Meridian (geography)

A meridian is a line on Earth.

It runs from the North Pole to the South Pole. These lines help us find our way. They also help us tell time.

Long ago, many lands used their own lines. This made it hard to travel. Trains and ships needed one plan.

In 1884, many countries met to help. They chose one main line. This line goes through Greenwich, England.

Now, we use this line to set the time. It helps the whole world stay on track.

A meridian is an imaginary line on Earth.

These lines run from the North Pole to the South Pole. They help us find locations. They also help us track time. We use them to measure longitude. Longitude is the angle east or west of a main line. This main line is called the prime meridian.

Long ago, it was hard to travel. Many places used their own lines. This made it difficult to coordinate trains. In 1884, leaders met in Washington, D.C. Twenty-six countries went to the meeting. They wanted one standard system. They chose a line that passes through Greenwich, England.

This line is at zero degrees. It divides the world into two parts. One part is the Eastern Hemisphere. The other is the Western Hemisphere. The line on the far side of Earth is called the antimeridian. It sits at 180 degrees.

Meridians also help us with the Sun. When the Sun is at its highest point, it passes a meridian. This is called meridian passage. People use this to find their latitude. Latitude is how far north or south you are from the Equator.

A meridian is a special line used to map our world.

These lines connect the North Pole to the South Pole. They help us measure longitude. Longitude is the angle measured east or west from a starting line. This starting line is called the prime meridian. On a map, these lines look like they cross latitude lines at right angles. If we imagine Earth as a perfect sphere, a meridian is a great semicircle. If the Earth is an ellipsoid shape, it is half of a great ellipse.

Understanding meridians helps us know exactly where we are. You can find your position using both longitude and latitude. Latitude tells you how far north or south you are from the Equator. The prime meridian sits at zero degrees longitude. It divides the Earth into two halves. The side to the east is the Eastern Hemisphere. The side to the west is the Western Hemisphere. On the exact opposite side of the world is the antimeridian. This line is at 180 degrees longitude.

Finding a single starting line was once a very hard job. In the early modern era, many countries used their own meridians. This caused confusion for travelers and traders. It even made it difficult to run railway services. Each town often used its own local time. To fix this, leaders held the International Meridian Conference in 1884. Twenty-six countries met in Washington, D.C. to vote on a single standard. They chose the meridian that passes through Greenwich, England. This became the 0° line for the whole world.

Meridians also help us track the movement of the Sun. When a star or the Sun reaches its highest point, it is called meridian passage. This happens when the object crosses the observer's meridian. Navigators used this moment to calculate their latitude. They could use the Sun's height and its declination to find their way. The word meridian actually comes from the Latin word for "midday." This is because the Sun passes through a meridian at solar noon. This is the middle point between sunrise and sunset. This is also where we get the terms a.m. and p.m.

There are different ways to look at these lines. A true meridian goes from pole to pole through an observer. A magnetic meridian connects the magnetic north and south poles. A compass needle will point parallel to the magnetic meridian. The difference between the true and magnetic lines is called magnetic declination. This is a very important fact for people using compasses to navigate. Today, we use the WGS84 system for our positions. This system moved the geodetic prime meridian 102.478 meters east of the old astronomic spot at Greenwich. You can now find this exact spot using a GPS receiver.

A meridian is a coordinate line used to measure longitude on Earth. Longitude is the angle measured in degrees east or west from a starting point. This starting point is known as the prime meridian.

While latitude measures how far north or south a point is from the Equator, meridians define the east-west position. If we assume the Earth is a perfect sphere, a meridian is a great semicircle. However, Earth is actually a spheroid or an ellipsoid. In this model, a meridian is half of a north-south great ellipse.

Meridians function as part of a global grid system. On certain maps, such as the Mercator or Gall-Peters projections, every meridian is perpendicular to all circles of latitude. This means they cross at right angles. The prime meridian is set at 0° longitude. It divides the planet into two halves. The area to the east is the Eastern Hemisphere. The area to the west is the Western Hemisphere. On the opposite side of the Earth, the antimeridian sits at 180° longitude. This line is located near the International Date Line.

The term meridian has interesting roots in history. It comes from the Latin word *meridies*, which means "midday." This name refers to the subsolar point. This is the point where the Sun passes through a given meridian at solar noon. Solar noon occurs midway between sunrise and sunset. This same Latin root gives us the terms a.m. and p.m. These terms help us tell time using a 12-hour clock. They stand for *ante meridiem* and *post meridiem*.

Finding a single, universal meridian was a major historical challenge. The first prime meridian was set by Eratosthenes in 200 BCE. However, early measurements faced problems because latitude was hard to measure. By the early modern era, different countries used their own preferred meridians. This lack of consistency made it difficult to record local times and coordinates. It even caused trouble for railway services. Each town often had its own time zone, making coordination very hard. Two locations, Paris and Greenwich, were most commonly used as reference points.

To solve these problems, nations met for the International Meridian Conference in 1884. This meeting took place in Washington, D.C. Twenty-six countries attended the conference to vote on a single standard. They wanted to support a growing international economy. A standard meridian would make worldwide travel and international trading much easier. The conference decided there would be only one prime meridian. It would pass through Greenwich, England, at 0°. They also established a universal day that begins at mean midnight. They decided that east would be represented by plus values and west by minus values up to 180°.

There are different types of meridians used in science and navigation. A true meridian is a chord that goes from pole to pole through an observer. In contrast, a magnetic meridian connects the magnetic north and south poles. A compass needle will point parallel to the magnetic meridian. The difference between the true meridian and the magnetic meridian is called magnetic declination. Navigators must understand this angle to calibrate their compasses correctly. Henry D. Thoreau used these distinctions to account for variations in his own compass.

Meridians are also essential for tracking celestial objects. A meridian passage occurs when a star or the Sun reaches its highest point. This happens when the object crosses the observer's meridian. Navigators used the Sun's altitude during this passage to calculate their latitude. They used a specific formula involving the Sun's declination and its noon altitude. Today, we use the World Geodetic System 84, or WGS84, for positioning. This system moved the geodetic prime meridian 102.478 meters east of the old astronomic position at Greenwich. You can now locate this precise point using a GPS receiver.