The Sun and Earth
The Sun is a star, a huge ball of hot gas. Almost all the light and heat on Earth comes from it. Earth is the third planet from the Sun, at just the right distance for liquid water and life. Sunlight takes about eight minutes to reach us.
Day and night
Earth rotates (spins) on its axis once in about 24 hours. At any moment half of Earth faces the Sun (day) and half faces away (night). The Sun seems to move across the sky, but it is Earth that turns.
Year and seasons
Earth revolves (goes round) the Sun once in about 365 days. Its axis is tilted about 23.5 degrees and points the same way in space all year.
- In June the north leans toward the Sun: long days, strong sunlight, summer in the north and winter in the south.
- In December it is the other way round.
- In March and September day and night are nearly equal.
Seasons come from the tilt, not from Earth being nearer or farther from the Sun.
Landscapes: mountains, plains, rivers
Earth's crust is broken into big pieces called plates that float on hot, slowly flowing rock and move a few centimetres a year. When two plates push together, land can fold up into mountains. Rivers and rain wear land down, carry soil and build flat plains. Wind, ice and waves also shape the land and the coast.
Natural disasters and staying safe
- Earthquake: plates slip and the ground shakes. During shaking, drop, cover under a strong table and hold on. Stay away from windows.
- Volcano: hot melted rock and ash come out. Follow evacuation advice.
- Flood: heavy rain or a swollen river covers land. Move to high ground. Do not walk or drive through floodwater.
- Cyclone: a strong spinning storm from warm seas. Stay indoors and follow warnings.
Early warnings, drills, strong buildings and a family emergency kit save lives.
Try it
In a dark room, hold a torch (the Sun) and turn a ball (Earth) slowly. Stick a pin on it and see when it is in light and in shadow. Then tilt the ball and walk it round the torch, keeping the tilt pointing the same way, and notice when the top gets more light.
Key formulas and definitions
- Rotation: 24 hours = 1 day-night cycle
- Revolution: about 365 days = 1 year
- Axis tilt: about 23.5 degrees
- Seasons are caused by the tilt
Worked examples
1. Earth turns 360 degrees in 24 hours. How many degrees per hour?
360 / 24 = 15 degrees per hour.
2. It is June. Which hemisphere has summer, and why?
The northern hemisphere. Its half of Earth is tilted toward the Sun, so it gets longer days and more direct light.
3. A plate moves 4 cm a year. How far in 1000 years?
4 x 1000 = 4000 cm = 40 m.
Common mistakes
- Thinking seasons happen because Earth is closer to the Sun in summer.
- Mixing rotation (day and night) with revolution (year).
- Thinking the Sun moves round Earth.
- Hiding near windows or running outside during an earthquake instead of drop, cover, hold.