Final answer:
The line passing through the Royal Observatory, Greenwich, England, is known as the Greenwich Meridian or Prime Meridian, which is the zero point of longitude used to measure distances east and west on the Earth.
Step-by-step explanation:
The line that passes through the Royal Observatory, Greenwich, England is known as the Greenwich Meridian or the Prime Meridian. This line represents the internationally agreed-upon zero point of longitude, a starting point for measuring distance both east and west around the Earth's surface. Every place on Earth is measured in terms of its distance east or west from this line, with longitudes ranging from 0° at the Prime Meridian to 180° at the International Date Line.
Why was Greenwich chosen as the zero point of longitude? Historically, every country wanted the 0° longitude to pass through its capital, but Greenwich was chosen because of its geographical location, situated conveniently between continental Europe and the United States. Moreover, the Royal Observatory in Greenwich was a significant site in the development of methods to measure longitude at sea, which was crucial for navigational purposes during the age of exploration and trade.
When visiting the Royal Observatory at Greenwich, tourists can physically stand on the meridian line, an experience that symbolizes standing at the very starting point of the world's system of longitude.