Greenwich, England: Home of the Prime Meridian & GMT

Why Greenwich Is the Center of World Time & Navigation

📍 The Prime Meridian (0° Longitude)

Defined at the Royal Observatory, Greenwich (1851, Sir George Airy). Adopted as **global standard at 1884 International Meridian Conference** (22/25 nations voted yes). Divides Eastern/Western Hemispheres.

⏰ Greenwich Mean Time (GMT)

• Mean solar time at Royal Observatory.
• World's **time standard (1884–1972)** – replaced by **Coordinated Universal Time (UTC)**, atomic-based but kept within 0.9s of GMT.
• Still UK civil time (winter); **British Summer Time (BST = GMT+1)** in summer.

🧭 Navigation Revolution

**Longitude Problem:** Latitude easy (sun angle). Longitude required accurate time comparison: Local noon vs. GMT.

• John Harrison's Marine Chronometers (H1–H4, 1730–1760) – solved it.
• Ships carried GMT chronometers → calculate longitude = (Local Time - GMT) × 15°/hr.
• Greenwich = reference for all nautical almanacs, charts, ephemerides.

🌍 Global Synchronization

• Railways: Adopted GMT (1840s) – ended "local mean time" chaos (Bristol 10 min behind London).
• Telegraph: Time signals distributed globally (1852 onward).
• Time Zones: Proposed by Sandford Fleming (1876), based on Greenwich – adopted 1884.

🏛️ Visit Today

• Royal Observatory Greenwich (UNESCO Maritime Greenwich) – stand on Meridian Line, see H4, planetarium.
• National Maritime Museum – Harrison's clocks, naval history.
• Cutty Sark – last tea clipper.
• Queen's House – Inigo Jones architecture.

Greenwich gave the world a shared clock and a common grid – the invisible infrastructure of globalization.