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You have seen the Moon change shape. Why does it? Where did the day, the month and the year come from?

This is Chapter 11, Keeping Time with the Skies.

What you will learn

• A day — the Earth spins once.
• A shadow clock — a stick measures a day.
• A month — the Moon's phases.
• A year — the seasons come round.
• A leftover — Moon months and years do not fit.
• Leap years — a spare day in most fourth years.
• Calendars — solar (Sun), lunar (Moon) and luni-solar (both).
• Finding the Moon — where to look at sunset and sunrise.
• Satellites — human-made objects that orbit (go round) the Earth.

Need a quick recap?

• Something that repeats evenly (Time and Motion) — a clock counts repeats.
• Two motions (Earth, Moon and the Sun) — spinning and going round.
• The Moon (Beyond Earth) — it shines by sunlight.

Stay safe

Never look at the Sun, even through glasses or a lens. Watch its shadow instead.