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Topic 3: The Earth-Moon-Sun system

3 dot points across 3 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

What causes solar and lunar eclipses, and why do they not happen every month?

The causes and appearance of solar eclipses (partial, total, annular) and lunar eclipses (partial, total), including the terms first, second, third and fourth umbral contact.
A focused answer to Edexcel GCSE Astronomy statements 3.8 to 3.10, covering the causes of solar and lunar eclipses, the appearance of the Sun during partial, total and annular solar eclipses and of the Moon during partial and total lunar eclipses, the umbral contact terms, and why eclipses do not occur every month.
10 min answer →

How big are the Earth, Moon and Sun, how far apart are they, and how did ancient astronomers measure this?

The relative sizes and distances of the Earth, Moon and Sun, the Sun's mean diameter, and how Eratosthenes and Aristarchus determined the sizes and distances from observations.
A focused answer to Edexcel GCSE Astronomy statements 3.1 to 3.4, covering the relative sizes and distances of the Earth, Moon and Sun, the Sun's mean diameter of 1.4 x 10^6 km, and how Eratosthenes measured the size of the Earth and Aristarchus estimated the sizes of and distances to the Moon and Sun.
10 min answer →

What causes the tides, and how does the slow wobble of the Earth's axis change the sky over centuries?

The relative effects of the Sun and Moon in producing spring and neap tides, and the precession of the Earth's axis, its effects on the sky and its use in archaeoastronomy.
A focused answer to Edexcel GCSE Astronomy statements 3.5 to 3.7, covering how the gravitational pull of the Moon and Sun produces high and low tides and spring and neap tides, and how the slow precession of the Earth's axis changes the position of the celestial pole and the equinoxes, with its use in archaeoastronomy.
9 min answer →