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what do all stars begin as
nebula (a cloud of dust and gas)
what are nebulae pulled together by to form
pulled together by gravity to form a protostar
what does the gravitiational attraction cause to increase and what does this cause
causes the density of a protostar to increase, causing more collisions between particles to occur, causing temp to rise enough for nuclear fusion to occur.
what fuses in main sequence stars to form heluim
hydrogen
why are main sequence stars stable
equilibrium between the force of gravity acting inwards on the star then the forces pushing outwards caused by the energy released by nuclear fusion
what happens to main sequence stars as they begin to run out of hydrogen
as there’s no more fusion occurring the star begins to collapse in on itself as energy released by fusion balances the inward pull of gravity
the core begins to contract as it does so, it releases thermal energy,a s the gravitational energy is converted into thermal energy
however even though the core has run out of hydrogen the outer layers haven’t and so they comtinue fusion, fusion begins in a shell around the core, where the remaining hydrogen fuses into helium
The energy produced by shell fusion causes the outer layers of the star to expand. As the star grows in size, it cools down and becomes a red giant.
what is the fusion in stars responsible for
producing all naturally occurring elements up to iron
what does the life cycle of a star after the main sequence depend on
mass
what happens to stars that are the same size as the sun after the main sequence
they become red giants
what happens to red giants once they eventually eject their outer layer
they become white dwarfs which cool to become black dwarfs
what happens to stars bigger than the sun
they turn into red super giants
what happens when red super giants explode in supernova
they form heavier elements than iron ejecting them into the universe
what do supernova stars leave behind
either a neutron star or for stars with a high enough mass a black hole
what has produced all naturally occurring elements and distributed them through out the universe
fusion in stars and supenovae
what is an orbit
the path on which one object moves around another
what do planets and dwarf planets orbit
stars
example of a natural satlelite
the moon
where is our solar system located
in the milky way
what shape are orbits
circular
why do objects travel in orbit
due to the force of gravity between two objects
what direction does gravity act in an orbit and what does this cause
acts towards the centre of the orbit, causing an acceleration which changes the velocity but not the speed of the orbiting object
when is the gravitational force the strongest
the closer you are to the object
what does a faster orbital speed mean
a smaller orbital radius for the object to be in a stable orbit
what is the effect known as red shift
The increase of wavelength of light from a distant Galaxy moving away from the earth
what does red shift do
all galaxies are moving away from us
what is the relationship between the speed of distant and nearer galaxies
distant galaxies are moving away faster
what does galaxies moving away from us suggest
the universe is expanding all galaxies are moving away from each other
what do the observations of red shift and cosmic microwave radiation support
the big bang theory
what does the big bang theory state
that the universe was once confined to a very small area that was very hot and dense which exploded and has been expanding ever since
What is centripetal acceleration?
at any instant the object is moving at a tangent to the circular path, the unbalanced centripetal force acting on the object causes an acceleration as it's still changing direction (velocity)
which direction does acceleration act in?
the centre of the circle
which are the most likley forces to act as a centripetal force?
gravity. tension, frcition and reaction
What did Edwin Hubble discover?
found that all far away objects such as galaxies are moving away from us and that this motion called their recession velocity is greater the further they are away from us
what happens to wavelength when frequency increases?
it decreases and vice versa
what is geostationary orbit?
This is a specific type of orbit in which the satellite:
- Remains directly above the equator
- Always orbits at the same point above the Earth's surface
- Moves from west to east (same direction as the Earth spins)
- Has an orbital time period equal to Earth's rotational period of 24 hours
what are uses of geostationary orbits?
- Communications
- GPS
- Satlelite navigation
what is circumpolar orbit?
- the satlelite orbits the earth passing the north and south poles
- orbit is not above the same position just scans the surface of the earth regularly
- orbits a few hundred kilometres above earth
what are uses of circumpolar orbit?
- weather forecasting
- land surveys
- astronomy
What feature is believed to be the thinly spread remains of energy released in the big bang?
Cosmic microwave background radiation- its existence supports the big bang
How do spectra show red shift
The dark lines in the spectra from distant galaxies show an increase in wavelength, the lines are moved or shifted towards the red end of the spectrum
The more red shifted the light from a Galaxy is the _____ the Galaxy is moving away from the earth
Faster
Why are dark lines present when analysing emission spectra from a starbec
Because light from a star doesn't contain all the wavelengths of the e-m spectrum as elements in the star absorb some of the emitted wavelengths so dark lines are present when the spectrum is analysed
Which two things balance and keep a main sequence star in equilibrium
Gravity and radiation pressure
