Astronomy Flashcards
Angular momentum
J=mrv
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?
a) km, b) AU, c) light years, d) kpc, e) Mpc, f) Gpc
What is a parsec?
1 parsec - distance at which 1 AU subtends 1’’ (arcsecond)
How do you work out how far away something is if you know its true and apparent sizes?
D = L/(angle)
What are Kepler’s Laws?
- Planets orbit the sun in elliptical orbits with the Sun in one focus
- Line connecting the sun to a planet sweeps at equal areas in equal time
- 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
Combine Newton’s and Kepler’s laws to get Universal Gravitational Theory, and expression relating period and distance from the sun
derive to get F = GMm/r^2
and p^2 = (4pi^2)/(GM)r^3
What is Virial Theaorem, how’s it derived what is used for?
2KE+PE = 0 applies to any gravitational system in equillibrium.
It is used to determine whether orbit is bound or not.
Describe how astronomers measure distance using Parallax.
D = 1AU/theta or D(pc)= 1/theta(arcsec)
How does units of magnitude work?
The smaller the value the brighter the star
Flux
F = L/4pi r^2, Js^(-1)m^(-2)
How do astronomers measure distance using apparent and absolute magnitude?
M = m -5log10(D/10pc)
m - apparent, M - absolute
Wein’s law
lambda_max = 2.9*10^(-3)/T(K)
wavelength that is radiated the most
color magnitude diagram, relation of temperature and color/wavelength, luminosity and apparent magnitude
https://en.wikipedia.org/wiki/Hertzsprung–Russell_diagram
What is fusion?
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
Outline the process of nuclear fusion.
see notes
What are the main ways by which energy is transported within a star?
radiation, convection, conduction(less important)
List the possible end points of stellar evolution
mass is less than 8 suns - white dwarf, mass is greater than 8 suns - black hole or neutron star
Ideal Equation of State
p = p(ro)kT/m
Explain what is meant by a supercritical chain reaction
more than one neutron goes on to trigger further fission -> reaction rate increases exponentially
When is nuclei stable?
At low mass numbers N~Z, at high - N>Z, N - neutrons, Z - protons
What are delayed and prompt neutrons?
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 .
Explain why delayed neutrons are useful for controlling nuclear reactors.
They notably slow gown exponential growth of reaction. (maths)
What types of objects could produce gravitational waves?
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
. How do gravitational wave detectors work?
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
What evidence do we have for previous large-scale impacts?
the enhanced iridium content of the narrow KT-boundary layer
What are the possible types of equilibrium of the Earth?
interglacial, ice age,
Physical meaning of luminosity
????Luminosity - how much energy is emitted per second, flux - how much energy is emitted per second per metre squared at certain distance, intensity -
. What is the albedo of an object?
Fraction of incoming radiation that gets reflected
