Name the planets in our solar system in order
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
What is our galaxy called?
The Milky Way
In general, as the distance from the Sun increases:
- the temperature decreases
- the time taken to orbit the Sun increases
What are natural sateillites?
moons that orbit planets
What is the heliocentric model?
the Sun is in the centre of the solar system and all of the planets and other objects in the system orbit the Sun
Why do larger planets have rings?
- they have stronger gravitational field strength so attract debris
What are bigger vs smaller planets made of?
bigger - mostly gas
smaller - mostly rock
How is a planet formed?
For a planet to form, its own gravity must be strong enough to make it round or spherical in shape.
What was the geocentric model?
The Earth was at the centre and planets moved around it.
Sun and moon orbited earth too.
What did we think orbits were like in the past?
- we thought orbits were perfect circes with a fixed backdrop of starts
What is an asteroid?
- made of metals and rocky material
- these orbit the Sun in highly elliptical orbits
What is a comet?
- similar to asteroids, but are made of rocky material, dust and ice
- As a comet approaches the Sun, it begins to vaporise, which means that it turns into a gas. It then produces a distinctive tail
What happens when a sateillite is moving too slowly and too fast?
slow - attraction is too strong and it falls towards Earth
fast - gravitational attraction is too weak and it moves away into space
Evidence for heliocentrism
1) Mars’ retrograde motion. Earth rotates faster than Mars so we undertake it. Appears to reverse its direction in the sky.
2) Galileo observed moons orbiting Jupiter. Shows not everything orbits the Earth
3) Kepler observed planets orbit in ellipses (not circles)
Explain how an orbit works.
- Gravitational force acts on a planet at a right angle to velocity of planet
- causes planet to accelerate towards the sun
- Planet speed doesnt change but it changes direction
- constant change of direction (as it is moving in a circle ish)
- means change in velocity (even if speed is constant)
- This is acceleration of the planet
- Means a force must be acting on it - gravitational force
How does orbit change with distance from the sun?
- The gravitational attraction between two objects decreases with distance.
- This means that the closer the two objects are to each other, the stronger the force of gravity between them.
- If the force between them is greater, a greater acceleration will occur.
- The greater the acceleration, the greater the change in velocity - this causes the object to move faster.
- This means that objects in small orbits travel faster than objects in large orbits.
What are the orbits that artifical sateillites have?
- polar orbits
- geostationary orbits
What is a polar orbit and a geostationary orbit?
Polar - take the satellites over the Earth’s poles. Travel close to Earth at high speeds
Geostationary - higher and more slowly. Take 24 hours to orbit Earth.
Life cycle of a star the same size as the sun/smaller
- Nebula (cloud of dust and gas)
- Gravity causes dust cloud to compress - become more hot and dense
- Forms protostar (high temp and pressure causing nuclear fusion)
- Nuclear fusion keeps the core of the star hot as it releases large amounts of energy
- Protostar becomes a main sequence star (outward pressure caused by fusion balances with outward pressure from mass)
- Forms a red giant (unstable and big)
- Ejects outer laters and becomes a white dwarf
- Cools into a black dwarf
Life cycle of a star bigger than the sun
- Nebula (cloud of dust and gas)
- Gravity causes dust cloud to compress - become more hot and dense
- Forms protostar (high temp and pressure causing nuclear fusion)
- Nuclear fusion keeps the core of the star hot as it releases large amounts of energy
- Protostar becomes a main sequence star (outward pressure caused by fusion balances with outward pressure from mass)
- Forms a red supegiant (fusion occurs with heavier elements, creating elements geavier than iron - causes supergiant to become very big and collapse in on itself - supernova)
- Ejects outer laters
- Forms a neutron star or a black hole
- Forms black hole if it is extremely heavy
What is a black hole?
Extremely dense point in space that has such a strong gravitational field that not even light can escape it.
What is a main sequence star?
stable, with balanced forces keeping it the same size all the time
- gravitational attraction tends to collapse the star
- radiation pressure from the fusion reactions tends to expand the star
- forces caused by gravitational attraction and fusion energy are balanced
What happens in a supernova?
During the majority of a star’s lifetime, hydrogen nuclei fuse together to form helium nuclei. As the star runs out of hydrogen, other fusion reactions take place forming the nuclei of other elements.
Elements that are heavier than hydrogen and helium are formed. Elements heavier than iron are formed in the supernova explosions of high mass stars
When the supernova explodes, all the elements produced are thrown out into the Universe
What is red shift?
the increase in wavelength of light from objects that are moving away from you
observed wavelength is higher than waht it usually is
- light appears red shifted from galaxies moving away from Earth
v=fλ
if λ increases, f must decrease
