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

4.1 - Understand the difference between sidereal and synodic (solar) days

4.2 - Understand the role of the Sun in determining Apparent Solar Time (AST)

4.3 - Understand the role of the Mean Sun in determining Mean Solar Time (MST) and Local Mean Time (LMT)

4.4 - Be able to use: the Equation of Time = Apparent Solar Time (AST) – Mean Solar Time (MST)

4.5 - Understand the annual variation of the Equation of Time

4.6 - Understand the causes of the annual variation of the Equation of Time

4.7 - Understand how to determine the time of local noon using shadows, including use of a shadow stick

4.8 - Understand the structure and use of sundials

4.11 - Understand the annual variation in times of sunrise and sunset

4.12 - Understand the astronomical significance of equinoxes and solstices

4.13 - Understand the variation in the Sun’s apparent motion during the year, particularly at the equinoxes and solstices

4.14 - Understand the relationship between sidereal and synodic (solar) time

4.15 - Understand the difference in local time for observers at different longitudes

4.16 - Understand the use of time zones

4.17 - Be able to use data related to time zones

4.18 - Know that mean time at any point along the Prime Meridian is defined as Greenwich Mean Time (GMT), which is the same as Universal Time (UT)

4.19 - Be able to use shadow-stick data and the Equation of Time to determine longitude

4.20 - Understand the principles of astronomical methods for the determination of longitude, including the lunar distance method

4.21 - Understand the principle of the horological method for the determination of longitude (Harrison’s marine chronometer) (knowledge of internal working of chronometers not required)


Human civilisation is dependent on understanding time.

Our agriculture and economy depend on knowing the time of day and what season of the year it is.

Finding out the time would be quite easy were it not for the tilt and orbit of the Earth.

Society has invented a mean (average) Sun to tell the time and has created time zones around the world.
Time can be a complicated business, so let’s not waste any of it.

At the end of this section take the mini quiz to test yourself.