What is Timezone?
Timezone is a region of the globe that observes a uniform standard time for legal, commercial, and social purposes, typically defined as an offset from Coordinated Universal Time (UTC).
Quick Facts
| Full Name | Time Zone |
|---|---|
| Created | 1884 (International Meridian Conference) |
| Specification | Official Specification |
How It Works
Time zones were established to standardize timekeeping across different geographical regions. The world is divided into 24 primary time zones, each roughly 15 degrees of longitude wide. Time zones are expressed as offsets from UTC (e.g., UTC+8 for China Standard Time). Daylight Saving Time (DST) adds complexity by shifting clocks forward or backward seasonally in some regions. Proper timezone handling is crucial in software development for scheduling, logging, and international applications.
Key Characteristics
- Based on UTC offset (e.g., UTC-5, UTC+9)
- 24 primary zones spanning the globe
- Some regions observe Daylight Saving Time
- Named zones like 'America/New_York' or 'Asia/Shanghai'
- Critical for international applications
- Affects scheduling, logging, and data timestamps
Common Use Cases
- Scheduling meetings across different regions
- Displaying local time in web applications
- Logging events with accurate timestamps
- Converting between different time zones
- Handling Daylight Saving Time transitions
Example
Loading code...Frequently Asked Questions
What is the difference between UTC and GMT?
UTC (Coordinated Universal Time) and GMT (Greenwich Mean Time) are often used interchangeably, but they are technically different. GMT is a time zone based on the mean solar time at the Royal Observatory in Greenwich, London. UTC is a time standard that is kept using atomic clocks and is more precise. For most practical purposes, they are the same, but UTC is the international standard used in computing and aviation.
How do I convert between time zones in JavaScript?
You can use the toLocaleString() method with the timeZone option, or use libraries like Luxon, date-fns-tz, or Moment Timezone. For example: new Date().toLocaleString('en-US', { timeZone: 'America/New_York' }) will display the current time in New York. For more complex operations, dedicated libraries provide better timezone database support.
Why do some time zones have 30 or 45 minute offsets?
While most time zones are offset by whole hours from UTC, some regions chose offsets that better align with their geographic position or for historical/political reasons. India uses UTC+5:30, Nepal uses UTC+5:45, and parts of Australia use UTC+9:30. These non-standard offsets allow these regions to have more appropriate local times relative to solar noon.
What is Daylight Saving Time and how does it affect time zones?
Daylight Saving Time (DST) is a practice of advancing clocks by one hour during warmer months to extend evening daylight. Not all regions observe DST, and the dates when clocks change vary by country. This means a timezone's UTC offset can change during the year. For example, US Eastern Time is UTC-5 in winter but UTC-4 during DST. This complexity must be handled carefully in software.
What is the IANA timezone database?
The IANA (Internet Assigned Numbers Authority) timezone database, also known as tz database or zoneinfo, is the authoritative source for timezone information worldwide. It contains historical and current timezone rules for all regions, including DST transitions. Timezone names like 'America/New_York' or 'Asia/Tokyo' come from this database. Most programming languages and operating systems use this database for timezone conversions.