Activity schedules, time entries in logbooks and contact confirmations usually refer to UTC (Coordinated Universal Time). What is the location of the meridian from which this time is measured?

Coordinated Universal Time (UTC) is the standard time used across the world. It is highly important for amateur radio operators to use UTC to log contacts consistently and avoid timezone confusion. UTC is based on the Prime Meridian, which is defined as 0 degrees longitude. This meridian passes directly through the Royal Observatory in Greenwich, London, United Kingdom, which is why UTC is historically referred to as Greenwich Mean Time (GMT). While other cities like Geneva or Boulder host important telecommunications or timekeeping organizations (like the ITU or NIST), the Prime Meridian itself is geographically fixed at Greenwich.