of abundance of hydrogen and helium explain occurrence of the big bang

Answer 28

Brief period of fusion of created the abundance of hydrogen and helium

as the universe expanded and cooled the fusion stopped

3:1 ratio of hydrogen and helium in the universe

Question 29

What to look at when confirming if a pair of stars are in a binary system or not

Answer 29

• compare the colour via the spectral class due to temperature
• Ratio of brightness, how many times brighter
• comparing power output
  pc = o a T^4

same distance meaning binary system

Question 30

What to compare between reflecting telescope and radio telescope

Answer 30

• resolving power (minimum angular resolution)
• collecting power
• position
• structure

Question 31

Compare the position and structure of reflecting telescope and radio telescope (similarities and differences)

Answer 31

Positioning
Both can be ground based
- reflecting needs to be at higher altitudes due to absorption of atmosphere, water vapour, ozone layer and pollution
- radio telescope needs to be in quiet places but can be on the ground

Structure; both use parabolic mirror or dish
- reflecting has secondary mirror
- radio can be made out of wired mesh

Question 32

describe main features of radial velocity method of detecting exoplanets

Answer 32

Measure periodic doppler shifts in light received from the star
Star and planet orbiting a common centre of mass

Question 33

Measuring of distant quasars, what is one problem

Answer 33

Due to dark energy, universe is constantly accelerating when expanding

Uses hubbles law or inverse square law is unreliable over large distances

Question 34

describe radial velocity/doppler effect

Answer 34

• both orbit a common centre of mass
• exoplanet orbits a star, only a star emits light
• star wobbles causing a variation in red shift

Question 35

describe transit method

Answer 35

exoplanet that does not emit light periodically cover the star
- size of dip in light shows size of star
- time period show orbiting period

Question 36

why may a quasar no longer emit radiation

Answer 36

quasars are formed around black holes

black holes no longer have radiation falling into them

Question 37

Why