calculated = worked out
I maginary = not real
tricky = difficult
navigate = sail/steer
pinpoint = find the exact position of
brilliant = very intelligent
divides = cuts into parts
boasts = has something that it is proud of
All time zones in the world are calculated from the prime meridian in Greenwich.
The prime meridian is an imaginary line that divides the globe into two hemispheres.
The Royal Observatory was set up to solve a tricky problem; sailors needed to know what the exact time was to navigate their way around the world and pinpoint where they were.
Brilliant scientists came up with the idea of the prime meridian.
The Royal Observatory also boasts London’s only planetarium.