Understanding Longitude: The Meridians That Divide Our Globe
Meridians of longitude are lines that run true north and south, meeting at the earth's poles. They are crucial in geographical and navigational contexts. The following article explores the intricacies of these meridians, their historical significance, and how they are used today to divide our planet into East and West hemispheres.
The Basics of Longitude and Meridians
Longitude refers to the angular distance east or west of the prime meridian. The prime meridian, designated as a line of longitude, passes through the Royal Observatory at Greenwich, London. It is the starting point for measuring meridians east and west. The prime meridian is at zero degrees longitude, and meridians run symmetrically to the east and west from it, up to 180 degrees in either direction. Thus, there are 360 degrees of meridians in total, with both 0 and 180 degrees being common to each hemisphere.
Why Meridians Are Not Parallel to Latitudes
Meridians of longitude are not parallel to each other, unlike lines of latitude. Parallelism is a characteristic specific to the latitudinal lines. Since meridians are all great circles that run north and south, they intersect at the North Pole and the South Pole. The reason for this distinction is that latitudes measure the angle of the equator plane above or below the observer, while longitudes measure angular distance based on time differences. Parallelism is based on the axial tilt of the Earth, which does not apply to longitudinal lines.
The Prime Meridian: A Historical Reference
Historically, the choice of the prime meridian was not static but evolved over time with the development of global navigation. Initially, cities such as Rome, Paris, and Amsterdam were used as references for longitude. Notably, Christopher Columbus used the island of Hierro in the Canary Islands as his reference for longitude. Today, the international standard for the prime meridian is the one that passes through the Royal Observatory at Greenwich, London, also known as the Greenwich Meridian.
The Importance of the Marine Chronometer
The development of the marine chronometer by John Harrison in the 18th century made accurate determination of longitude possible for the first time. Before the marine chronometer, navigation relied on the Great Johannine Table, which utilized the observation of the moon's position relative to Jupiter to infer the time difference. However, this method required reliable land-based telescopic observations and was not as accurate as the marine chronometer, which could keep precise time at sea.
As time progressed, the reliance on the marine chronometer allowed for more accurate and reliable navigation, leading to the modern division of the world into time zones based on meridians of longitude. This method of determining time zones helps in synchronizing global time and is crucial for international trade, aviation, and communication.
Conclusion
In summary, meridians of longitude are a critical component in the global geographical and navigational systems. Their unique characteristic of being great circles and not paralleling each other is essential for accurate measurements. The prime meridian, established by the Royal Observatory in Greenwich, serves as the standard reference. The development of the marine chronometer by John Harrison marked a significant advancement in navigation, making the accurate determination of longitude possible, and furthering the standardization of global time zones.