Module 5 Part 2- Astrophysics Flashcards
What is a gravitational field
A gravitational field is an area of attraction created by a mass which attracts other masses-every mass has a gravitational field but it is usually negligible unless it is a massive object like the earth
What is gravitational field strength-g
Gravitational field strength is the force experienced per unit mass. It is also a vector quantity which acts towards the centre of mass and is indirectly proportional to the distance from the centre
Gravitational field lines around a mass are:
Radial
What does it mean that the force lines on a mass are radial
The lines get further from each other the further away from the mass which shows how the field decreases in strength
What is G and what is the value of it (in formula book)
G is the universal gravitational constant and it has a value of 6.67x10^-11
What is newtons law of gravitation and what is the equation
The force between two masses is directly proportional to the product of their masses and indirectly proportional to the distance between them squared
F=-GMm/r^2
What is the equation for gravitational force
F=(-GMm)/r^2
What is a uniform gravitational field and give an example
A gravitational field where the value of g is the same everywhere for example on the surface of earth
What is keplers first law
A planets orbit is elliptical with the object it is orbiting as one of the foci
What is keplers second law
A line segment joining the planet to the sun sweeps out equal areas during equal intervals in time
What is keplers third law and what is the equation for it
The square of the orbital period of a planet is proportional to the average distance between the masses cubed
T^2=(4π^2/GM) r^3
What is the equation for the speed of a planet and how do you arrive there
v= √(GM/r), this equation is arranged when you consider the orbit as a circle and use the circular motion equation for centripetal force and set it equal to the gravitational force equation
What is a satellite
A satellite is any object which orbits around another object usually of much larger mass (earth is a satellite to the sun)
What are the types of orbit for satellites (earth satellites)
Polar orbit, equatorial orbit, low earth orbit and geostationary orbit
What is a geostationary orbit
An orbit which has a period of 24 hours, satellites in this orbit spin around the earth at the same rate the earth spins and therefore stay in the same place in the sky
What is gravitational potential
Gravitational potential is defined as the work done per unit mass to move that object to that point from ‘infinity’ which essentially means from a point where g is zero
What is the equation for gravitational potential
V=(-GM)/r
What does perihelion and aphelion mean
Part of orbit which is closer to star-perihelion
Part of orbit which is further from star-aphelion
What are the three assumptions of cosmological principle
The universe is homogeneous-equal density
The universe is isotropic-same in all directions
The universe has the same laws of physics everywhere
What is an AU
AU=astronomical unit which is the distance from the earth to the sun
What is a ly
ly=light year which is the distance light travels in one year
What is an arc minute and arc second
An arc minute is 1/60 of a 1 degree angle
An arc second is 1/60 of an arc minute
Therefore an arcsecond is 1/3600 of a degree
What is a pc
pc=parsec
A parsec is the distance that, when combined with one astronomical unit in a 90 degree triangle, creates an angle of 1 arcsecond
What is parralax
Parallax is the apparent change in an objects position due to a change in the viewing position
What is stellar parallax and how does it work
Stellar parallax is a technique which utilises the effect of parallax to measure the distance of stars less than 100 pc away.
It works by recording the position of a star relative to the ‘fixed’ position of other stars very far away at different points in the year.
This data is then used to calculate the parallax angle in arcseconds
What is the equation that links distance (in parsecs) and parallax angle
d=1/p when p is in arc seconds (hence the terms par-secs)
What is gravitational potential
Gravitational potential energy per unit mass (similar to potential difference)
What is the relationship between g and r inside and outside a planet
Inside: g∝r
Outside: g∝1/r^2
Gravitational potential is the amount of energy needed to move an object of one kilogram from a point of
infinity
What is escape velocity
Escape velocity is the velocity needed to escape a gravitational field
What is the equation for escape velocity and how do you arrive there (show working)
V=(2GM/r)^1/2
Set the equation for kinetic energy equal to the equation for gravitational potential energy and re arrange
What are the stages of a stars life cycle and briefly explain them
Nebulae-cloud of dust and gas
Protostar-hot ball of dust and gas due to friction
Main sequence-hot and dense enough ball to begin nuclear fusion
Red giant-hydrogen fuel runs out and star expands due to heavier elements being used
White dwarf-all fuel runs out and star contracts to become a small dense mass
What is the Chandrasekhar limit and explain
The threshold mass for a star to be able to overcome the electron degeneracy pressure and fuse elements up to iron, causing a red super giant
Given the quantity 1.44M where M is the mass of the sun
What happens to a star if it becomes a red super giant
The red super giant will use its fuel until it runs out and causes a supernova
If the star is between 1.44M-2M it will become a neutron star
If the star is above 2M it will overcome the neutron degeneracy pressure and become a black hole
What are the three types of light unit
Luminous emittance-Lux
Luminous flux-Lumen
Luminous intensity-Candela
What is the brightness of a star dependent on (when viewed from earth)
The luminosity and the distance
What is the Hertzsprung-Russel diagram
A graph that plots the luminosity against the temperature of a star
What are the seven categories on the Hertzsprung Russel diagram and what do they equate to
O-He plus, He, H
B-He, H
A-H, ionised metals
F-ionised metals
G-metals
K-neutral metals
M-neutral atoms
What would be found in the top left of the Hertzsprung Russel diagram
Blue giants
What would be found in the top right of the Hertzsprung Russel diagram
Red super giant
What would be found in the bottom left of the Hertzsprung Russel diagram
White dwarf
What would be found in the mid right of the Hertzsprung Russel diagram
Red giant
When an electron moves to a higher energy level it is
Excited
When an electron moves to a lower energy level it is
Relaxed
What is a black body
An idealised body that does not reflect of transmit, it only absorbs it and hence is called black.
Therefore light of any wavelength that is shone on a black body will disappear inside the black body and it’s energy will be absorbed.
What happens when a black body is heated above absolute zero
This causes the electrons (and protons) to oscillate in the EM field which causes light to be emitted-aka black body radiation
What is wiens law + equation
The hotter a black body is the shorter the maximum wavelength
What is Stefans law + equation (attack on titan)
The larger the surface area of the star, the larger luminosity (power) it emits
L=A x σ x T^4
(where σ is the Stefan constant)
What is the Doppler effect
The apparent change in a wave’s frequency due to relative motion between the source of the wave and the observer
What is the name for the Doppler effect for light which provides evidence for the Big Bang
Red shift
What is hubbles law + equation
The further a galaxy is away, the greater the red shift will be
V=Ho x d
What are two pieces of evidence for the big bang
Red shift
Cosmic microwave background radiation
