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What is Kepler's First Law?
The orbit of each planet is an ellipse with the sun at one focus
What is Kepler's Second Law?
The radius vector to a planet sweeps out equal areas in equal time
What is Kepler's Third Law?
The square of the period of a planets orbit is proportional to the cube of the semimajor axis of its orbit
What is Newton's First Law?
An object moves at a constant velocity if there is no new force acting on it
What is Newton's Second Law?
Acceleration imparted to a body is proportional to and in the direction of the force applied and inversely proportional to the mass of the body. Force is the cause of a momentum change.
What is Newton's Third Law?
For every force there is an equal and opposite reaction force
What is centripetal force?
A body moving in a circular orbit must have a force towards the centre of its orbit. (speed must be constant but direction is constantly changing).
What is angular momentum?
A body orbiting at radius r with a mass and speed has an angular momentum. Angular momentum of an orbiting body is constant.
What is a semi major axis?
Half of the longest diameter of an elliptical orbit
What is Kepler's Second Law a consequence of?
Conservation of angular motion
What is the Doppler effect?
the relationship between waves, frequency and distance
What are some astronomy applications of the doppler effect?
calculate speed at which stars and galaxies are moving away
help locate new bodies
What is light?
an electromagnetic wave with an oscillating electric wave
What effect does light have on a charged particle?
will exert an oscillating force
What is the result of an oscillating charged particle and electric field?
light emission
What is a blackbody?
a body that absorbs all light
What happens when a blackbody absorbs light?
it gains energy
What is the temperature of a blackbody proportional to?
the kinetic energy of the electrons
In stars what causes an increase in the kinetic energy of the electrons
nuclear fusion
What is W (Wien's constant) equal to?
2.898x10-3mK
What is σ (Stefan-Boltzmann constant) equal to?
5.67x10-8Wm-2k-4
What is the speed of light?
299, 792, 458m/s (3x10^8m/s)
What is K (Coulomb's constant) equal to?
8.99x10^9 Nm^2C^-2
What H line is the Lyman series?
1
What H line is the Balmer series?
2
What H line is the Paschen series?
3
What H line is the Brackett series?
4
What H line is the Pfund series?
5
What is radiative excitation?
Absorbs a photon with energy equal to the energy difference between two levels. The atom will re-emit the photon after a short period.
What is collisional excitation?
Free particles collide with an atom and transfer some of their kinetic energy. The atom returns to its ground state by emitting a photon.
What happens if an atom gains sufficient energy?
An electron may be liberated and the atom becomes ionised
What is Kirchhoff's First Rule?
A hot, opaque solid, liquid or highly compressed gas emits a continuous spectrum
What is Kirchhoff's Second Rule?
A hot, transparent gas emits a spectrum on emission lines. The lines depends on the elements present.
What is Kirchhoff's Third Rule?
If light from a continuous spectrum passes through a lower temperature transparent gas, the cooler gas causes the appearance of absorption lines.
What happens during the birth of a star?
Collapse of a dense, low pressure molecular cloud
How hot does nuclear fusion need to be to form a star?
Above 10million K
When is the main sequence of a low mass star?
50-150 million years
How is H fused into He in a low mass star?
Proton-proton chain
How is the inward gravitational force balanced in a low mass star?
Outward pressure
How does energy reach the surface in a low mass star?
Radiative diffusion and convection
What is convection important for in stars?
Surface activity (solar flares and coronal mass ejections)
What happens to a low mass star after 10 billion years?
Red Giant Phase
Why does a low mass star enter the red giant phase?
Runs out of H in core
What happens when the H shell in a low mass star becomes very hot?
Ignites fusion - the H shell around the inert He burns
At what temperature does He burning begin in a low mass star?
Above 100 million K
How many He nuclei combine to form a C?
3
What supports the core of the star during He burning?
Degeneracy pressure?
What happens when the rate of He fusion rapidly increases?
He flash
At what temperature does C fusion become possible?
600 million K
How does a low mass star eject its outer layers during its death?
Thermal pulses and stellar wind
At what temperature can solid dust particles form in the outflowing wind of a red giant?
1000 - 2000K
What is a white dwarf?
The inert carbon core of a low mass star
What is a planetary nebulae?
When a low mass star ejects its outer layers to form an expanding gas shell. Radiation ionises the gas causing it to glow.
How big are high mass stars?
Above 8 solar masses.
How big are low mass stars?
Less than 2 solar masses
What are the two theories about how high mass stars form?
Same as low mass OR competitive accretion
What is competitive accretion?
Star forms the same as a low mass star
Star continues to accrete gas until depleted
Some stars accrete more efficiently and become high mass stars
How does H fusion occur in high mass stars?
CNO cycle
How many protons form a He in the CNO cycle?
4 (with C catalyst)
When do high mass stars reach the main sequence?
150 000 years
What causes high mass stars to have a higher temperature H core?
Stronger gravity
What do high mass stars become during death?
Super Giants
What does C fusion form?
Heavier elements
What is advanced nuclear burning?
The He nucleus is captured (He capture reaction) to produce heavier elements (C to O).
What happens every time a core depletes the element it is fusing?
Shrinks until hot enough for other fusion reactions
What happens during the final days of a high mass star?
Fe builds up in the Si-burning core
What type of nuclear burning happens in intermediate mass stars?
CNO cycle
Why does an intermediate mass star end up as a white dwarf?
Degeneracy pressure prevents cores becoming hot enough to burn C or O.
Why is iron in the core of a star a problem?
Cannot generate any nuclear energy.
How do elements lighter than Fe gain Energy?
Nuclear fusion
How do elements heavier than Fe gain Energy?
Nuclear fission
What happens to cause the core to collapse in high mass stars?
Gravity pushes electrons past the quantum mechanical limit. Combine with protons to form neutrons and neutrinos are released.
What is formed when the iron core collapses?
Neutron star (a ball of neutrons)
What is a supernova?
The energy released by the collapse of an iron core into a neutron star
What forms if the mass of a neutron star is high enough that gravity overcomes neutron degeneracy pressure?
Black Hole
What prevents further collapse of a neutron star?
Neutron degeneracy pressure
What can be formed in a supernova?
Elements heavier than Fe
Where is most C produced?
Low mass stars
What is the lifetime of a high mass star (10 solar masses)?
10 million years
Why can't Fe fuse?
Lowest mass per nucleon
Where do stars form?
Solar Nebula
What is a solar nebula and how does it form stars?
Cloud of gas and dust that collapses due to its own gravity. Angular momentum causes the cloud to spin faster as it collapses.
In what part of a solar nebula do stars form?
Centre (planets form in the disc)
How do we infer the existence of a formation disc?
Infrared excess
What type of planet forms first?
Gas giants
Why do terrestrial planets form later?
No gas left
What does aerodynamic drag result in in a disc?
Causes solids to collect. If density high enough could form pebbles or planetesimals.
How do grains grow due to streaming instability?
Growing grains settle towards midplane
Grains collect at certain locations
If local solid density is high enough, drag is shut off and the solids can gravitationally collapse to form planetesimals.
What is core growth by pebble accretion?
The gravitational influence of a planetary core and the speed at which a pebble drifts past.
What is escape velocity?
The kinetic energy of the escaping body must be greater than its gravitational potential energy
What is the snow/frost line?
The distance from the star where temperature is less than 170K and H compounds can condense to form ices.
Why are most large planets found past the snow/frost line?
More solid material
What does the final stages of planet formation involve?
oligarchic growth
What is oligarchic growth?
Each body dominates a certain region that grows until it reaches the isolation mass (runs out of planetesimals)
What happens if the embryo mass is larger than the critical mass in a forming planet?
Runaway gas accretion forms a gas giant
After the gas has been depleted, where would you find terrestrial planets forming?
Within the snow/frost line
After the gas has been depleted, where would you find ice giants forming?
Outside snow/frost line
Where would you find short period comets?
The Kuiper Belt
Where would you find long period comets?
the Oort Cloud
Where is the Asteroid Belt?
Between Mars and Jupiter
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