MetricationMetrication or metrification is the act or process of converting to the metric system of measurement. All over the world, countries have transitioned from local and traditional units of measurement to the metric system. This process began in France during the 1790s, and is still continuing more than 200 years later, with the modern International System of Units, as the metric system has not been fully adopted in all countries and areas. Today, most countries have the metric system as their official system of measurement.
Nautical mileA nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. Historically, it was defined as the meridian arc length corresponding to one minute (1/60 of a degree) of latitude at the equator. Today the international nautical mile is defined as . The derived unit of speed is the knot, one nautical mile per hour. There is no single internationally agreed symbol, with several symbols in use. NM is used by the International Civil Aviation Organization.
MetreThe metre (or meter in American spelling; symbol: m) is the base unit of length in the International System of Units (SI). The metre was originally defined in 1791 as one ten-millionth of the distance from the equator to the North Pole along a great circle, so the Earth's circumference is approximately 40000 km. In 1799, the metre was redefined in terms of a prototype metre bar. The actual bar used was changed in 1889. In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86.
International System of UnitsThe International System of Units, internationally known by the abbreviation SI (for Système International), is the modern form of the metric system and the world's most widely used system of measurement. Established and maintained by the General Conference on Weights and Measures (CGPM), it is the only system of measurement with an official status in nearly every country in the world, employed in science, technology, industry, and everyday commerce.
Conversion of unitsConversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors which change the measured quantity value without changing its effects. Unit conversion is often easier within the metric or the SI than in others, due to the regular 10-base in all units and the prefixes that increase or decrease by 3 powers of 10 at a time. The process of conversion depends on the specific situation and the intended purpose.
ParsecThe parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and is defined as the distance at which 1 AU subtends an angle of one arcsecond (1/3600 of a degree). The nearest star, Proxima Centauri, is about from the Sun. Most stars visible to the naked eye are within a few hundred parsecs of the Sun, with the most distant at a few thousand.
Astronomical system of unitsThe astronomical system of units, formerly called the IAU (1976) System of Astronomical Constants, is a system of measurement developed for use in astronomy. It was adopted by the International Astronomical Union (IAU) in 1976 via Resolution No. 1, and has been significantly updated in 1994 and 2009 (see astronomical constant). The system was developed because of the difficulties in measuring and expressing astronomical data in International System of Units (SI units).
