Meridian

Convergence of two meridians.

Meridians go from the north to the south.

The meridians are the imaginary great semicircles of the terrestrial globe that pass through the north and south poles. By extension, they are also the great semicircles that pass through the poles of any reference sphere or spheroid. They are imaginary lines whose main utility is to be able to determine the position (Longitude) of any place on Earth with respect to a reference meridian or 0 meridian, adding the Latitude, determined by the parallel that passes through that point.

They are also used to calculate the time zone. All observers located on the same meridian see at the same time, in the illuminated half of the Earth, the Sun passing through the highest point of its course, that is, noon.

In cartography, the reference meridian 0 is the one that passes through the Greenwich observatory. In astronomy, the reference meridian for equatorial coordinates is the one that passes through the point of Aries, while the reference meridian for the time coordinates is the one that passes through the zenith and the nadir of the place.

The position of a point along the meridian is given by that longitude and its latitude, measured in angular degrees north or south of the equator. Each meridian is perpendicular to all circles of latitude. Meridians are half of a great circle on the Earth's surface. The length of a meridian on a modern ellipsoid model of the earth (WGS 84) has been estimated to be 20,003.93 km (12,429.9 mi).

Before Greenwich

Eratosthenes established the first principal meridian in 200 B.C. This prime meridian was used to measure the earth, but it presented many problems due to the lack of measurement of latitude. Many years later, around the 19th century, there were still concerns about the prime meridian. Multiple locations for the geographic meridian meant there was inconsistency, because each country had its own guidelines for where the prime meridian was located.

Etymology

The term meridian comes from the Latin meridies, which means "noon"; the subsolar point passes through a given meridian at solar noon, halfway between the times of sunrise and sunset on that meridian. Likewise, the Sun crosses the celestial meridian at the same time. The same Latin root gives rise to the terms a. m. (ante meridien) and p. m. (post meridien) which are used to disambiguate the times of day when using the 12-hour clock.

International Meridian Conference

Due to a growing international economy, there was a demand for an established international prime meridian to facilitate worldwide travel, which in turn would improve international trade between countries. As a result, a Conference was held in 1884, in Washington, D.C. Twenty-six countries were present at the International Meridian Conference to vote on an international prime meridian. Ultimately, the result was the following:

1. There would be one meridian,
2. Meridian had to cross and pass in Greenwich (which was 0 °),
3. There would be two length directions up to 180 ° (the east is more and the west is less),
4. There will be a universal day,
5. The day starts at midnight of the initial meridian.

“There were two main reasons for this. The first was that the US had already chosen Greenwich as the base for its own national time zone system. The second was that at the end of the 19th century, 72% of world trade depended on maritime charts that used Greenwich as prime meridian. The recommendation was based on the argument that naming Greenwich Longitude 0º would be to the advantage of the greatest number of people."

Geography

By the end of the 12th century, there were two major places recognized as the geographic location of the meridian, France and Great Britain. These two locations often conflicted and an agreement was reached only after an International Meridian Conference was held, at which Greenwich was recognized as the 0° location.

The meridian through Greenwich (within Greenwich Park), England, called the Prime Meridian was fixed at zero degrees longitude, while other meridians were defined by the angle at the center of the earth between where east and where prime meridian crosses the equator. Since there are 360 degrees in a circle, the meridian on the opposite side of the earth from Greenwich, the antimeridian, forms the other half of a circle with the one that passes through Greenwich, and is 180° longitude near the date line. international (with land mass and island deviations for boundary reasons). The meridians from West of Greenwich (0°) to the antimeridian (180°) define the Western Hemisphere and the meridians from the East of Greenwich (0°) to the antimeridian (180°) define the Eastern Hemisphere. maps show lines of longitude.

The position of the prime meridian has changed several times throughout history, mainly because the transit observatory was built next to it (to maintain navigation service). Such changes did not have a significant practical effect. Historically, the average error in determining longitude was much larger than the change in position. The adoption of the World Geodetic System 84 (WGS84) as the positioning system has moved the geodetic prime meridian 102,478 meters east of its last astronomical position (measured at Greenwich). The position of the geodetic prime meridian Today it is not identified at all by any kind of sign or mark in Greenwich (as the oldest astronomical position was), but it can be located using a GPS receiver.

Effect of Prime Meridian (Greenwich Mean Time)

It was in the best interest of nations to agree on a standard meridian to benefit their rapidly growing economy and production. The disorganized system they had before was not enough for their increasing mobility. Coach services in England had erratic timing before the GWT. The United States and Canada were also upgrading their rail system and needed standard time as well. With a standard meridian, stagecoach and trains could be more efficient. The argument of which meridian is more scientific was set aside to find the most convenient for practical reasons. They could also agree that the universal day was to be the mean solar day. They agreed that the days would begin at midnight and that the universal day would not affect the use of local time. A report was submitted to the "Transactions of the Royal Society of Canada", dated May 10, 1894; on the "Unification of Astronomical, Civil and Nautical Days"; which stated that:

• Civil day - starts at midnight and ends at the next midnight,
• Astronomical day - begins at noon of the civil day and continues until the next noon, and
• Nautical day - concludes at noon of the civil day, beginning at the previous noon.

Local Meridian

1. Parallel (Circle of latitude); 2. Meridian reference origin.

By agreement made at an international conference held in 1884 in Washington and sponsored by the then President of the United States, Chester A. Arthur, which was attended by delegates from 25 countries, the "reference meridian", from which the longitudes are measured, that is, the one considered the "meridian 0°", is the Greenwich meridian, so called because it passes through the old Greenwich astronomical observatory (which, at the time, was a suburb of London). The choice was made not only because London was the capital of the most important empire at the time, but also because the 180 meridian, which determines the change of day, is in a very sparsely inhabited area.

The local meridian, also called the local meridian or simply meridian, is the meridian that passes through the point where the the observer. The term "meridian" comes from the Latin meridies, which means "noon"; the sun crosses a given meridian halfway between sunrise and sunset on that meridian; on the opposite meridian or antimeridian it is midnight.

The time zones were established from the Meridian of Greenwich. From degree 0 and towards the east the hour will increase, and towards the west, the hour will decrease. The Greenwich meridian is also used to know the longitude of any point on the earth's surface, that is, the distance between any point and the Greenwich meridian. In this way you have east longitude if you move to the right and west longitude if you move to the left.

Setting the hours

The meridian is used to set time. Solar time is different for each meridian. This is due to the rotation of the Earth. By the time a worker from Madrid prepares for lunch, the one from Moscow has already begun his afternoon work, and the one from Peking has finished his workday. At the same time, in New York the great morning rush to offices and factories begins, while in San Francisco people are still sleeping.

The Greenwich meridian was taken as the place for the reference time and the antimeridian as the place of change of day. In this way, the time zones located to the west and vice versa, those to the east, will have one more hour for each time zone.

Magnetic Meridian

The magnetic meridian is an equivalent imaginary line joining the magnetic south pole and the magnetic north pole, and can be taken as the horizontal component of the lines of magnetic force along the surface of the earth. Thus, a compass needle will be parallel to the magnetic meridian. However, a compass needle will not be fixed on the magnetic meridian, since longitude from east to west is completely geodesic. The angle between the magnetic meridian and the true meridian is the magnetic declination, which is relevant for navigation with compass. Navigators could use the azimuth (the horizontal angle or direction of a compass heading) of the rising and setting Sun to measure magnetic variance (difference between magnetic and true north).