Astrophysics Flashcards
(21 cards)
What is a universe
A collection of billions of galaxies
What is a galaxy
A large collection of stars
What is a planet
Large objects that orbit a star
What are moons
Objects that orbit planets
What is the difference between asteroids and comets
Asteroids are lumps of rock and metal that orbit the sun
Comets are lumps of ice and dust that orbit the sun
How does gravity keep an object in orbit
The force acts towards the centre of the object it is orbiting
As the object is moving, this force causes it to change direction
The object keeps accelerating but the instantaneous velocity keeps it travelling in a curved path round the object
How does the force due to gravity depend on mass and distance
The larger the mass of the body, the stronger its gravitational field
The closer you are to a star or planet, the stronger the gravitational force is
The stronger the force is, the larger the instantaneous velocity needed to balance it
What type of orbit to comets have
Very elliptical
What is the use of geostationary satellites
Communications as they are always over the same part of the planet as they have an orbital period of exactly 1 day
Describe the process of a nebula transforming into a white dwarf
Cloud of dust and gas called a nebula is pulled together by gravity to form a protostar
As the temperature rises due to increased density, hydrogen nuclei undergo nuclear fusion which gives out a huge amount of energy which causes the core of the star to rise in temperature
A main sequence star experiences a stable period due to outward pressure caused by thermal expansion balancing the force of gravity
The star compresses and expands to form a red giant, it becomes unstable per and ejects its outer layer of dust and gas to leave behind a hot, dense, solid core, a white dwarf is formed
What is thermal expansion
The energy produced by nuclear fusion trying to expand the star
What causes the time spend as a main sequence star to decrease
Increasing the heaviness of the star
Describe the process of a main sequence star into a neutron star or black hole
If the star is larger, following expansion from the compression, a red super giant is formed
The star stars to undergo more fusion causing increased brightness and heavier elements to be produces, they expand and contract several more times and they eventually explode in a supernova
The exploding supernova throws the dust and gas into space, leaving a very dense core called a neutron star behind
If the star is massive enough, it will collapse and become a black hole, which not even light can escape from
State the colours of star in decreasing temperature
Blue
White
Yellow
Orange
Red
What causes higher frequencies of light to be emitted by a star
Increased temperature
What is absolute magnitude
A measurement of how bright a star is from a set distance from Earth
The lower the value the brighter it is
And it is increased by increasing size and temperature
What is red-shift
The light emitted by a source moving away from you which shifts towards the red end of the EM spectrum
What evidence shows that light from galaxies is red-shifted
Different elements absorb different frequencies of light
When light is passed through an element, a pattern of dark lines is produced at each of the frequencies in the visible part of the EM spectrum that the element absorbs
When we look at light from distant galaxies, we see the same patterns but at slightly lower frequencies
The light has been shifted to the red side
How does red-shift suggest that the universe is expanding
Measurements suggest that all galaxies are moving away from us very quickly regardless of the direction you look in
More distant galaxies have greater red shifts than nearer ones, they show a bigger observed increase in wavelength
This shows that more distant galaxies are moving away faster than nearer ones
This suggests that the universe is expanding
What if cosmic microwave background radiation
Low frequency microwave radiation coming from all directions and parts of the universe
How does CMB radiation provide evidence for the Big Bang theory
Initially all the matter in the universe occupied a single point
This tiny space was very dense and very hot
This point then exploded and caused expansion
The expansion is still going on
