Case study UK
Greenwich meridian
London
Greenwich connects the convention of zero longitude with the physical relationship between rotation and time. Earth turns through approximately 15 degrees of longitude per hour.
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Location: 51.48°, -0.00°
A prime meridian provides a reference from which longitude is measured east or west. Choosing that reference is a convention. Earth’s rotation supplies the underlying relationship between longitude and local solar time.
Rotate the graticule model while following two meridians. Compare the time at which each faces the Sun, then distinguish local solar time from civil time zones, whose boundaries follow political and practical choices.
Exam-style question
Why is 15° of longitude equal to one hour, and why is the Greenwich meridian not required for that arithmetic?
Teacher hint: Divide 360 degrees by 24 hours to obtain 15 degrees per hour, and separate that geometry from the choice of a zero meridian.
Sources
- Royal Observatory Greenwich