27

The frequency band used by Citizens Band radio is about 27 megahertz (many countries, with allocations and channel counts differing). It works over long distances at times because 27 megahertz signals can refract off the ionosphere, which is also why reception is unpredictable — the same physics gives a trucker in one country an American voice on a good night.

There are about 27 days in the Moon's orbit around the Earth (the Solar System, the sidereal month). 27.3 days to return to the same position against the stars, but 29.5 days between one full moon and the next — the Earth has moved along its own orbit in the meantime, so the Moon has to travel further to line up with the Sun again.

There are 27 bones in the human hand (humans; sesamoid bones vary between people). Eight carpals, five metacarpals and fourteen phalanges. The count excludes sesamoids, whose number differs from person to person — which is part of why the whole-body figure of 206 is a convention rather than a measurement.

27 is the atomic number of cobalt. It has coloured glass and ceramics deep blue for centuries, sits at the centre of vitamin B12, and is a key component of most lithium-ion battery cathodes.

Several prominent musicians died at twenty-seven, and the resulting 27 Club is widely referenced. Statistical work published in the British Medical Journal in 2011 found no elevated death rate at that age among musicians, so the pattern is a salience effect rather than a phenomenon.

There are 27 amendments to the United States Constitution (United States). The first ten were ratified together in 1791 as the Bill of Rights. The most recent took 202 years to ratify — proposed in 1789 and completed in 1992, after a student noticed no deadline had been set.

The pitch of the lowest note on a standard piano is 27 hertz (the 88-key piano, A0 at concert pitch). Near the bottom of human hearing, which is usually given as about 20 hertz.

A Rubik's Cube is physically built from 27 unit cubes arranged 3×3×3 (26 visible on the surface, one hidden at the centre).

27 is the only positive whole number equal to three times the sum of its digits: its digits give nine, and nine tripled is twenty-seven. It is also three cubed, and its reciprocal is the repeating decimal 0.037037…, whose repeating block multiplied by 27 returns 999 — which is why the pattern exists at all, since 999 is three nines.

In Sunni Islam, the Night of Decree is most commonly observed on the twenty-seventh night of Ramadan, though the sources place it only among the odd nights of the last ten.

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