This grade 6 science lesson on solar system notes gives the key ideas first, then worked examples and diagrams. After that, practise with the worksheet on solar system and check yourself with the quiz.
Quick answer: The solar system is the Sun with the eight planets that orbit it, held in place by the Sun’s gravity. The Earth spins once in 24 hours, giving day and night, and orbits the Sun in about 365 days. Its axis is tilted by 23.5°, and this tilt, not distance, causes the seasons.
Level: Grade 6 science (Year 7 · Class 6) · Curriculum: MS-ESS1-2
Solar system notes: the key ideas
What is in the solar system?
The solar system is the Sun and everything that travels around it. The Sun is a star, a huge ball of hot gas that gives out light and heat. Eight planets orbit the Sun, together with moons, dwarf planets, asteroids and comets.
An orbit is the curved path of one object around another. The Earth rotates (spins) on its axis and revolves (orbits) around the Sun.
| Planet | Type | Time for one orbit |
|---|---|---|
| Mercury | Rocky | 88 days |
| Venus | Rocky | 225 days |
| Earth | Rocky | 365 days |
| Mars | Rocky | 687 days |
| Jupiter | Gas giant | 11.9 years |
| Saturn | Gas giant | 29.5 years |
| Uranus | Ice giant | 84 years |
| Neptune | Ice giant | 165 years |
The farther a planet is from the Sun, the longer its journey takes. Earth is about 150 million km from the Sun. Light covers that distance in about 500 seconds, or 8 minutes 20 seconds.
Why do we have day and night?
The Sun lights only half of the Earth at any moment. The Earth spins once every 24 hours, so a place is carried into the sunlit half (day) and then into the dark half (night). The Sun does not move across the sky; we move. The Earth spins from west to east, which is why the Sun appears to rise in the east.
One full rotation takes 24 hours, so the Earth turns 15° every hour (360° ÷ 24 h).
Fatima in Dubai is at 55° east and Liam in Dublin is at 6° west. The difference is 61°. How big is the time difference?
Rate: 360° ÷ 24 h = 15° per hour. Time: 61° ÷ 15° per hour = 4.07 h. About 4 hours; Dubai is ahead.
Why do we have seasons?
The axis of the Earth is tilted by 23.5°. In June the northern half leans toward the Sun, so the Sun climbs high, the days are long and sunlight is concentrated: it is summer in the north and winter in the south. Six months later the northern half leans away and the pattern reverses. Near the equator the Sun is always high, so the seasons are weak and day length stays close to 12 hours.
Seasons are not caused by Earth being closer to the Sun in summer. In fact the Earth is closest to the Sun in early January, when it is winter in the north.
What keeps the planets in orbit?
Gravity from the Sun pulls every planet toward it. A planet also moves sideways at great speed. Gravity keeps bending its path inward, so the planet curves around the Sun instead of flying away. If gravity stopped, the planet would move off in a straight line. If the planet stopped moving sideways, it would fall into the Sun.
Hiroshi is 12 years old. Mercury orbits the Sun in 88 days. How many Mercury years is that?
Days lived: 12 × 365 = 4380 days. Mercury years: 4380 ÷ 88 = 49.8. About 50 Mercury years.
Use your fist as the Sun and a ball as the Earth. Spin the ball for day and night, then walk it around your fist with the axis tilted for the seasons.
- The Earth rotates once in 24 hours (15° per hour) and orbits the Sun in about 365 days.
- The Earth’s axis is tilted by 23.5°, which causes the seasons.
- The Sun’s gravity keeps the planets in orbit.
- Earth is about 150 million km from the Sun; light takes about 500 s to arrive.
- Eight planets: four rocky inner planets and four giants.
Earth, day, seasons and orbits: frequently asked questions
Why does the Earth have day and night?
The Earth spins on its axis once every 24 hours. The half facing the Sun has day while the other half has night. The Sun only seems to move across the sky because we are turning.
What causes the seasons?
The tilt of the Earth’s axis by 23.5° causes the seasons. When a hemisphere leans toward the Sun it receives more direct sunlight and longer days, so it has summer. The distance to the Sun is not the cause.
What keeps the planets in orbit around the Sun?
The Sun’s gravity pulls planets inward, while their sideways motion carries them forward. The two together make a curved path around the Sun. Without gravity a planet would fly off in a straight line.
How many planets are in the solar system?
There are eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The first four are small and rocky, and the last four are large giants made mostly of gas and ice.
How long does Earth take to orbit the Sun?
The Earth takes about 365 days to orbit the Sun once, which is one year. It takes 24 hours to spin once on its axis, which is one day. Planets farther out take longer to orbit.
