Time Zones

Reference

Coordinated Universal Time (UTC) vs Greenwich Mean Time (GMT)
- Naming: UTC was adopted for a single, multilingual acronym, replacing GMT as the official standard.
- For most people: UTC and GMT are the same (UTC+0 = GMT+0).
- Technically: UTC is more precise and technologically advanced (atomic clocks), while GMT is tied to the Earth's (slightly variable) rotation.
Zulu time is a communications term meaning UTC (often written with a “Z” suffix, e.g., 1430Z), widely used in aviation and meteorology. FAA explicitly states it uses UTC for operations and “ZULU” may denote UTC; NOAA also describes “Zulu time (Z)” as UTC. ¹⁾

CST (Central Standard Time) = UTC - 6
- Used roughly November to March
- Example: Chicago time is 5 PM CST which is 11 PM UTC

CDT (Central Daylight Time) = UTC - 5
- Used roughly March to November
- Daylight Saving Time (DST) is in effect during this period, meaning clocks are set forward one hour (“spring forward, fall back”) to provide more evening daylight in warmer months.
- Example: Chicago time is 3 PM CDT which is 8 PM UTC

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