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Flashcards · 9203 · Topic 8
Space physics flashcards
20 cards on Topic 8, subtopics 3.8.1 to 3.8.3. Pick a subtopic or study them all.
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3.8.1 Life cycle of a star
- How does a star form?
- Gravity pulls clouds of dust and gas (mainly hydrogen and helium) together; the material gets denser and hotter until hydrogen nuclei fuse. Smaller masses can become planets.
- Why is a main sequence star stable?
- Hydrogen nuclei fuse to helium in the core. The inward pull of gravity is balanced by the outward push of the very hot gas, so the size stays steady. Fusion has not stopped.
- How does a star's mass affect its core and lifetime?
- More mass: stronger gravitational squeeze, so a hotter, denser core that fuses faster and makes heavier nuclei. It uses its fuel faster and has a shorter life.
- Life cycle of a smaller star like the Sun
- Main sequence → red giant (expands, sheds outer layers) → white dwarf (exposed core) → black dwarf (cooled white dwarf).
- Life cycle of a larger star
- Main sequence → red supergiant → supernova → neutron star or black hole (which one depends on mass).
- Where do the elements come from?
- Fusion in stars makes helium, then heavier nuclei. Elements heavier than iron form in a supernova, and the explosion distributes the elements through the universe.
3.8.2 Solar system and orbital motion
- What orbits the Sun, and the planets in order
- Eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune), asteroids, dwarf planets and comets. Moons orbit planets.
- Our place in the universe
- The Sun is a medium-sized star, one of thousands of millions in the Milky Way. The universe has thousands of millions of galaxies.
- Natural vs artificial satellites
- Natural: formed naturally and orbits a planet (e.g. the Moon). Artificial: built and launched, usually orbiting the Earth (e.g. weather or communications satellites).
- Geostationary orbit: features and use
- Above the equator, about 36 000 km up, period 24 hours, moving the same way as the Earth spins, so it stays over one point. Used for communications and TV.
- Low polar orbit: features and use
- A few hundred km up, passing over both poles, period about an hour and a half; the Earth turns beneath it. Used for weather, mapping and whole-surface coverage.
- Why is a body in a circular orbit accelerating at constant speed?
- Gravity provides a centripetal force towards the centre, at right angles to the motion. Its direction changes, so its velocity (a vector) changes: that is acceleration, with no change of speed.
- How does orbital radius affect orbital speed and period?
- A larger radius: weaker gravity, lower speed, longer period. A smaller radius: higher speed, shorter period. Each radius has one stable speed.
- A satellite orbits at radius 8.4 × 10⁶ m, taking 7660 s. Orbital speed?
- v = 2πr/T = 2π × 8.4 × 10⁶ ÷ 7660 = 6890 m/s. Use the radius from the Earth's centre.
3.8.3 Red shift and the expanding universe
- Doppler effect
- A source moving away gives a longer observed wavelength and lower frequency; moving towards, a shorter wavelength and higher frequency. It applies to sound, light and microwaves.
- Red shift, and how it changes with distance
- Light from most distant galaxies has a longer wavelength than expected. The further the galaxy, the bigger the shift, so more distant galaxies are moving away faster.
- How does red shift support the Big Bang model?
- It suggests space itself is expanding. If so, everything was once closer together, supporting the idea that the universe began from one tiny point.
- Cosmic microwave background radiation (CMBR)
- Microwave radiation filling the universe, left over from soon after the universe began. Currently only the Big Bang theory explains it. (Red shift shows expansion; CMBR shows a hot early universe.)
- Approximate age of the universe
- About 14 thousand million years (1.4 × 10¹⁰ years).
- A 486.0 nm line is seen at 487.2 nm in galaxy A and 489.9 nm in galaxy B. Compare them.
- Shifts of 1.2 nm and 3.9 nm; both are red shifts (longer wavelengths). B has the larger shift, so it is moving away faster and is probably further away.