Earth, space and the wider environment
Earth, space and the wider environment tests the solar system, Earth-Sun-Moon relationships and environmental chemistry/physics.
Earth and space
- The solar system has the Sun, eight planets, dwarf planets, moons, asteroids and comets. Gravity provides centripetal force for orbits; closer orbits are faster.
- Seasons are caused by Earth's axial tilt, not distance from the Sun. The Moon orbits Earth; phases depend on the Sun-Moon-Earth angle. Solar eclipse: Moon between Sun and Earth. Lunar eclipse: Earth between Sun and Moon.
- Stars form from gas and dust; the Sun is a main-sequence star; galaxies contain stars; the universe is expanding.
Earth and environment
- Earth has core, mantle, crust; tectonic plates move and cause earthquakes/volcanoes.
- Atmosphere: nitrogen about 78%, oxygen about 21%, argon, carbon dioxide. Greenhouse gases absorb infrared and warm the surface; ozone absorbs ultraviolet.
- Carbon cycle: photosynthesis, respiration, combustion, dissolution. Human activities increase CO2 and methane.
- Resources: finite fossil fuels, recycling, water treatment, pollution control.
Worked example
Explain why summer occurs in the northern hemisphere. It is not because Earth is closer to the Sun; Earth's axis is tilted about 23.5°, so the northern hemisphere receives sunlight at a higher angle and for longer days, increasing energy per area. The same tilt causes winter when the northern hemisphere is tilted away.
Traps
Saying seasons are caused by distance; confusing phases with eclipses; saying the Moon produces light; reversing eclipse order; thinking the greenhouse effect is entirely harmful.