The concept of longitude was first developed by ancient Greek astronomers. Hipparchus (2nd century BC) used a coordinate system that assumed a spherical earth and divided it into 360°, as we still do today. Its main meridian ran through Alexandria. [3]:31 He also proposed a method for determining longitude by comparing the local time of a lunar eclipse at two different locations, thus demonstrating an understanding of the relationship between longitude and time. [3]: 11 . [4] Claudius Ptolemy (2nd century AD) developed a mapping system with curved parallels that reduced distortions. It has also collected data for many sites, from the UK to the Middle East. He used a prime meridian across the Canary Islands, so all longitudes would be positive. While Ptolemy`s system was robust, the data he used was often poor, resulting in a gross overestimation (by about 70%) of the length of the Mediterranean. [5] [6]: 551–553 [7] Like latitudes, longitudes are measured in degrees and minutes, and sometimes seconds. Longitude refers to the angle created by drawing the following: Longitude lines, also called meridians, are imaginary lines that divide the Earth.
They go from north to south from one pole to another, but measure the distance to the east or west. The first to propose a method of measuring longitude was the explorer Amerigo Vespucci. In the late 1400s, he began measuring and comparing the positions of the Moon and Mars with their simultaneously predicted positions over several nights (diagram). In his measurements, Vespucci calculated the angle between its location, the moon and Mars. In this way, Vespucci obtained a rough estimate of longitude. However, this method was not widely used because it was based on a specific astronomical event. Observers also needed to know the exact time and measure the positions of the Moon and Mars on a stable viewing platform, which was difficult to accomplish at sea. Latitude is the angle created by two connecting lines: the line that connects the latitude and center of the Earth, and the line that connects the equator to the center of the Earth. Where these two lines meet, they form an angle that determines the north-south position of a particular place on Earth. Today, longitude is measured more accurately with atomic clocks and satellites. The Earth is always uniformly divided into 360° longitude, with 180° east of the prime meridian and 180° west. Longitude coordinates are divided into degrees, minutes, and seconds, where 60 minutes is one degree and 60 seconds is one minute.
For example, the longitude of Beijing, China is 116°23`30″E. The 116° indicates that it is close to the 116th meridian, while the minutes and seconds indicate how close it is to this line. The “E” indicates that it is this distance east of the prime meridian. Although less common, longitude can also be written in decimal degrees. The location of Beijing in this format is 116.391°. For centuries, sailors and explorers have worked to determine their longitude to facilitate navigation. Latitude was easily determined by observing the inclination of the sun or the position of known stars in the sky and calculating the angular distance from the horizon to them. Longitude could not be determined in this way, because the rotation of the Earth constantly changes the position of the stars and the Sun.
In the early 1600s, a new idea of measuring longitude was developed when Galileo discovered that it could be measured with two clocks. He said each point on Earth took 24 hours to travel the full 360° rotation of the Earth. He found that if you divide 360° by 24 hours, you find that a point on Earth moves at 15° longitude every hour. Therefore, with an accurate watch at sea, a comparison of two watches would determine longitude. One clock would be in the home port and the other on the ship. The ship`s clock should be reset to noon every day. The time difference would then indicate the difference in length traveled, since one hour represents a change in longitude of 15°. Longitude (/ˈlɒndʒɪtjuːd/, AU and UK also /ˈlɒŋɡɪ-/)[1][2] is a geographic coordinate that indicates the east-west position of a point on the surface of the Earth or other celestial body.
It is an angular measure, usually expressed in degrees, denoted by the Greek letter lambda (λ). Meridians are semicircular lines that run from one pole to another and connect points of the same longitude. The prime meridian defines 0° longitude; The international reference meridian for the Earth conventionally passes near the Royal Observatory in Greenwich, England, on the island of Great Britain. Positive longitudes are east of the prime meridian and negative longitudes are west. On a map (diagram), longitudes are the vertical lines that run from the North Pole to the South Pole and are perpendicular to the lines of latitude. Each line of longitude also crosses the equator. Since longitudes are not parallel, they are called meridians. Like parallels, meridians name the specific line and indicate the distance east or west of a 0° line.
The meridians converge at the poles and are furthest from each other at the equator (about 69 miles (111 km) away). A geographic mile is defined as the length of one minute of arc along the equator (one minute of equatorial longitude), so a longitude along the equator is exactly 60 geographical miles, or 111.3 kilometers, since there are 60 minutes in a degree. The 1-minute length along the equator is 1 geographic mile or 1,855 km or 1,153 miles, while the 1-second length is 0.016 geographic miles or 30.916 m or 101.43 feet. Note that longitude at the poles is singular and calculations accurate enough for other positions may be inaccurate at or near the poles. The meridian discontinuity of ±180° should also be treated with caution in the calculations. An example is a calculation of the eastward displacement by subtracting two longitudes, which gives the wrong answer if both positions are on either side of this meridian. To avoid this complexity, you must replace latitude and longitude with a different horizontal position representation in the calculation. Unlike latitudes, which are parallel to the equator, vertical longitudes or imaginary circles go in a north-south direction and therefore intersect with the equator.
Half of a longitudinal circle is called the meridian. The meridians are perpendicular to the equator and at any degree of latitude. Locally, NOAA`s National Geodetic Survey manages the continuously operating reference station network, which includes 1,800 permanently operating fixed GPS stations. These CORS continuously receive GPS radio signals and integrate these data into the National Spatial Reference System. The GPS position on a smartphone is accurate to about 5 meters (16 feet), but the CORS data processed can provide longitude accuracy down to a few centimeters, as well as latitude and elevation positions. COS φ decreases from 1 at the equator to 0 at the poles, which measures how the latitude circles narrow from the equator to a point at the pole, so the length of a longitude also decreases. This contrasts with the slight increase (1%) in the longitude of a latitude (north-south distance), from the equator to the pole. The table shows both for the WGS84 ellipsoid with a = 6378137.0 m and b = 6356752.3142 m. Note that the distance between two points at a distance of 1 degree on the same circle of latitude, measured along this circle of latitude, is slightly greater than the shortest (geodesic) distance between these points (except at the equator, where they are the same); The difference is less than 0.6 m (2 ft). Each longitude is divided into 60 minutes, each divided into 60 seconds.
A longitude is thus given in sexagesimal notation as, for example, 23° 27′ 30″ E. For greater precision, seconds are specified with a decimal fraction. An alternative representation uses degrees and minutes, and parts of a minute are expressed in decimal notation, thus: 23° 27.5′ E. Degrees can also be expressed as a decimal fraction: 23.45833° E. For calculations, the angular measure can be converted to radians, so longitude can also be expressed in this way as a signed fraction of π (pi) or as an unsigned fraction of 2π. The distance per degree of longitude is about 69.18 miles (111.32 km) to the equator and 0 to the poles. Every place on Earth is expressed in terms of latitude and longitude. Together, the latitude and longitude circles show where a particular place on Earth is located relative to the prime meridian and the equator. It wasn`t until the 18th century that people were able to correctly determine their longitude, although they had been able to determine latitude for some time.
Not being able to calculate longitude was dangerous for sailors. Without an exact location, they could easily run out of food or water on a long expedition into uncharted territory. Christopher Columbus made two attempts to use lunar eclipses to discover its longitude, the first on Saona Island on September 14, 1494 (second voyage) and the second in Jamaica on February 29, 1504 (fourth voyage).