Cognito · AQA Physics 2026/27The Universe and Red-Shift
Key facts
The solar system and universe
Solar system: Sun + 8 planets + moons, asteroids, comets.
Galaxy: billions of stars held together by gravity. Milky Way is our galaxy.
Universe: billions of galaxies.
Distances measured in light-years: 1 light-year = distance light travels in one year.
Planets orbit the Sun due to gravitational attraction. Closer planets: shorter orbital period, faster speed.
Life cycle of stars
Small star (like our Sun): nebula → protostar → main sequence → red giant → white dwarf → black dwarf.
Large star: nebula → protostar → main sequence → red supergiant → supernova → neutron star OR black hole.
Main sequence: hydrogen fusion balances gravity. This phase lasts billions of years.
Supernova: massive explosion that produces elements heavier than iron — distributed through universe.
Red-shift and the Big Bang
Red-shift — light from distant galaxies is shifted towards the red (longer wavelength) end of the spectrum.
Indicates galaxies are moving away from us. The further the galaxy, the greater the red-shift.
This is evidence the universe is expanding.
Big Bang theory — universe began from a very hot, dense point ~13.8 billion years ago and has been expanding ever since.
Evidence: red-shift of galaxies, cosmic microwave background radiation (CMB) — a faint glow of radiation throughout the universe, remnant of the Big Bang.
Exam questions — 4 questions · 12 marks
⚡ Extended questions included. Show all working for calculation questions. The AI marks against the real AQA mark scheme.
1 markRed-shift evidenceAQA 8463 P2 style
What does the red-shift of light from distant galaxies tell us about the universe?
A The universe is contracting and all galaxies are moving towards us
B The universe is expanding — distant galaxies are moving away from us
C The temperature of distant galaxies is decreasing
D Distant galaxies have different chemical compositions to our galaxy
4 marksLife cycle of a large starAQA 8463 P2 style
Describe the life cycle of a star much more massive than the Sun from protostar to its final state. (4 marks)
Hint: Follow the sequence: nebula → protostar → main sequence → red supergiant → supernova → neutron star/black hole. The more massive the star, the more dramatic the ending.