Articles

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, Cloudflare, and Google.

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.

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.

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 URLs and currencies to IBAN accounts and Olympic uniforms.

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.

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.