What is a Meridian?

A meridian is an imaginary line that runs from the North Pole to the South Pole on the Earth’s surface. Meridians are used to measure longitude, which is the angular distance east or west from the Prime Meridian.

The Prime Meridian, located at 0° longitude in Greenwich, England, is the starting point for measuring longitude. Meridians are spaced 1 degree apart, and there are 360 meridians around the Earth.

Each meridian corresponds to a specific time zone, helping us keep track of local times around the globe.

What is the Terminator Line?

The terminator line, also called the twilight zone or day-night boundary, is the dividing line on Earth that separates the daylight side from the nighttime side.

As Earth rotates, the terminator moves westward, causing the cycle of day and night across different regions.

This line is not a sharp boundary but a gradual transition zone where sunrise and sunset occur.

How Meridians and the Terminator Affect Time and Daylight

Because Earth rotates 360 degrees in 24 hours, every 15 degrees of longitude corresponds to a one-hour difference in solar time.

Meridians help define these time zones, while the terminator determines which parts of Earth are in daylight or darkness at any given moment.

Understanding these concepts is essential for navigation, global communication, and timekeeping.

Example: Observing the Terminator from Space

Astronauts aboard the International Space Station (ISS) can witness the terminator moving rapidly across Earth’s surface, causing the sky to shift from night to day within minutes.

This beautiful transition demonstrates how the terminator line shapes the cycle of day and night we experience.

Quick Facts

• There are 360 meridians, one for each degree of longitude.
• The Prime Meridian at Greenwich is the reference for all other longitudes.
• The terminator line is always moving due to Earth’s rotation.
• The terminator causes dawn and dusk periods.

Conclusion

Meridians and the terminator line are fundamental geographic concepts that explain how we measure longitude and experience the cycle of day and night.By understanding these, you gain a clearer picture of how Earth’s rotation affects time zones and daylight across the planet.