8) Astrophysics Flashcards
Units: mass, distance, velocity, acceleration, force, time, gravitational field strength
-Mass: kilogram (kg)
-distance: metre (m)
-velocity: metre per second (m/s)
-acceleration: metre per second squared (m/s2)
-Force: newton (N)
-time: second (s)
-gravitational field strength: newton/kilogram (N/kg)
The universe
Large collection of billions of galaxies
A galaxy
Large collection of billions of stars
Why does gravitational field strength vary
-the greater the mass of the planet, the greater its gravitational field strength, larger attractive force towards the centre of the planet or moon
Gravitational field strength on earth vs other planets
Earth: approximately 10 N/kg
Moon: less than earth - easier to lift a mass on the surface of the moon than on Earth
Gravitational force
Provides a force that is pulling smaller bodies towards a star or planet
-gravitational force exerted by the larger body on the orbiting object is always attractive
-force always acts towards the centre of the larger body
-causes the body to move and maintain a circular path
Different astronomical orbits - planets, moons, comets, artificial satellites
-planets orbit the Sun
-moons orbit planets
-comets orbit the Sun
-artificial satellites orbit the Earth or any body in the Solar System
Similarities in the way different planets orbit the Sun
-orbits are all slightly elliptical with the Sun at approximately the centre of the orbit
-all orbit in the same plane
-all travel in the same direction around the Sun
Differences in the way different planets orbit the Sun
-different orbital radius
-different speeds
-different orbital periods
Orbits of moons
-Moons orbit planets in a circular path
-Some planets have more than one moon
The closer the moon is to the planet:
-The shorter the time it will take to orbit
-The greater the speed of the orbit
Orbits of comets
Orbits are highly elliptical (very stretched) or hyperbolic
-Not all comets orbit in the same plane/ direction as the planets
-As the comet approaches the sun, its speed increases - in order to maintain a stable orbit or it will be sucked into the object it is orbiting
-As it moves further away from the sun, its speed decreases
Calculating orbital speed
The time taken for an object to complete one orbit
velocity (m/s) = 2π radius (m)/ orbital period (s)
v= (2πr)/T
Classification of stars
-warm objects emit infrared light
-extremely hot objects emit visible light
-colour they emit depends on how hot they are related to their surface
-astronomical objects cool as they expand, heat up as they contract
blue (hottest) –> white –> yellow –> red (coolest)
Life cycle of stars similar mass to the sun
- Nebula
- Protostar
- Main sequence star
- Red giant
- White dwarf
Life cycle of stars similar mass to the sun - nebula
All stars form from a giant cloud of hydrogen gas and dust called a nebula
Life cycle of stars similar mass to the sun - protostar
The force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas - Protostar
-density increases
-more frequent collisions
-temperature increases
Life cycle of stars similar mass to the sun - main sequence star
-Protostar becomes hot enough, nuclear fusion occurs within its core- hydrogen to helium
-thermal expansion due to fusion occur
-force of gravity keeps star in equilibrium
-inward force of gravity = outward pressure force from the expanding hot gases
Life cycle of stars similar mass to the sun - red giant
-After several billion years - hydrogen causing the fusion reactions start to run out
-core shrinks and heats up as the inward force due to gravity > outward force as pressure decreases
-A new series of reactions occur (helium to beryllium)
-As the core shrinks, reactions cause outer part to expand
-Becomes a red giant -red as the outer surface starts to cool
Life cycle of stars similar mass to the sun - white dwarf
-The star will eventually become unstable
-The core which is left behind will collapse completely, due gravity, becomes white dwarf
-cools, amount of energy emitted decreases
Life cycle of large stars
- Nebula
- Protostar
- Main sequence star
- Red super giant
- Supernova
- neutron star/ black hole
Life cycle of large stars - red super giant
-After several billion years - hydrogen causing the fusion reactions start to run out
-core shrinks and heats up as the inward force due to gravity > outward force as pressure decreases
-A new series of reactions occur (helium to beryllium)
-As the core shrinks, reactions cause outer part to expand, becomes red super giant
Life cycle of larger stars - supernova
-fusion reactions finish
-the core of the star will collapse causing a gigantic explosion - supernova
Life cycle of larger stars - neutron star
-At the centre of this explosion (supernova) a dense body - neutron star - will form
Life cycle of larger stars - black hole
-In the case of the largest stars, the neutron star will continue to collapse under the force of gravity until it forms a black hole
-A black hole is an extremely dense point in space that not even light can escape from
Absolute magnitude
Astronomers use this to measure the brightness of stars at a standard distance (if they were all the same distance from earth)
-scale runs back to front: brighter, smaller magnitude
Brightness of a star
-the amount of light the star emits
-how far away the star is
Hertzsprung-russel diagram
-increasing luminosity compared to the sun (y-axis)
-decreasing temperature (x-axis)
-most stars lie on the main sequence
-white dwarfs dimmer and hotter than red giants
-red giants are brighter and cooler than white dwarfs
-draw it
The Big Bang theory
-14 billion years ago, the Universe began from a very small region that was extremely hot and dense
-there was a giant explosion - big bang
-caused the universe to expand from a single point, cooling as it does so, to form the universe today
-universe continues to expand
Absorption spectra
-longer wavelength - red
-shorter wavelength - purple
All wavelengths of visible light are emitted from the sun towards earth
-sun’s atmosphere contains lots of different chemicals and some of them can absorb certain wavelengths of light
-when light reaches earth, certain wavelengths are missing, absorption spectra ends up with a pattern of dark lines
Galactic red shift
-when we analyze light from distant galaxies, their absorption spectras have the same pattern as for the sun but shifted towards red end - red shift
-distant galaxies emitting light are moving away from earth so as waves are travelling towards us, they are stretched
Doppler effect
The apparent change in the frequency/ wavelength of a wave due to the relative motion of the source and observer
-coming towards you, wavelengths are shorter, galaxy moving towards, blue shift
-going away from you, wavelengths are stretched, galaxy moving away, red shift
How does doppler effect prove big bang theory
-space between us and galaxy are expanding
-all galaxies are moving away from earth and each other
Expected after an explosion
-some matter is light, greater speed, further from source of explosion
-some matter is heavier, slower speed, closer to source
Cosmic Microwave Background Radiation (CMBR)
-observe that distant galaxies are receding away, so universe is expanding so single point in the beginning
-where there would be very high energy gamma waves
-as universe expanded, the high energy gamma waves with short wavelengths would be stretched
-to x-rays, UV rays, visible light, infrared, and finally microwaves
-which we now observe from all directions in the universe
