International System of Units (SI)
A day, symbol d, is defined as 86,400 seconds. The second is the unit of time in SI units.
A day on the UTC time standard can include a negative or positive leap second, and can therefore have a length of 86,399 or 86,401 seconds.
The International Bureau of Weights and Measures (BIPM) currently defines a second as
… the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium 133 atom.
This makes the SI-based day last exactly 794,243,384,928,000 of those periods.
Read more about this topic: Day
Famous quotes containing the words system and/or units:
“There are obvious places in which government can narrow the chasm between haves and have-nots. One is the public schools, which have been seen as the great leveler, the authentic melting pot. That, today, is nonsense. In his scathing study of the nation’s public school system entitled “Savage Inequalities,” Jonathan Kozol made manifest the truth: that we have a system that discriminates against the poor in everything from class size to curriculum.”
—Anna Quindlen (b. 1952)
“Even in harmonious families there is this double life: the group life, which is the one we can observe in our neighbour’s household, and, underneath, another—secret and passionate and intense—which is the real life that stamps the faces and gives character to the voices of our friends. Always in his mind each member of these social units is escaping, running away, trying to break the net which circumstances and his own affections have woven about him.”
—Willa Cather (1873–1947)