minute

(′)

   a historic unit of proportion equal to 1/60. The Romans lacked our flexible terminology for fractions; they followed Babylonian and Greek practice in visualizing quantities as being divided into 60 parts, so they could express fractions consistently in 60ths. A 60th part was called a pars minuta prima ("first small part") of the whole. For smaller fractions, a 60th part was divided into 60 smaller parts, each called a pars minuta secunda ("second small part"). The minuta prima has come down to us as "minute," the minuta secunda is our "second," and the prima leads to the traditional symbol ′ being called a "prime."

   1. (min or ′ or m)

   a unit of time equal to 60 seconds or to 1/60 hour. The SI specifies min as the symbol for the time unit and ′ as the symbol for the minute of arc (see below).

   2. (′ or m or moa) or minute of arc or minute of angle

   a unit of angular measure equal to 60 arcseconds or to 1/60 degree. This unit is often called the arcminute to distinguish it from the minute of time. There are 21 600 arcminutes in a circle. The SI defines min as the symbol for the time unit (see above) and recommends ′ as the symbol for the minute of arc. The symbol moa is often used in target shooting. The international standard ISO 31 requires that angles be stated in degrees and decimal fractions of the degree, without use of arcminutes and arcseconds.

   3. (′ or m)

   a unit of angular measure used in astronomy. Astronomers measure right ascension (see hour²) in time units by dividing the equator into 24 hours instead of 360 degrees. This makes 1 minute of right ascension equal to 15 arcminutes.

   4. a unit of time equal to 1/60 day or 24 minutes in the modern sense. This was the original definition of the minute as a unit of time. The modern definition of 1/60 hour did not appear until the invention of mechanical clocks made it practical to measure such small intervals of time.

   5. (min or m or ′)

   a unit of sidereal time in astronomy; see sidereal day.