Question

What and where is the prime meridian? How was the location originally selected? Describe the meridian that is opposite the prime meridian on Earth's surface.

Short answer

The prime meridian is the line of 0 degrees longitude, running through the Royal Observatory in Greenwich, London. Its location was chosen in 1884 due to its widespread use on sea charts. The meridian opposite the prime meridian is called the antimeridian and forms one side of the International Date Line.

Step-by-step solution

Explain the Prime Meridian

The prime meridian is the line of 0 degrees longitude, the starting point for measuring distance both east and west around the Earth. It runs from the North Pole to the South Pole through the Old Royal Observatory in Greenwich, London, United Kingdom.

Discuss its original selection

The location of the prime meridian was decided at the International Meridian Conference in 1884. Delegates from 26 countries met in Washington D.C., USA and voted to accept the Royal Observatory in Greenwich, London, UK as the prime meridian primarily due to its popularity. By that time, 72% of the world's sea charts were already based on it.

Describe the opposite meridian

The meridian that is opposite the prime meridian (meaning it is 180 degrees away from the prime meridian) is called the antimeridian. This line runs through the Pacific Ocean and forms one side of the International Date Line, which is used to adjust calendar dates as one travels east or west across it.

Key concepts

Longitude

The concept of longitude is critical in geography, navigation, and Earth sciences. It refers to the angular measurement used to describe a point's location east or west of the Prime Meridian. Longitude lines, also known as meridians, run vertically between the North and South Poles. Think of these lines as slices of an orange, equally dividing the planet into segments.

When measuring longitude, the Prime Meridian is assigned the value of 0 degrees. From there, longitude can range up to 180 degrees east or west. For example, New York City has a longitude of approximately 74 degrees west.

Importance of Longitude

Longitude is incredibly useful in global positioning. It allows us to pinpoint exact locations on Earth and aids in international travel and the synchronization of time zones across the world. As we rely increasingly on satellite navigation, understanding longitude and its role in GPS technology is more important than ever.

International Meridian Conference

Before the International Meridian Conference of 1884, there was no uniform starting point for longitude, leading to confusion and inefficiency, especially in navigation and mapmaking. This conference, held in Washington D.C., was an assembly of representatives from 26 countries to settle on a common zero point for longitude.

Decision and Impact

Attendees voted to adopt the meridian passing through the Royal Observatory in Greenwich as the official Prime Meridian. This decision was based on its widespread usage at the time and its practical location for maritime navigation. The outcome standardized maps and charts and effectively facilitated international timekeeping and travel. It was a significant step toward global coordination and reflects the consensus-driven nature of international agreements.

Antimeridian

The antimeridian is the counterpart to the Prime Meridian, situated at exactly 180 degrees longitude on the opposite side of the Earth. This imaginary line is not as universally recognized as the Prime Meridian due to its passage through the remote expanses of the Pacific Ocean. However, it serves a vital role in timekeeping.

International Date Line and Time Zones

The International Date Line follows the antimeridian closely but deviates in certain areas to accommodate political and territorial boundaries. It is the line where the date changes by one day when crossing from one side to the other. This system maintains consistent calendar days within the same region and avoids confusion in dating across neighboring areas.