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8 Astrophysics

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  1. Astrophysics units

    1. Use the units kilogram (kg), metre (m), metre per second (m/s), metre per second squared (m/s²), newton (N), second (s) and newton per kilogram (N/kg).

  2. (b) Motion in the universe

    1. Know that: • the universe is a large collection of billions of galaxies • a galaxy is a large collection of billions of stars • our solar system is in the Milky Way galaxy

    2. Understand why gravitational field strength, g, varies and know that it is different on other planets and the Moon from that on the Earth

    3. Explain that gravitational force: • causes moons to orbit planets • causes the planets to orbit the Sun • causes artificial satellites to orbit the Earth • causes comets to orbit the Sun

    4. Describe the differences in the orbits of comets, moons and planets

    5. Use orbital speed = 2π × orbital radius ÷ time period, v = 2πr/T.

  3. (c) Stellar evolution

    1. Understand how stars can be classified according to their colour

    2. Know that a star’s colour is related to its surface temperature

    3. Describe the evolution of stars of similar mass to the Sun through the following stages: • nebula • star (main sequence) • red giant • white dwarf

    4. Describe the evolution of stars with a mass larger than the Sun

    5. Understand how the brightness of a star at a standard distance can be represented using absolute magnitude

    6. Draw the main components of the Hertzsprung–Russell diagram (HR diagram)

  4. (d) Cosmology

    1. 8.13PBig Bang theory

      Describe the past evolution of the universe and the main arguments in favour of the Big Bang theory

    2. 8.14PBig Bang evidence

      Describe evidence that supports the Big Bang theory (red-shift and cosmic microwave background - CMB - radiation)

    3. 8.15PMoving wave sources

      Describe that if a wave source is moving relative to an observer, there will be a change in the observed frequency and wavelength

    4. 8.16PRed-shift equation

      Use change in wavelength ÷ reference wavelength = galaxy velocity ÷ speed of light: Δλ/λ₀ = v/c, where Δλ = λ − λ₀.

    5. 8.17PGalaxy red-shift

      Describe the red-shift in light received from galaxies at different distances away from the Earth

    6. 8.18PExpansion of the universe

      Explain why the red-shift of galaxies provides evidence for the expansion of the universe