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Work through the notes, try the practice questions, then take the quiz. The report tells you exactly what to revise next. (2026)
Question
State the eight planets of our solar system in order from the Sun.
Solution
Use a mnemonic such as My Very Easy Method Just Speeds Up Naming.
Answer
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
Question
Identify whether each of the following is a planet, a dwarf planet, a moon, an asteroid or a comet: (a) Ceres, (b) Titan, (c) Halley's, (d) Neptune.
Solution
Ceres lies in the asteroid belt and is the largest object there. It is classed as a dwarf planet.
Titan orbits Saturn — a moon (natural satellite).
Halley's has a highly elliptical orbit and develops a tail near the Sun — a comet.
Neptune is the eighth planet from the Sun.
Answer
(a) Dwarf planet (b) Moon (c) Comet (d) Planet.
Question
Describe how the Sun was formed (4 marks).
Solution
Start with the nebula.
Gravity pulled it together.
Heat and pressure built up.
Fusion began.
Answer
A nebula (cloud of dust and gas) was pulled together by gravity, heating up into a protostar; when the core became hot and dense enough, nuclear fusion of hydrogen into helium began and a stable star (the Sun) formed.
Question
Explain why a star on the main sequence is stable (3 marks).
Solution
Identify the inward force.
Identify the outward force.
Balance.
Answer
The inward gravitational force is balanced by the outward force from radiation pressure (from nuclear fusion), so the star neither collapses nor expands.
Question
A star much more massive than the Sun reaches the end of its life. State the remaining stages.
Solution
After main sequence, massive stars expand.
They explode.
Remnant.
Answer
Red super giant → supernova → neutron star (or black hole).
Question
Gold (Au, atomic number 79) is heavier than iron. Explain how gold atoms come into existence.
Solution
Fusion in main sequence and giant stars only makes elements up to iron.
A massive star ends its life in a supernova.
In the explosion, energies are high enough to fuse lighter nuclei into much heavier ones, including gold.
The supernova then scatters these elements across space.
Answer
Gold is formed during a supernova explosion — the only conditions in the universe in which elements heavier than iron can be made — and is then distributed across space.
Question
A satellite moves in a stable circular orbit at constant speed. Explain why the satellite is accelerating (3 marks).
Solution
Define velocity.
Direction changes.
Therefore velocity changes.
Answer
Velocity is a vector — it depends on direction as well as speed. In a circular orbit the satellite's direction is continuously changing, so its velocity changes, so it is accelerating (even though speed is constant).
Question
Satellite A orbits Earth at 400 km altitude. Satellite B orbits at 36 000 km altitude (geostationary). Which satellite moves at the greater orbital speed, and why?
Solution
Closer orbit → stronger gravity → larger centripetal force required.
To match the required centripetal force at a small radius, speed must be higher.
Answer
Satellite A (the lower one) moves faster (~7.7 km/s vs ~3.1 km/s). A stable circular orbit at a smaller radius requires a higher orbital speed.
Question
Give two everyday uses of artificial satellites.
Solution
Communications: TV signals, satellite phones.
Navigation: GPS.
Answer
Examples include: communications (TV, satellite phone), navigation (GPS), weather monitoring, Earth observation (e.g. monitoring deforestation), and space telescopes such as Hubble.
The Sun together with all the objects held in orbit around it by its gravity — planets, dwarf planets, moons, asteroids and comets.
A huge collection of stars held together by gravity. Our galaxy is the Milky Way.
A naturally occurring object (e.g. a moon) in orbit around a planet.
A cloud of dust and gas in space — the starting point for the formation of stars.
A cloud of dust and gas in space — the birthplace of stars.
A hot, dense core formed from a collapsing nebula; not yet fusing hydrogen.
A stable star in which hydrogen is fusing into helium; gravity is balanced by outward radiation pressure.
An expanded, cooler star formed when a star's core hydrogen runs out. Super giant if very massive.
The explosive death of a high-mass star; forms elements heavier than iron and distributes them through space.
The hot, dense core left behind when a Sun-like star sheds its outer layers.
An extremely dense remnant left after a supernova, made mostly of neutrons.
The remnant of a very massive star where gravity is so strong even light cannot escape.
The resultant force on an object moving in a circular path, directed towards the centre of the circle. For orbits, this force is gravity.
The (approximately circular or elliptical) path of one body around another due to gravity.
A naturally occurring body in orbit around a planet — i.e. a moon.
A human-made object placed in orbit, used for communications, navigation, observation or science.
Mistake
Listing Pluto as a planet.
Why it happens
Older textbooks still call it one.
How to avoid it
Pluto has been a dwarf planet since 2006 (IAU).
Mistake
Saying the Sun 'burns' hydrogen.
Why it happens
Everyday language.
How to avoid it
The Sun's energy comes from nuclear FUSION, not combustion.
Mistake
Calling the Sun the centre of the galaxy or the universe.
Why it happens
Confusing the hierarchy.
How to avoid it
The Sun is the centre of OUR SOLAR SYSTEM; it is just one star in the Milky Way.
Mistake
Mixing up the two pathways (e.g. Sun → supernova).
Why it happens
Not noting the mass.
How to avoid it
Sun-sized → white dwarf. Much larger → supernova.
Mistake
Claiming a normal star can fuse anything up to gold or uranium.
Why it happens
Forgetting the iron limit.
How to avoid it
Stellar fusion stops at iron. Heavier elements need a supernova.
Mistake
Saying a high-mass star ends as a white dwarf.
Why it happens
Confusion of remnants.
How to avoid it
White dwarf = low mass remnant; neutron star/black hole = high mass remnant.
Mistake
'Constant speed means no acceleration.'
Why it happens
Equating speed and velocity.
How to avoid it
Velocity is a vector; if direction changes, velocity changes, so there IS acceleration.
Mistake
Thinking lower orbits are slower.
Why it happens
Intuition (gravity feels 'stronger').
How to avoid it
Lower orbit needs HIGHER speed to balance the stronger gravity — ISS at 7.7 km/s, geostationary at 3.1 km/s.
Mistake
Saying 'there is no force on a satellite because nothing is pulling it'.
Why it happens
No visible string.
How to avoid it
Gravity acts at a distance — there's always a gravitational force pulling the satellite towards the body it orbits.