Astronomy

Question 1

Angular momentum

Answer 1

J=mrv

Question 2

What are the physical scales associated with (a) the circumference of the Earth; (b) the
distance from the Earth to the Sun; (c) the distance to the nearest stars; (d) the size of the Milky Way; (e) the distances between galaxies; (f) the size of the observable Universe?

Answer 2

a) km, b) AU, c) light years, d) kpc, e) Mpc, f) Gpc

Question 3

What is a parsec?

Answer 3

1 parsec - distance at which 1 AU subtends 1’’ (arcsecond)

Question 4

How do you work out how far away something is if you know its true and apparent sizes?

Answer 4

D = L/(angle)

Question 5

What are Kepler’s Laws?

Answer 5

1. Planets orbit the sun in elliptical orbits with the Sun in one focus
2. Line connecting the sun to a planet sweeps at equal areas in equal time
3. Square of orbiting period is directly proportional to the cube of average distance from the sun
   p^2 = ka^3
   Special case for solar system
   p(years)^2 = a(AU)^3

Question 6

Combine Newton’s and Kepler’s laws to get Universal Gravitational Theory, and expression relating period and distance from the sun

Answer 6

derive to get F = GMm/r^2

and p^2 = (4pi^2)/(GM)r^3

Question 7

What is Virial Theaorem, how’s it derived what is used for?

Answer 7

2KE+PE = 0 applies to any gravitational system in equillibrium.
It is used to determine whether orbit is bound or not.

Question 8

Describe how astronomers measure distance using Parallax.

Answer 8

D = 1AU/theta
or D(pc)= 1/theta(arcsec)

Question 9

How does units of magnitude work?

Answer 9

The smaller the value the brighter the star

Question 10

Flux

Answer 10

F = L/4pi r^2, Js^(-1)m^(-2)

Question 11

How do astronomers measure distance using apparent and absolute magnitude?

Answer 11

M = m -5log10(D/10pc)

m - apparent, M - absolute

Question 12

Wein’s law

Answer 12

lambda_max = 2.9*10^(-3)/T(K)

wavelength that is radiated the most

Question 13

color magnitude diagram, relation of temperature and color/wavelength, luminosity and apparent magnitude

Answer 13

https://en.wikipedia.org/wiki/Hertzsprung–Russell_diagram

Question 14

What is fusion?

Answer 14

nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles

Question 15

Outline the process of nuclear fusion.

Answer 15

see notes

Question 16

What are the main ways by which energy is transported within a star?

Answer 16

radiation, convection, conduction(less important)

Question 17

List the possible end points of stellar evolution

Answer 17

mass is less than 8 suns - white dwarf, mass is greater than 8 suns - black hole or neutron star

Question 18

Ideal Equation of State

Answer 18

p = p(ro)kT/m

Question 19

Explain what is meant by a supercritical chain reaction

Answer 19

more than one neutron goes on to trigger further fission -> reaction rate increases exponentially

Question 20

When is nuclei stable?

Answer 20

At low mass numbers N~Z, at high - N>Z, N - neutrons, Z - protons

Question 21

What are delayed and prompt neutrons?

Answer 21

Delayed neutrons are released from the decay of fission products.
Prompt neutrons are released directly from fission within 10 seconds of the fission event. Average energy 2MeV .

Question 22

Explain why delayed neutrons are useful for controlling nuclear reactors.

Answer 22

They notably slow gown exponential growth of reaction. (maths)

Question 23

What types of objects could produce gravitational waves?

Answer 23

primordial gravitational wave/quantum fluctuations, merges of the supper massive black holes in the centre of the galaxy, mergers of compact object binaries (black holes, neutron stars), asymmetric supernova explosions, neutron stars with crustal asymmetries

Question 24

. How do gravitational wave detectors work?

Answer 24

LIGO: Two arms of length 4km sit at right
angles, each containing an ultra high vacuum. Lasers measure the relative length of the arms by constructive and destructive interference by the recombining light waves. Sensitive to the deformations due to GW

Question 25

What evidence do we have for previous large-scale impacts?

Answer 25

the enhanced iridium content of the narrow KT-boundary layer

Question 26

What are the possible types of equilibrium of the Earth?

Answer 26

interglacial, ice age,

Question 27

Physical meaning of luminosity

Answer 27

????Luminosity - how much energy is emitted per second, flux - how much energy is emitted per second per metre squared at certain distance, intensity -

Question 28

. What is the albedo of an object?

Answer 28

Fraction of incoming radiation that gets reflected