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Topic 4: Time and the Earth-Moon-Sun cycles

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

Why does a sundial disagree with a clock, and by how much through the year?

Apparent and mean solar time, the Equation of Time and its annual variation, and the use of shadows, shadow sticks and sundials to find local noon and time.
A focused answer to Edexcel GCSE Astronomy statements 4.2 to 4.8, covering Apparent Solar Time and Mean Solar Time, the Equation of Time (AST minus MST) and its causes and annual variation, and the use of shadows, shadow sticks and sundials to determine local noon and time.
10 min answer →

Why is a solar day longer than a sidereal day, and what drives the cycle of the Moon's phases?

The difference between sidereal and synodic (solar) days and months, the lunar phase cycle, and the astronomical significance of equinoxes and solstices.
A focused answer to Edexcel GCSE Astronomy statements 4.1, 4.9 to 4.14, covering the difference between sidereal and synodic (solar) days and months, the cause of the lunar phase cycle, and the astronomical significance of the equinoxes and solstices and the Sun's changing apparent path.
9 min answer →

Why do different places keep different clock times, and how did sailors find their longitude?

Local time and longitude, time zones, GMT and UT, and the astronomical and horological methods of determining longitude, including Harrison's marine chronometer.
A focused answer to Edexcel GCSE Astronomy statements 4.15 to 4.21, covering how local time depends on longitude, the use of time zones, GMT and Universal Time, and the astronomical (lunar distance) and horological (Harrison's marine chronometer) methods of determining longitude.
9 min answer →