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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 21 600 nmi. A minute of arc is π / 10 800 of a radian. A second of arc, arcsecond (abbreviated as arcsec), or arc second, denoted by the symbol ″, [2] is a unit of angular ...
Length of one degree (black), minute (blue) and second (red) of latitude and longitude in metric (upper half) and imperial units (lower half) at a given latitude (vertical axis) in WGS84. For example, the green arrows show that Donetsk (green circle) at 48°N has a Δ long of 74.63 km/° (1.244 km/min, 20.73 m/sec etc) and a Δ lat of 111.2 km ...
With this value for R the meridian length of 1 degree of latitude on the sphere is 111.2 km (69.1 statute miles) (60.0 nautical miles). The length of one minute of latitude is 1.853 km (1.151 statute miles) (1.00 nautical miles), while the length of 1 second of latitude is 30.8 m or 101 feet (see nautical mile).
A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. [2] [3] [4] Historically, it was defined as the meridian arc length corresponding to one minute ( 1 / 60 of a degree) of latitude at the equator, so that Earth's polar circumference is very near to 21,600 nautical miles (that is 60 minutes × 360 degrees).
As one degree is 1 / 360 of a circle, one minute of arc is 1 / 21600 of a circle – such that the polar circumference of the Earth would be exactly 21,600 miles. Gunter used Snellius's circumference to define a nautical mile as 6,080 feet, the length of one minute of arc at 48 degrees latitude. [24]
360 degrees (°) in a full circle; 60 arc-minutes (′) in one degree; 60 arc-seconds (″) in one arc-minute; To put this in perspective, the full Moon as viewed from Earth is about 1 ⁄ 2 °, or 30 ′ (or 1800″). The Moon's motion across the sky can be measured in angular size: approximately 15° every hour, or 15″ per second.
The latitude of the circle is approximately the angle between the Equator and the circle, with the angle's vertex at Earth's centre. The Equator is at 0°, and the North Pole and South Pole are at 90° north and 90° south, respectively. The Equator is the longest circle of latitude and is the only circle of latitude which also is a great circle.
where φ (°) = φ / 1° is φ expressed in degrees (and similarly for β (°)). On the ellipsoid the exact distance between parallels at φ 1 and φ 2 is m(φ 1) − m(φ 2). For WGS84 an approximate expression for the distance Δm between the two parallels at ±0.5° from the circle at latitude φ is given by