IGCSE 0625 · SPACE · 6.2

Stars and the Universe

The Sun as a fusion-powered star, the life cycle of stars, galaxies and the light-year, and the Extended ideas of redshift, the expanding Universe, and the Big Bang. It builds on the Solar System and the atom.

TOPIC 6.2: STARS AND THE UNIVERSE CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 6.1 Solar System 5.1 The atom LEADS TO Cosmology The Big Bang STARS & UNIVERSE 1 · THE SUN AS A STAR The Sun is an ordinary star. It is 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. H → He fusion releases energy 2 · LIFE CYCLE OF A STAR Stars are born, live, and die over billions of years. Gravity pulls a cloud of gas and dust together into a protostar, then a main-sequence star. nebula protostar main sequence A Sun-like star then becomes: red giant white dwarf A much heavier star (Extended): supergiant supernova neutron star or a black hole 3 · GALAXIES & DISTANCES Our Sun is one star among billions. The Sun belongs to 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 Milky Way is a spiral galaxy 4 · THE EXPANDING UNIVERSE EXTENDED 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 points back to a hot, dense start: the Big Bang. Its leftover glow is the cosmic microwave background radiation (CMBR). us the further away, the faster
TOPIC 6.2: STARS AND THE UNIVERSE CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 6.1 Solar System 5.1 The atom LEADS TO Cosmology The Big Bang STARS & UNIVERSE 1 · THE SUN AS A STAR The Sun is an ordinary star. It is 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. H → He fusion releases energy 2 · LIFE CYCLE OF A STAR Stars are born, live, and die over billions of years. Gravity pulls a cloud of gas and dust together into a protostar, then a main-sequence star. nebula protostar main sequence A Sun-like star then becomes: red giant white dwarf A much heavier star (Extended): supergiant supernova neutron star or a black hole 3 · GALAXIES & DISTANCES Our Sun is one star among billions. The Sun belongs to 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 Milky Way is a spiral galaxy 4 · THE EXPANDING UNIVERSE EXTENDED 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 points back to a hot, dense start: the Big Bang. Its leftover glow is the cosmic microwave background radiation (CMBR). us the further away, the faster
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