Moonshot

Moonshot: Earth's orbit and gravity for Cambridge IGCSE Marine Science

This free game is part of our Cambridge iGCSE Marine Science (0697) course for exams in EXAM YEARS 2027-2029.

Planets, natural satellites and orbits

In Moonshot you run the Orbit Lab simulator. You pull back and launch the Moon into orbit round the Earth, then the Earth into orbit round the Sun, with gravity that works like the real thing. It covers the start of the Cambridge IGCSE Marine Science (0697) course: the Earth and the Moon in space.

• The Earth is a planet orbiting the Sun. The Sun is a star. One orbit takes about 365 days, which is one year, and the Earth travels at about 30 km/s.
• The Moon is a natural satellite orbiting the Earth. A satellite is an object that orbits a planet. The Moon is natural, not made by people, and it goes round the Earth about once every 27 days at about 1 km/s.
• Artificial satellites, such as weather satellites and the International Space Station, are built and launched by people. You can see two of them orbiting the Earth in the game.

Why gravity keeps the Moon and the Earth in orbit

Gravity is a force that pulls masses towards each other. The Earth's gravity keeps the Moon in orbit around the Earth, and the Sun's gravity keeps the Earth in orbit around the Sun.

An orbit is a balance. The Moon is always moving sideways, and gravity is always pulling it towards the Earth. Gravity keeps bending its path round, so the Moon keeps falling round the Earth instead of flying away. In the game a blue arrow shows gravity and an orange arrow shows the way the Moon is moving, so you can see the two working together.

• Too slow: gravity bends the path round too sharply and the Moon curves down into the Earth.
• Too fast: gravity can only bend the path a little and the Moon swings far out into space.
• Straight out or straight in: with no sideways motion there is nothing for gravity to bend into a curve, so it falls straight back in.
• Just right, sideways: an orbit.

The six missions

Each mission adds one new idea. First Orbit: choose the launch speed. Aim It: choose the direction too. Gravity Off: a thought experiment where you switch the Earth's gravity off at the right moment. The Moon carries on in a straight line in the direction it was moving, not straight outwards, which shows that gravity is what holds it in orbit. Planet Earth: launch the Earth round the Sun and watch the days count up to a year. Moon on the Move: put the Moon into orbit round the Earth while the Earth travels round the Sun. Stretch: hit beacons on stretched orbits against the clock.

Every mistake shows a short explanation of what went wrong, and quick checks between missions test the key facts. The same pull of gravity also makes the tides, which you meet later in the course.