8

In Cantonese and Mandarin, 8 (八, bā) closely resembles the word for 'prosper' or 'wealth' (發, fā), making it one of the most sought-after numbers in Chinese-speaking contexts for phone numbers, addresses and prices.

An octave is named for the eighth note of a diatonic scale, counting the starting note as one. Going up an octave doubles the frequency, and the two notes sound so alike that most musical traditions treat them as the same note in a different register — which is why the naming repeats every eight steps.

8 March is International Women's Day, observed in internationally; a public holiday in some countries. Marked since the early twentieth century and recognised by the United Nations from 1975. It is an official public holiday in a number of countries and a working day marked by events in many others.

A superstition in Chinese-speaking cultures holds that eight is sought after because its spoken form resembles the word for prosperity, and numbers containing it sell at a premium (China and Chinese-speaking communities). The 2008 Beijing Olympics opened at 8:08 pm on 8 August. Vehicle registrations and phone numbers heavy in eights have repeatedly sold at auction for large sums, which makes this one of the few superstitions with a directly observable price. This is a scholarly account rather than the tradition's own framing.

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

In Japanese-speaking contexts, it is traditional that eight is treated as fortunate, associated with the shape of the character, which widens towards the base and is read as prospects broadening. This is a scholarly account rather than the tradition's own framing.

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

There are 8 bits in a byte (worldwide, since the 1960s). Not a law of nature: earlier machines used six, seven or nine. The IEC term for exactly eight is 'octet', used in standards precisely because 'byte' once meant other things.

There are more than 8 billion mobile phone subscriptions. Figure as of 2023. More subscriptions than there are people, because many people hold more than one and inactive accounts linger in the counts.

A byte, the fundamental unit of digital storage and memory addressing, is defined as 8 bits — the reason storage capacities and character encodings are built around multiples of 8.

There are 8 legs on a spider and other arachnids (arachnids, including scorpions, ticks and mites).

There are 8 arms on an octopus (octopuses).

There are 8 planets in the Solar System (worldwide, under the IAU's 2006 definition). The definition requires a body to have cleared its orbital neighbourhood, which is the clause Pluto fails. It was adopted by a vote of astronomers, not discovered.

There are about 8 minutes of travel for light from the Sun to the Earth (the Solar System, at the average distance). Eight minutes and twenty seconds. The Sun could go out and nobody would know for that long — which is the most direct demonstration that looking at anything distant is looking into the past.

There are roughly 8 million species on Earth. Estimates range from about 5 to over 10 million. About 1.2 million have been formally described, so most of the estimate is inferred rather than catalogued.

The density of steel is about 8 thousand kilograms per cubic metre (worldwide, common carbon steels). 7,850 kg/m³, eight times water. Aluminium is about 2,700 and titanium about 4,500, which is the whole argument in aerospace.

8 is the atomic number of oxygen, essential for respiration in most living organisms and the second most abundant gas in Earth's atmosphere.

There are 8 billion people alive. Figure as of 2022. The world passed this figure in late 2022, having passed one billion around 1804.

There are roughly 8 million lightning strikes on Earth each day. Around a hundred every second, most of them over land in the tropics.

There are roughly 8 million tonnes of plastic entering the ocean each year. A widely used 2015 estimate with a published range of 4.8 to 12.7 million tonnes. Later work using different methods has produced both higher and lower figures.

8 is 2³. That is precisely why a byte of 8 bits holds 256 distinct values (2⁸): each added bit doubles the range, so the byte's capacity follows from 8 being a power of two rather than from any separate convention.

In Judaism, a boy is circumcised on the eighth day after birth, a timing stated in Genesis and kept even when it falls on the Sabbath.

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

In Buddhism, the path set out in the fourth noble truth has eight limbs, described as mutually supporting rather than as stages taken in order.

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

In Buddhism, the path set out in the fourth of the Noble Truths has eight factors. The eight are conventionally grouped into three trainings — ethical conduct, mental discipline and wisdom — and are described as mutually supporting rather than sequential, despite the numbering. This is a scholarly account rather than the tradition's own framing.

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