päämeridiaaniin

Päämeridiaaniin, also known as the prime meridian, is an imaginary line of longitude that marks 0 degrees longitude. It is the reference point from which all other lines of longitude are measured, both east and west. The prime meridian runs through Greenwich, London, England, and is therefore often referred to as the Greenwich Meridian.

Historically, various locations have been proposed as the prime meridian. However, in 1884, an international conference in Washington D.C. established the Greenwich Meridian as the global standard. This decision was largely based on the fact that a significant portion of the world's shipping and astronomical charts already used Greenwich as their reference.

The prime meridian plays a crucial role in navigation and timekeeping. It divides the Earth into the Eastern Hemisphere and the Western Hemisphere. Time zones are also calculated relative to the prime meridian. Coordinated Universal Time (UTC) is the primary time standard by which the world regulates clocks and time. UTC is effectively the successor to Greenwich Mean Time (GMT).

The concept of a prime meridian is fundamental to understanding the Earth's geographical grid system. Without a universally agreed-upon reference line, mapping and global coordination would be significantly more complex.