Longitude is a geographical coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement expressed in degrees, usually ranging from 0° at the Prime Meridian in Greenwich, England, to +180° eastward and −180° westward. Unlike latitude, which has the equator as a natural starting position, there's no absolute starting position for longitude. Thus, the Prime Meridian at Greenwich, England has been established as the conventional zero-point. This coordinate is essential for locational and navigational purposes, forming the basis for time zones worldwide.

1. The city of Sydney, Australia, is approximately 151 degrees East longitude, meaning it is positioned 151 degrees east from the prime meridian at Greenwich, England. 2. New York City's location is approximately 74 degrees West longitude, so it is located 74 degrees west from the Greenwich meridian. 3. Buenos Aires, Argentina, is positioned approximately at 58 degrees West longitude, denoting its geographical distance westwards from the prime meridian in Greenwich, England. 4. Tokyo, Japan's coordinates show it is approximately 139 degrees East longitude, meaning it lies 139 degrees to the east from the meridian established at Greenwich. 5. Cairo, Egypt, is located approximately at 31 degrees East longitude, depicting its location 31 degrees east of the Greenwich meridian.

Did you know that the concept of longitude, which is essentially the distance in degrees east or west of the meridian at Greenwich, England, played a crucial role in navigating and mapping the world? The idea of longitude was substantially less understood in comparison to latitude. While the latter could be determined relatively easily through celestial observations, determining an accurate longitudinal position was far more complex. These longitudinal compass points eventually became the foundation for today’s GPS satellites. In the 18th Century, John Harrison, a British clockmaker, played a major role by inventing a marine chronometer, a highly precise clock, that solved the problem of calculating longitude while at sea. Interestingly, the Prime Meridian (0-degree longitude) was legally established by Sir George Airy in 1851 at the Royal Observatory in Greenwich, England. This imaginary north-south line is marked by a thick, illuminated strip within the observatory’s courtyard, and also by a green laser beam that shines northward across the London night sky. What makes this even more interesting is that until the International Meridian Conference held in Washington D.C. in 1884, there was no standardized system of longitude. The Greenwich Meridian was eventually chosen as the Prime Meridian of the world, making it the center of the world’s time zone system. So, think about the fact that half the world is always in 'today' and the other half in 'tomorrow' due to these longitudinal lines – isn't that fascinating?