HistoryExtra Podcast: "Why Greenwich is the Home of Time"

Date: February 4, 2026
Host: Eleanor Evans
Guest: Dr. Emily Ackermans, Curator of Time at Royal Museums Greenwich

Episode Overview

This episode explores why Greenwich, a small site in South East London, became the global reference point for timekeeping. Dr. Emily Ackermans talks with Eleanor Evans about the astronomical, scientific, and social developments at the Royal Observatory in Greenwich, explaining how its work solved navigation’s greatest challenges, gave the world Greenwich Mean Time (GMT), and established the Prime Meridian. The conversation traces developments from the 17th-century quest for longitude to atomic clocks and the daily life within this globally significant site.

Key Discussion Points & Insights

1. The Curator of Time: A Unique Role

• [01:08] Dr. Emily Ackermans describes her position:
  “I look after our fantastic collection of timekeeping objects ... many of these are the objects that have been used over the past 350 years here at the Royal Observatory in Greenwich ... including the famous Harrison experimental sea clocks ... and the massive red ball ... known as the Time Ball.”

2. Why Greenwich? The Historical Context

• [01:58] Greenwich became crucial due to its role in accurate time measurement for astronomy and navigation.
• Human societies always measured time (for harvests, markets, rituals), but accurate time was essential for navigation and astronomy.
• Early timekeeping instruments included sundials, water clocks, and sand timers.

3. Solving the Longitude Problem

The 17th-Century Revolution

• [03:51] Introduction of the pendulum to clockmaking greatly increased accuracy (from minutes per day to seconds).
• The Royal Observatory, established in 1675 by Charles II, aimed to precisely map the stars for navigation.
• [05:17] Problem: Latitude could be found via the sun/star height, but longitude required knowing the time at another reference point.
• Dead reckoning was error-prone; a better system was needed.

John Flamsteed, The First Astronomer Royal

• [09:17] Appointed with the task of mapping the stars to perfect navigation.
• Installed state-of-the-art clocks (by Thomas Tompion), whose 13ft pendulums ran for a year on a single winding.
• Notable Quote [10:57]: "With what the accuracy that they could achieve with the clocks, this was an important development and allowed the subsequent centuries of work to be done here at Greenwich." – Dr. Emily Ackermans

4. The Rise of Greenwich Mean Time (GMT)

• [11:29] GMT’s adoption was a gradual process, emerging as navigators worldwide used star charts and data produced at Greenwich.
• The Observatory’s chronometers became the standards for Royal Navy voyages.
• Over time, shipbuilders and navigators increasingly anchored their work on GMT.

5. The Time Ball and Public Time Signals

• [13:33] The Time Ball, a daily visual time signal for ships on the Thames; dropped at exactly 1pm so mariners could check and adjust their chronometers.
• Similar time balls appeared at ports globally; some were even electrically operated.
• Memorable Moment [14:55]: The Time Ball still drops daily at 1pm, except in extreme wind.

6. Time for the People: Standardization and the Railways

• [18:05] During the 19th century, railways and industrialization demanded standardized time.

• Local times caused confusion; for example, noon at Bristol is 10 minutes after Greenwich.

• The Shepherd's Sympathetic Clock System (invented in the 1850s) sent accurate time from Greenwich via telegraph to railways and businesses.

• The Belleville family physically “sold” accurate time by bringing it from the Observatory to clients in London.

  Notable Quote [21:35]: "That's very entrepreneurial, isn't it? Seeing the gap and then just going for it. Wonderful." – Eleanor Evans

7. The Global Adoption of the Prime Meridian

• [21:54] In 1884, the Washington Conference established the Greenwich Meridian as 0° longitude after much debate.
• Other meridians (Paris, Washington) had been used, but 72% of shipping already used Greenwich.
• The idea of a “neutral” oceanic prime meridian was considered but dismissed for practicality.

8. The Meridian Today & Technological Shifts

• [25:39] The historical Prime Meridian runs through the Observatory courtyard, but due to modern measurement technologies, the “real” 0° longitude is now about 100 meters east.

• [27:02] In the late 20th century, atomic clocks replaced astronomical observations; seconds are now based on cesium atoms, not the Sun’s position.

• UTC (Universal Coordinated Time) is today’s atomic standard, coordinated globally.

  Notable Quote [27:51]: “Greenwich Mean Time is actually no longer measured ... Time is now measured via atomic clocks ... and the time standard is atomic time.” – Dr. Emily Ackermans

9. The Ongoing Story of Time Measurement

• [29:58] Timekeeping is still evolving (development of deep space atomic clocks, potential for a new definition of the second).
• Modern navigation—including space exploration—carries the legacy of Flamsteed and the work at Greenwich.

10. Objects That Tell the Story

• [31:11] Highlights include the Harrison sea clocks (the first marine chronometers); an early 19th-century star alarm clock that notified its maker whenever an important star was due to transit.
• The Observatory’s life included families, children, assistants—all contributing to its social and scientific legacy.

Notable Quotes & Memorable Moments

• On the significance of GMT:
  “If you break it down into Greenwich, Mean and Time, you just learn so much. You learn about time measurement, you learn about why is it mean time, you learn about why is it in Greenwich.” — Dr. Emily Ackermans [30:36]

• On the Prime Meridian selection:
  “Eventually, Greenwich is selected to represent zero degrees longitude ... it was the practical solution to use Greenwich.” — Dr. Emily Ackermans [24:36]

• On the social history inside Flamsteed House:
  “...when John Flamsteed and his wife Margaret had no children, but later astronomer royals had bigger families and they extend the building ... some of the children did like watercolor paintings of the observatory.” — Dr. Emily Ackermans [33:31]

Timestamps for Key Segments

• 01:08 – Dr. Emily Ackermans on her role and the Observatory’s collections
• 03:51 – Development of the pendulum clock and Observatory’s foundation
• 05:17 – The Problem of Longitude explained
• 09:17 – John Flamsteed’s early work and clocks by Tompion
• 11:29 – Rise and adoption of Greenwich Mean Time
• 13:33 – The Time Ball and its global influence
• 18:05 – Standardization via railways; the Shepherd Clock System
• 21:54 – The 1884 Washington Conference and Prime Meridian adoption
• 25:39 – The historic Meridian and its modern representation
• 27:02 – Shift from mean solar time to atomic time and UTC
• 31:11 – Harrison sea clocks and the star alarm clock
• 33:31 – Family life and social stories at the Observatory

Final Takeaways

Greenwich holds its place as the "home of time" due to centuries of innovation, international cooperation, and scientific advancement. From pendulum clocks to deep-space atomic clocks, Greenwich’s story is one of continuous discovery and adaptation to new frontiers in measuring and organizing our experience of time.

Dr. Emily Ackermans sums it up [30:36]:
"If you break it down into Greenwich, Mean, and Time, you just learn so much ... all tied up into the history of the Royal Observatory and the history of navigation and the development of accurate timekeeping."