8 Astrophysics

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).

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

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

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

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

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

Understand how stars can be classified according to their colour

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

Describe the evolution of stars of similar mass to the Sun through the following stages:

• nebula
• star (main sequence)
• red giant
• white dwarf

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

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

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

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

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

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

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

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

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