Articles

Find the overlap in working hours, watch the weeks when the US, Europe and Australia change clocks on different dates, and write invites with an explicit zone or UTC.

CST, IST, BST and AST each name several different time zones, and EST is often used in summer when it is wrong. What the common abbreviations mean and what to use instead.

Twice a year about 70 countries move their clocks by an hour. Where the idea came from, who still does it, when the switch happens, and why many have stopped.

Earth rotates 15° per hour, which is why the world is split into 24 time zones. But the actual map is much messier than the rule predicts.

UTC and GMT are used interchangeably and almost always equal. UTC is atomic-clock based, GMT is astronomical — and for precise applications the difference matters.

A leap second is a one-second UTC adjustment that keeps atomic clocks in step with the Earth's rotation. They have caused outages at Reddit, LinkedIn, and Cloudflare.

China spans 60° of longitude with one time zone; Russia spans 170° with eleven. Whether to consolidate or split is driven by politics and identity, not geography.

In everyday use 12 PM is noon and 12 AM is midnight at the start of the day. Why the labels are ambiguous, what NIST recommends, and how to write deadlines clearly.

How to convert between 12-hour and 24-hour time, how military time is written and spoken, what 0000 and 2400 mean, and how Zulu time and zone letters work.

A cheat sheet for ISO 8601: dates, week and ordinal dates, times, UTC offsets, durations and intervals, how RFC 3339 differs, common mistakes, and code examples.

Unix time counts seconds since 1970-01-01 00:00 UTC, ignoring leap seconds. How it works, seconds vs milliseconds, notable timestamps, and why 32-bit clocks fail in 2038.

ISO weeks start on Monday and week 1 is the week with the year's first Thursday. Why 1 January 2027 falls in week 53 of 2026, and how to get the week number in Excel, code and SQL.

A year lasts about 365.2422 days, so the calendar needs a correction. The leap-year rule is a three-line algorithm that keeps the seasons in place.

The seven-day week has no astronomical basis. It came from Babylonian astrology, spread through Judaism and Christianity, and has survived every attempt to replace it.

Solstices and equinoxes are exact instants set by Earth's tilt and orbit. What they are, why the dates shift, UTC times for 2025–2030, and three common myths.

The Moon's phase is the part of its sunlit half we can see from Earth. The eight phase names, the 29.5-day cycle, why it isn't Earth's shadow, and 2027 dates.

Twilight is defined by how far the Sun is below the horizon: 6° for civil, 12° for nautical, 18° for astronomical. What each looks like and why its length varies.

A holiday's name tells you almost nothing about whether you get the day off. The legal categories — public, bank, observance, optional — vary by country and explain why.

Easter is the first Sunday after the first ecclesiastical full moon on or after March 21. The rule is medieval; the date bounces between March 22 and April 25.

Temperature, humidity, and dew point each tell you something different about how the air will feel — together they predict comfort better than any one value alone.

AQI scales compress pollutant readings into one number from 0 to 500. The number alone is meaningless without the scale, dominant pollutant, and local breakpoints.

Somewhere on Earth the date has to change. That place is the International Date Line — a Pacific zigzag that countries have moved more than once.

Every country has three ISO 3166-1 codes — alpha-2, alpha-3, and numeric. You'll see them everywhere from domain names and currencies to IBAN accounts and passports.

Capitals anchor their country's time zone, yet a capital's offset is rarely typical of the country itself. A short tour of political vs temporal geography.