Everything Everywhere Daily: Episode Summary - "The Prime Meridian"

Release Date: February 5, 2025

Host: Gary Arndt
Producer: Charles Daniel
Associate Producers: Austin Oakton and Cameron Keefer
Executive Producer: Charles Daniel

Introduction to the Prime Meridian

In this enlightening episode of Everything Everywhere Daily, host Gary Arndt delves into the intriguing history and significance of the Prime Meridian. Located at the Royal Greenwich Observatory in East London, this invisible line extends from the North Pole to the South Pole, serving as the reference point for all other lines of longitude worldwide. Arndt sets the stage by highlighting the seemingly arbitrary nature of its designation as the world's primary longitudinal reference.

Gary Arndt [00:00]: "Located in East London is the Royal Greenwich Observatory. Passing directly through the observatory is an imaginary line that extends from the North Pole to the South Pole... What makes it even more remarkable is that there's no objective reason for this particular line to be so important."

The Geographic Coordinate System

Arndt provides a comprehensive overview of the geographic coordinate system, emphasizing its two main components: lines of latitude and lines of longitude.

Lines of Latitude

Latitude lines, or parallels, run horizontally around the Earth, measuring distances north or south of the equator. They are fixed at specific degrees:

• Equator: 0°
• Tropic of Cancer: 23.5°N
• Tropic of Capricorn: 23.5°S
• Arctic Circle: 66.5°N
• Antarctic Circle: 66.5°S

Each degree of latitude consistently measures approximately 69 miles (111 kilometers), shrinking to a point at the poles.

Lines of Longitude

Longitude lines, or meridians, run vertically from pole to pole. Unlike latitude, their distance varies depending on the latitude, with the widest separation at the equator (about 69.172 miles or 111.321 kilometers). Arndt underscores the challenges early navigators faced in determining longitude, which was pivotal for accurate navigation and preventing shipwrecks.

Gary Arndt [00:47]: "Lines of longitude run north, south from pole to pole, unlike lines of latitude, which never touch... Every line of longitude meets at the poles."

Historical Challenges in Determining Longitude

Determining precise longitude was a significant hurdle in maritime navigation. While latitude could be gauged using tools like the sextant and celestial bodies, longitude required accurate timekeeping. This conundrum led to numerous shipwrecks due to navigational errors.

The breakthrough came with John Harrison, an 18th-century English clockmaker, who developed a highly accurate marine chronometer. By comparing the ship's local noon with the time on the chronometer set to a known reference point, navigators could calculate their longitude accurately.

Gary Arndt [10:34]: "An 18th-century English clockmaker by the name of John Harrison developed a highly accurate timepiece that could work on sailing ships... The difference in time would then determine what line of longitude you were at."

Development and Adoption of the Greenwich Prime Meridian

Despite advancements in longitude determination, selecting a universally accepted Prime Meridian remained elusive. Various civilizations and nations proposed their own reference lines:

• Ancient Greece: Eratosthenes and Hipparchus proposed early longitude systems.
• Greco-Roman Era: Ptolemy established a reference at the Fortunate Islands (Canary Islands).
• Middle Ages Europe: Jerusalem and Rome were commonly used.

During the Age of Discovery, nations like Spain, France, and Britain each maintained their own prime meridians based on national observatories—Madrid, Paris, and Greenwich respectively.

As global trade expanded, the need for standardization became apparent. The International Geodetic Association convened in 1883 in Rome to address this issue, ultimately recommending Greenwich due to its superior astronomical data and navigational prominence.

In 1884, the International Meridian Conference in Washington D.C. formalized Greenwich as the world's Prime Meridian, establishing Greenwich Mean Time (GMT) as the global time standard.

Gary Arndt [22:15]: "In 1884, the International Meridian Conference was held in Washington D.C. where 22 of 25 countries voted to adopt the Greenwich Meridian as the Prime Meridian and use Greenwich Mean Time as the World Standard Time."

Modern Prime Meridian and GPS

While the historical Greenwich Prime Meridian remains a cultural and navigational landmark, modern technology has introduced a more precise system. The Global Positioning System (GPS) defines the Prime Meridian based on the International Terrestrial Reference Frame (ITRF), which utilizes satellite data to measure the Earth's shape and rotation from its center of mass.

This geodetic Prime Meridian is situated approximately 102 meters (334 feet) east of the historic Greenwich line, reflecting the advancements in measurement accuracy.

Gary Arndt [28:45]: "The GPS defined Prime Meridian is based on the International Terrestrial Reference Frame... As a result, the modern geodetic Prime Meridian used in GPS is located about 102 meters, or 334ft, east of the historic Greenwich Line."

Prime Meridian in Other Locations

Beyond Greenwich, the Prime Meridian passes through several other countries, including France, Spain, Algeria, Mali, and Burkina Faso. Notably, near Accra, Ghana, drivers can witness the marker of the Prime Meridian in action.

Arndt also introduces the concept of Null Island, a fictional point at 0° latitude and 0° longitude in the Atlantic Ocean, often used in geospatial contexts to represent missing or erroneous data.

Gary Arndt [31:20]: "If you go further south of Ghana into the ocean, you will eventually reach a point in the open water which is known to geographers as Null Island. This isn't an actual island. It's simply where the Prime Meridian crosses the equator."

Prime Meridians of Other Celestial Bodies

Expanding the discussion beyond Earth, Arndt explores how prime meridians are established on other celestial bodies. While often arbitrary, some natural features can serve as references:

• Mars: Defined by the longitude passing through the crater Ariel, establishing a standardized Martian coordinate system.
• The Moon: Possesses a natural prime meridian due to tidal locking with Earth. The meridian runs through the point closest to Earth, providing a consistent reference for lunar mapping.

Gary Arndt [36:10]: "On the Moon, its Prime Meridian runs right down the center of the side that you can see the next time you look at a map online or determine a route somewhere on your smartphone... because the Moon is tidally locked to the Earth."

Conclusion

Gary Arndt wraps up the episode by reflecting on the arbitrary yet impactful decision to designate the Greenwich Prime Meridian. This choice has facilitated global navigation, standardization of time, and international cooperation. The episode underscores the blend of human ingenuity and consensus in shaping the frameworks that govern our understanding of the world.

Gary Arndt [41:50]: "Take a moment and think that it's all possible because of an arbitrary decision to place the Prime Meridian at an observatory in East London."

Listener Interaction:

The episode concludes with a light-hearted interaction, where Gary addresses a listener's review debating the controversial topic of pineapple on pizza—highlighting the podcast's ability to make diverse subjects engaging.

Listener Nugget [44:00]: "Hi Gary, I love listening to this podcast... do you like pineapple on pizza?"
Gary Arndt [44:30]: "I hate to break it to you, but pineapple doesn't belong anywhere near pizza. The one true pizza topping that every pizzeria should have is, of course, anchovies."

Key Takeaways:

• The Prime Meridian at Greenwich serves as the foundational reference for global longitude.
• Accurate determination of longitude was historically challenging but revolutionized by precise timekeeping.
• International consensus in 1884 established Greenwich as the global standard, later refined by GPS technology.
• Prime meridians on other planets and celestial bodies can be either arbitrary or naturally defined.
• The episode blends deep historical insights with relatable anecdotes, making complex geographic concepts accessible and engaging.

For more fascinating stories about people, places, and things from around the world and throughout history, tune into Everything Everywhere Daily with Gary Arndt.