|
Second (arc)
A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a turn. The nautical mile (nmi) was originally defined as the arc length of a minute of latitude on a spherical Earth, so the actual Earth's circumference is very near . A minute of arc is of a radian. A second of arc, arcsecond (abbreviated as arcsec), or arc second, denoted by the symbol , is a unit of angular measurement equal to of a minute of arc, of a degree, of a turn, and (about ) of a radian. These units originated in Babylonian astronomy as sexagesimal (base 60) subdivisions of the degree; they are used in fields that involve very small angles, such as astronomy, optometry, ophthalmology, optics, navigation, land surveying, and marksmanship. To express even smaller angles, standard SI prefixes can be employed; the milliarcsec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ball (association Football)
A football or soccer ball is the ball used in the sport of association football. The ball's spherical shape, as well as its size, mass, and material composition, are specified by Law 2 of the Laws of the Game (association football), Laws of the Game maintained by the International Football Association Board. Additional, more stringent standards are specified by FIFA and other big governing bodies for the balls used in the competitions they sanction. Early footballs began as animal bladders or stomachs that would easily fall apart if kicked too much. Improvements became possible in the 19th century with the introduction of rubber and discoveries of vulcanization by Charles Goodyear. The modern 32-panel ball design was developed in 1962 by Eigil Nielsen (footballer, born 1918), Eigil Nielsen, and technological research continues to develop footballs with improved performance. The 32-panel ball design was soon joined by 24-panel balls as well as 42-panel balls, both of which improv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
