In a globalized world, a single, unambiguous time standard is essential. That standard is Coordinated Universal Time, or UTC. It is the time standard by which the world regulates clocks and time. For developers, pilots, financiers, and data scientists, UTC is not just a reference; it is the language of time itself.

The Predecessor: Why GMT is No Longer the Time Standard

Greenwich Mean Time (GMT) was the original global time standard, based on the mean solar time at the Royal Observatory in Greenwich, London. However, it was an astronomical standard, tied to the slightly irregular rotation of the Earth. UTC, established in 1960, is a more precise atomic standard. While GMT is now technically just a time zone used in some parts of the world, the term is often used colloquially to refer to UTC.

The Science of UTC: Atomic Time (TAI) vs. Astronomical Time

UTC is a brilliant compromise. It is based on International Atomic Time (TAI), an incredibly precise time scale produced by hundreds of atomic clocks worldwide. However, because the Earth's rotation is slowly decelerating, TAI gradually drifts apart from time based on the Earth's position (UT1). To keep the two in sync, "leap seconds" are occasionally added to UTC. This process is complex and controversial, as detailed in our guide to The Time Drift.

UTC in Practice: Essential for APIs, Logging, and Finance

In any system that operates across time zones, using local time is a recipe for disaster. Storing all timestamps in UTC is the only way to ensure data integrity.

• APIs & Databases: Storing times in UTC (often as a Unix timestamp) ensures that all server-side logic is consistent, regardless of user location.
• Log Files: System logs must be in UTC to create a coherent timeline of events, especially when debugging issues across a distributed network.
• Financial Transactions: Global financial markets rely on UTC to provide a single, legally binding timestamp for all transactions.