What is the geocentric (Ptolemaic) model?
Planets move in small circles called epicycles and the center of the epicycle moves along a larger circle around the Earth. Stars are fixed on an outermost sphere. Model gives predictions on the positions of planets within a few degrees from the actual positions.
What is the heliocentric model?
A model created by Nicolaus Copernicus where the Sun was the center of the solar system and all the planets were in the correct order up to Saturn. Proof of this model was backed up by Newton (gravity discovery) and Galileo.
How do planets orbit?
In ellipses.
What did Galileo discover?
- There were 4 moons orbiting around Jupiter
- Venus went through phases like our moon
- Celestial bodies are not perfect and eternal
What are the characteristics of asteroids?
- Mainly composed of mineral rock
- Formed closer to the Sun
- Diameter greater than 1m
What are the characteristics of comets?
- Mainly composed of dust and ice
- Long, elliptical orbits
What are the characteristics of meteoroids?
- Diameter of 1m or less
- Can be composed of either cometary or asteroidal materials
What is a meteorite?
A meteoroid that survives its passage through the Earth’s atmosphere and lands upon the Earth’s surface.
What is a star?
A ball of plasma undergoing nuclear fusion. They give off large amounts of energy in the form of electromagnetic radiation.
What are the different stages in the life cycle of a star?
- Nebula
- Protostar
- Main sequence star
- Red giant
- White dwarf
- Black dwarf
What are the different stages in the life cycle of a large star?
- Nebula
- Protostar
- Main sequence star
- Red super giant
- Supernova
- Black hole or neutron star
What happens in the nebula stage?
- Nebula is a cloud of dust and gases (mainly hydrogen)
- These materials can be pulled together by their own gravity
- As the cloud contracts it becomes denser
- Hydrogen becomes hotter as it spirals inwards and may start to glow
What happens in the protostar stage?
As more mass is attracted, the cloud’s gravitational pull gets stronger and heats the material even more.
What happens in the main sequence stage?
Eventually the temperatures and pressures in the centre of the protostar become high enough to force hydrogen nuclei to fuse together and form helium. Fusion reactions like this release a lot of energy as E/M radiation which balances the compression due to gravity with the outward pressure from the hot gases.
What happens in the red giant stage?
- At some point, all hydrogen of the star will convert into helium
- Collapsing outer layers cause core to heat up
- Fusion of helium into carbon begins
- Forces regain balance
- Outer shell expands from 1 to at least 40 million miles across
- Red giants last for about 1 billion years
What happens in the white dwarf stage?
1.Star throws off a shell of gas and rest of the star is pulled together by gravity, collapsing to form a white dwarf star
2. The pressure exerted on the core by the outer layers does not produce enough energy to start carbon fusion
3. The core is now very dense and hot
4. White dwarf is about 8000 miles in diameter and after 35000 years the core begins to cool
5. White dwarf gradually cools over about a billion years to become a black dwarf
What happens in the black dwarf stage?
- As white dwarf cools, the light it gives off will fade through the visible light spectrum, blue to red to black (no light)
- A black dwarf will continue to generate gravity and low energy transmissions
What happens in the red supergiant stage?
- If mass of star is 3x that of our sun or greater, Red Giant will become a Red Supergiant
- When a massive red giant fuses all of the helium into carbon, fusion stops and outer layers collapse on core
- This time there is enough mass to get the core hot enough to start fusion of carbon into iron
- Once fusion begins, star will expand between 10-1000x larger than our sun
What happens in the supernova stage?
- When a supergiant fuses all carbon into iron, there is no more fuel left to consume
- Core will collapse in less than a second causing a massive explosion (supernova)
- In a supernova, a massive shockwave is produced that blows away outer layers of the star
- Supernova will shine brighter than whole galaxies for a few years
What happens in the neutron star/black hole stage?
Neutron star: Remains of core may contract to form an incredibly dense, fast-spinning star the size of a city. All matter is crushed to form neutrons.
Black hole: Cores of the most massive stars collapse to form a black hole - a region in which gravity is so strong that not even light can escape its pull.
