24

There are 24 letters in the Greek alphabet (modern Greek). Greek was the first alphabet to write vowels as letters in their own right, which is why every European alphabet descends from it rather than directly from Phoenician.

Pure gold. The karat scale is twenty-fourths, so 24 karat is 24/24 — in practice 999 parts per thousand or finer, since absolute purity is not achievable. The scale is karat with a K — a proportion of gold in an alloy — and is not the carat with a C used for gemstones, which is a unit of mass equal to 200 milligrams. A one-carat diamond and 24-karat gold have nothing in common but a homophone.

There are 24 hours in a day.

24 divides the day into 24 hours under the modern 24-hour clock convention, a near-universal civil timekeeping standard adopted worldwide alongside (and often in place of) the 12-hour clock.

The 24-hour day descends from ancient Egyptian timekeeping, which tracked night by the rising of twelve 'decan' stars and divided daylight into twelve parts as well. Those 24 divisions were originally unequal — they lengthened and shortened with the seasons — and only became fixed, equal hours much later, with the spread of mechanical clocks.

There are 24 prefixes in the International System of Units (worldwide, SI, since 2022). Twenty for a century, then ronna, quetta, ronto and quecto were added in 2022 — partly because the quantity of data in the world was on course to outgrow the largest prefix available.

There are 24 pairs of chromosomes in a chimpanzee cell (chimpanzees, bonobos, gorillas and orangutans). Humans have 23 pairs, and the difference is a single fusion: human chromosome 2 corresponds to two separate ape chromosomes, complete with the remains of telomeres in the middle where they joined.

24 is the atomic number of chromium, best known for its use in stainless steel and decorative plating.

24 December is Christmas Eve, observed in Christian communities worldwide; the principal celebration day in much of Northern and Central Europe and Latin America. In Germany, Scandinavia, Poland, Czechia and much of Latin America the main family meal and gift exchange happen on the evening of 24 December rather than on Christmas Day. This reflects the older liturgical convention in which a feast day begins at sunset on the preceding evening.

In Jainism, twenty-four Tirthankaras are recognised in the present cosmic age. Mahavira, a contemporary of the Buddha, is the twenty-fourth and last. The tradition treats the series as the reviving of a teaching rather than its founding, which is why he is not counted as its origin. This is a scholarly account rather than the tradition's own framing.

Presented as belief or tradition, not as an established fact.

In Jainism, twenty-four tirthankaras are recognised in the current cosmic age. Mahavira is the twenty-fourth and the only one whose historicity is broadly accepted outside the tradition; Parshvanatha, the twenty-third, is placed by some historians in the ninth century BCE.

Presented as belief or tradition, not as an established fact.

There are 24 bits in true colour, eight per channel. That gives 16,777,216 distinct colours, which is 256 cubed.

The Le Mans endurance race is 24 hours (France, since 1923). An endurance race is defined by time rather than distance, which is the point: the winner is whoever covers the most ground before the clock stops, so reliability counts as much as speed.

'24/7' — twenty-four hours a day, seven days a week — is common English shorthand for something continuously available. It came into wide use late in the 20th century, and pairs the hours in a day with the days in a week rather than with any other timekeeping figure.

24's real-time constraint required every episode to cover exactly one hour, clock included. The device was widely praised and very rarely imitated, because it makes ordinary storytelling extremely difficult.

There are 24 time zones in the basic scheme, though the real count is higher (worldwide; offsets of 30 and 45 minutes exist).