SP7- Astronomy Flashcards
What is the geocentric model
The idea that the sun and all planets orbit the Earth - there is a sphere of fixed stars
It’s a theory by Ptolemy
What’s the heliocentric model
Nicholas Copernicus thought the sun was at the centre of our solar system
What is good about the invention of the telescope to support heliocentric model
We can see new objects - Galilean moons of jupiter , by plotting there movements jt showed not everything orbited earth is Galileo supported Copernicus
What’s our current model of the universe like
8 planets, 5 dwarf planets, thousands of comets and millions of asteroids
These all move in elliptical orbsit around the sun - many of which have natural satellites
Tell me about photography and astronomy
More detailed observations
Computers for analysis
Why are some telescopes placed in space
In order to detect radiation otherwise absorbed by the atomsphere
What is weight
The force of gravity acting on you
What does weight depend on
Gravitational field strength (g)
What’s the gravitational field strength of earth
9.8 N/kg
1kg of mass is 9.81 N
What does the gravitational field strength on the surface of a body surface of a body such as a planet or a moon depend on
Mass of the body and the distance from its centre to its surface (radius)
Greater the mass and smaller it’d radius, greater its surface of gravity
What shape are most bodies orbits in the solar system
Elliptical
Comets are highly elliptical whereas planets can be almost circular
What does the type of orbit an artificial satellite has depend on
What it is used for
For satellites: what are highly elliptical orbits used for
Communication in parts of the earth near the poles
Tell me about a satellite in polar orbit
It will eventually pass over all parts of the world - orbit goes through poles
Tell me about satellites in geostationary circular orbits
They remain over one point on Seth and are used for broadcasting
Tell me about satellites with low earth orbits
Need the least fuel to launch and travel very very fast
Tell me about a satellites speed and velocity
It’s Speed is constant as it travels but it’s direction is changing constantly - an orbiting body has a constantly changing Velocity
Why does gravity change the satellites direction but not speed
A moving object would continue to go in a straight line unless there’s a force acting to make it change speed or direction - the gravitational force between the earth and the satellite is at right angles to the direction of movement so the force changes its direction
Why does a satellite in low orbit have to move much faster to stay in its orbit than a high orbit
If it slows it will fall towards the earth, it will gain speed as it falls and then be fast enough to stay in a new lower orbit where it count encounter the top of the atmosphere and contact with air will make it slow down and fall to earth
What is a nebula
A cloud of dust and gases (mainly hydrogen)
How does a nebula form into a protostar
Materials can be pulled together by their own gravity, as the cloud (nebula) contracts it becomes denser, the hydrogen becomes hotter as it spirals inwards and may start to glow, as more mass is attracted - gravity gets stronger and heats material more - this is a protostar
When does a protostar become a main sequence star
Eventually temperature and pressures in centre of a protostar evoke high enough to force hydrogen nuclei to fuse together and form helium - fusion reactions like this release a lot of energy as electromagnetic radiation, outward pressure from hot gases balance compression from gravity, it’s now in main sequence stage of life awwww
Why does a main sequence star not collapse?! (What is balanced)
Pressures from hot gases and compression due to gravity
When does a red giant form after a main sequence
When they have fused most of their hydrogen into helium, the core core is not hot enough to withstand gravity and it collapses - outer layers expand to form a red giant
How does a red giant survive
Other fusion happens - convincing helium Nuclei to form heavier elements
When does a white dwarf form
When a red giant throws off a shell of gas, the rest of the star is pulled together by gravity and collapses to form a white dwarf - no fusion happens in a white dwarf
When does a black dwarf form
After a white dwarf, there’s no fusion so gradually it cools over about 1 billion years
Tell me just the names of the stages of the life cycle of a star the size of our sun
Cloud of gas -> protostar-> main sequence star -> red giant -> shell of gas -> white dwarf -> black dwarf
What’s different in the stages of a massive main sequence star
When a main sequence has considerable more mass than the sun, they fuse helium into to hydrogen faster and are brighter and hotter, they become red supergiants and after rapidly collapse and explode into a supernova. The outer layers are cast off and expand outwards
What happens after a supernova ?
If what is left is 4x or more the mass of sun, gravity pulls remains together to form a black hole
If the remains are not so massive - gravity pulls them together to form a very dense star called a neutron star
The gravitational pull of a black hole is so strong not even….
Light can escape!!!
What is the principle of the Doppler effect
The pitch of a sound depends on the frequency of the wave - sound waves behind a moving vehicle /source become stretched to make the wavelength longer to lower frequency, opposite happens when source of sound is in front
This opposite happenw if the source of the sound is moving relative to the observer, if you are travelling in a car with the same speed the sound would not change idiot #basic
How are light waves redshifted
Similar to the Doppler effect - lines are moved toward the red end of the spectrum, the star is moving a way from us - the more the lines are shifted, the faster the star is moving
The redshift is a measure of how far along the spectrum the lines have moved
What happens when pattern of lines move towards the blue spectrum
The star must be moving towards us as the wavelength and frequency of the light waves become shorter and so the pattern of lines move towards the blue end of the spectrum
How did Edwin Hubble use redshift to show the universe is expanding
Investigated pattern of line shifted for 50 galaxies in comparison to the sun, discovered almost all were red shifted and moving away - further away the galaxy, the greater the redshift and so faster it’s moving away from us - interpret this relationship to mean that the universe is expanding
What is the Big Bang theories
First suggested in the 1920s - says that the whole universe and all the matter in it started out as a tiny point of concentrated energy 13.5 billion years ago, it expanded from this point and is still expanding
As the universe expanded, gravity caused matter to clump together to form stars
What’s the steady state theory
Suggested in 1948, theory says the universe has always existed and is expanding, new matter is continuously created within the universe as it expands
What is cosmic microwave background radiation
The big band states that huge amounts of radiation were released at the beginning of the universe, becuase the universe is expanding, wavelength has increased so it’s only detectable as microwave radiation
What universe creation story is most believed
Both the steady state and Big Bang theory say the universe is expanding - redshift support both
But CMB shows evidence for Big Bang only, steady state can’t explain it so since there’s more supporting evidence for Big Bang is more widely accepted
