What is a planet?
A large object that orbits a star
What are the planets in our Solar System, in order of distance from the Sun?
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
What are dwarf planets?
Planet-like objects that aren’t big enough to be classified as planets
What are moons?
Natural objects that orbit planets with almost circular orbits
What is a satellite?
An object that orbits a second, more massive object
What are asteroids?
Lumps of rock and metals that orbit the Sun, usually found in the asteroid belt
What are comets?
Lumps of ice and dust that orbit the Sun. Their orbits are usually highly elliptical - some travel from near the Sun to the outskirts of the Solar System.
What causes orbits?
Gravity causes a centripetal force, acting towards the centre of the orbit. This force would cause the object to fall towards what it was orbiting, but as it is already moving, it just causes it to change direction. It is accelerating towards what it’s orbiting but the instantaneous velocity, at a right angle to acceleration, keeps it travelling in a circle.
What does gravity depend on?
The mass of the body creating the field - the larger the mass, the stronger the force
Distance - the closer you get, the stronger the force
How and why does speed vary with orbit distance?
The closer the orbit, the faster the object moves. This is because the centripetal force from gravity is larger, so the instantaneous velocity also needs to be larger to balance it.
How has the model for the Solar System changed over time?
Ancient Greeks - 1500s: Geocentric model
1500s - present: Heliocentric model
Later we realised planet orbits are elliptical rather than circular and the Sun is not at the centre of the universe
What is the geocentric model?
The theory that said the Sun, Moon, planets and stars all orbited the Earth in perfect circles. People had no telescopes and saw everything travelling across the sky in the same way every day and night.
What is the heliocentric model?
The theory that the Earth and planets all orbited the Sun in perfect circles
What was Galileo’s evidence for the heliocentric model?
He looked at Jupiter with a telescope and noticed some ‘stars’ in a line near the planet (Jupiter’s moons). When he looked again, he found that they never moved away from Jupiter and seemed to be carried along with it. This showed that not everything orbited Earth, so that the geocentric model was wrong.
What is the Steady State theory?
The theory that the Universe has always existed as it is now, and it always will do. The Universe appears pretty much the same everywhere. As it expands, new matter is constantly being created, so the Universe’s density is always roughly the same. There is no beginning or end to the Universe.
What is the Big Bang theory?
The theory that initially all the matter in the Universe occupied a very small space, which was very hot and dense. This then ‘exploded’ - space started expanding, and this expansion is still going on. There is a finite age for the universe: ~13.7 billion years.
What is the Doppler effect?
When an object is travelling towards you wavelengths of sound are bunched together, so the frequency of sound seems higher. When an object is travelling away from you wavelengths of sound are spread further apart, so the frequency of sound seems lower.
What is red-shift and what does it suggest?
Absorption spectra from distant galaxies have the same patterns as ones from elements on Earth, but at slightly lower frequencies, with more light coming with increased wavelengths. The patterns are shifted towards the red end of the spectrum: red-shift. This shows that they are moving away from us, as with the Doppler effect. More distant galaxies have greater red-shifts, so are moving away faster. This suggests that the Universe is expanding.
What is CMB radiation?
Cosmic microwave background radiation - low frequency electromagnetic radiation coming from all parts of the Universe, mostly in the microwave part of the EM spectrum.
Why is the Big Bang theory the currently accepted model?
Red-shift supports both models, but CMB radiation shows the Universe had a beginning so only supports the Big Bang theory. In the theory it is the leftover energy of the initial explosion.
What is the life cycle of a star about the size of the Sun?
Nebula Protostar Main sequence star Red giant White dwarf
What is the life cycle of a star much larger than the Sun?
Nebula Protostar Main sequence star Red supergiant Supernova Neutron star or black hole
What is a nebula?
A cloud of dust and gas that will become a star
What is a protostar?
A cloud of dust and gas pulled together by gravity. As it gets denser, the temperature rises until it is hot enough for hydrogen to perform fusion, creating a star.
What is a main sequence star?
A long, stable period in a star’s lifespan where hydrogen undergoes fusion. It typically lasts several billion years; the heavier the star, the shorter this period.
What is a red giant or supergiant?
When hydrogen in the core begins to run out, the star is compressed by gravity as thermal expansion decreases. When it is dense and hot enough that the energy created makes the outer layers of the star expand, it becomes a red giant or supergiant depending on the size. The surface cools so it turns red.
What is a white dwarf?
A hot, dense solid core created when a small to medium sized star (e.g. the Sun) becomes unstable and ejects its outer layer of dust and gas.
What is a supernova?
The explosion of a red supergiant. It occurs after it begins to undergo more fusion to make heavier elements. They expand and contract several times as the balance shifts between gravity and thermal expansion before the explosion.
What is a neutron star?
A very dense core created after a smaller red supergiant’s supernova, when its outer layers of dust and gas have been ejected.
What is a black hole?
An extremely dense point in space that not even light can escape from, created after a larger red supergiant’s supernova, when its outer layers of dust and gas have been ejected and it collapses.
How can you improve the quality of an image produced by a telescope without moving it?
Increase its aperture, the diameter of the objective lens
Use a higher quality objective lens
Why do telescopes on Earth, especially in urban areas, get worse images than those in space?
The atmosphere gets in the way, absorbing lots pf light coming from space
Light pollution (light from objects on Earth in the atmosphere) makes it hard to pick out dim objects
Air pollution can reflect and absorb light coming from space
How have telescopes improved over time?
1500s: optical telescopes, using visible light to see close objects
1940s: telescopes for all parts of the EM spectrum e.g. X-ray telescopes for high-temperature events and radio telescopes, which discovered CMB radiation
Telescopes with greater resolution and magnification
Use of computers to analyse and store data