Stars & the Universe · revision map · IGCSE 0625, Topic 6.2
TOPIC 6.2 · STARS & THE UNIVERSE
CAMBRIDGE IGCSE PHYSICS 0625 · ONE-PAGE REVISION MAP
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STARS &
UNIVERSE6.2
UNIVERSE6.2
The Sun as a Star
The Sun is an ordinary star, made mostly of hydrogen and helium.
- Its energy comes from nuclear fusion in the core, joining hydrogen nuclei to make helium.
- It stays stable because the outward push of fusion balances the inward pull of gravity.
Life Cycle of a Star
Stars are born, live and die over billions of years. Gravity pulls a cloud together:
nebula → protostar → main sequence
A Sun-like star then becomes a red giant → white dwarf.
A much heavier star (Extended): supergiant → supernova → neutron star or a black hole.
Galaxies & the Light-Year
Our Sun is one star among billions in the Milky Way galaxy.
- The Universe holds billions of galaxies.
- Distances are so vast we use the light-year: the distance light travels in one year.
The Expanding UniverseEXTENDED
Distant galaxies are moving away from us. Their light is shifted to longer, redder wavelengths: this is redshift.
- The further away a galaxy is, the faster it recedes.
- This is evidence the Universe is expanding, and points back to a hot, dense start: the Big Bang.
The Big Bang & the Microwave BackgroundEXTENDED
The expanding Universe traces back to a single hot, dense beginning, the Big Bang, billions of years ago.
- Its leftover glow fills all of space today as the cosmic microwave background radiation (CMBR).
- The CMBR is strong evidence for the Big Bang model of the Universe.
- Together, redshift and the CMBR show the Universe began small and hot and has been expanding ever since.
BUILDS ON · Solar System · The atom
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STARS & UNIVERSE
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LEADS TO · A-Level Astrophysics & Cosmology