Meridian (geography)

The position of a point along the meridian at a given longitude is given by its latitude, measured in angular degrees north or south of the Equator.

Adopting instead a spheroidal or ellipsoid model of Earth, the meridian is half of a north-south great ellipse.

The second was that in the late 19th century, 72% of the world's commerce depended on sea-charts which used Greenwich as the Prime Meridian.

The recommendation was based on the argument that naming Greenwich as Longitude 0º would be of advantage to the largest number of people.

As 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 through Greenwich, and is at 180° longitude near the International Date Line (with land mass and island deviations for boundary reasons).

The position of the prime meridian has changed a few times throughout history, mainly due to the transit observatory being built next door to the previous one (to maintain the service to shipping).

It was in the best interests of the nations to agree to one standard meridian to benefit their fast growing economy and production.

[10] The argument of which meridian is more scientific was set aside in order to find the most convenient for practical reasons.

However, a compass needle will not be steady in the magnetic meridian, because of the longitude from east to west being complete geodesic.

When he noted the sight line for the True Meridian from his family's house to the depot, he could check the declination of his compass before and after surveying throughout the day.

[19] The meridian passage will not occur exactly at 12 hours because of the Earth orbit excentricity (see Equation of time).

[21][22][23] Although, a few time zones are offset by an additional 30 or 45 minutes, such as in the Chatham Islands, South Australia and Nepal.

These instruments also were typically affected by local gravity, which paired well with existing technologies such as the magnetic meridian.