Moons, Asteroids and Watching the Sky: Concept Map

Concept Map

Organise the vocabulary, quantities and relationships into a connected model.

This extension applies that lens specifically to Moons, Asteroids and Watching the Sky.

The solar system holds far more than the Sun and eight planets.

• A moon is a natural object that orbits a planet. Earth has one; Jupiter and Saturn each have dozens. Note the difference carefully: planets orbit the Sun, moons orbit planets.
• Dwarf planets are round objects orbiting the Sun that are too small, and share their space with too many similar objects, to count as full planets. Pluto and Ceres are examples.
• Asteroids are rocky objects, most of them circling the Sun in a wide band between Mars and Jupiter called the asteroid belt.
• Comets are balls of ice and dust on long orbits. Near the Sun the ice turns to gas and the comet grows a glowing tail that always points away from the Sun.
• Meteors — "shooting stars" — are small pieces of rock burning up brightly as they rush into Earth's air. They are not stars at all.

How we know all this — and South Africa's part in it.

Most of this knowledge comes from telescopes, and some of the world's best are on our soil. At Sutherland in the Northern Cape stands SALT, the Southern African Large Telescope — the largest single optical telescope in the southern hemisphere. Further into the Karoo, the MeerKAT radio telescope listens to the sky, and it forms part of the international Square Kilometre Array project.

Why the Karoo? A good telescope site needs dark, dry, still, cloud-free skies far from city lights, and the Karoo delivers all four better than almost anywhere on Earth. The glow of streetlights over a city — light pollution — washes faint objects out of the sky entirely.

You do not need a telescope to start. On a clear night far from town, the Milky Way is visible with your eyes alone.