Prime Meridian has a fascinating history on its own, definitely worth being taken in consideration. The Greenwich Meridian is used to separate east from west in the same way that the Equator separates north from the south. In 1884 in Washington D.C. delegates gathered for an international convention to determine where the 0° of longitude should be. The majority of shipping companies at that time were already using British charts based on the British Meridian and it seemed agreeable for most of the nations represented to move towards a decision of adopting the same one as a Prime Meridian (longitude zero). The delegates recommended also the definition of a new global time zone system based on the Greenwich meridian. The alignments were checked with the help of two telescopes used together to determine the collimation (sight-line) of the Airy Transit Circle’s telescope and to ensure it is aligned correctly on the Meridian. In a separate building there is a huge telescope that defines the Prime Meridian even today. The telescope was commissioned by George Biddell Airy, seventh Astronomer Royal. History tells us that Astronomers worked in pairs on the Airy Transit Circle: one looked through the eyepiece while the other observed the microscope readings on the stone pier. The other two astronomers that worked on the meridian line were Edmond Halley and James Bradley. Halley’s Meridian line was defined by measuring the height of stars above the horizon; then their passage (or ‘transit’) was timed over the meridian mark by crosshairs in his telescope with an accurate pendulum clock. One of the most important observations was the Sun at solar noon. Bradley’s Meridian line was defined by the third Astronomer Royal who observed with improved accuracy while using the telescope. Time was measured by using distant stars ⭐️ in an attempt to be more accurate having in mind the unequal length of solar days. It is said that Astronomers’ clocks run slightly faster than normal clocks to show sidereal (star) time. Time has already began to play an important role with timekeeping and clocks being introduced in homes 🏡 and trades.