First worldwide view of a key phytoplankton proxy

From vast, swirling blooms to minuscule populations, photosynthetic phytoplankton drifting near the surface of the ocean are often captured in snapshots from chlorophyll-detecting satellites. However, phytoplankton at greater ...

A powerful solar storm hit Earth back in 1582

"A great fire appeared in the sky to the North, and lasted three nights," wrote a Portuguese scribe in early March, 1582. Across the globe in feudal Japan, observers in Kyoto noted the same fiery red display in their skies, ...

Shrubs and soils: A hot topic in the cool tundra

Climate change is rapid in the Arctic. As the climate warms, shrubs expand towards higher latitudes and altitudes. Researcher Julia Kemppinen together with her colleagues investigated the impacts of dwarf shrubs on tundra ...

High greenhouse gas emissions from Siberian inland waters

Rivers and lakes at high latitudes are considered to be major sources for greenhouse gas emissions to the atmosphere, but these losses are poorly constrained. In a study published in Nature Communications, Umeå University ...

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Latitude

In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees (marked with °). The equator has a latitude of 0°, the North pole has a latitude of 90° north (written 90° N or +90°), and the South pole has a latitude of 90° south (written 90° S or −90°). Together, latitude and longitude can be used as a geographic coordinate system to specify any location on the globe.

Curves of constant latitude on the Earth (running east-west) are referred to as lines of latitude, or parallels. Each line of latitude is actually a circle on the Earth parallel to the equator, and for this reason lines of latitude are also known as circles of latitude. In spherical geometry, lines of latitude are examples of circles of a sphere, with the equator being a great circle.

Latitude (usually denoted by the Greek letter phi (φ)) is often measured in degrees, minutes and seconds. The Eiffel Tower has a latitude of 48° 51′ 29″ N-- that is, 48 degrees plus 51 minutes plus 29 seconds. Or latitude may be measured entirely in degrees, e.g. 48.85806° N.

If the Earth were actually spherical, and homogenous, and not rotating, then latitude at a point would just be the angle between a vertical line at that point and the plane of the equator. Everywhere on Earth a vertical line would point to the center of the Earth. In reality the earth is rotating and is not spherical, so a vertical line — a line in the direction of apparent gravity — doesn't point to the center of the Earth (except at the poles and the equator). If the Earth were homogenous, then a vertical line would still point to some point on the Earth's axis, and latitude at a point would still be the angle between the vertical line there and the plane of the equator.

But the Earth is not homogenous, and has mountains-- which have gravity and so can shift the vertical line away from the Earth's axis. The vertical line still intersects the plane of the equator at some angle; that angle is astronomical latitude, the latitude you would calculate from star observations. The latitude shown on maps and GPS devices is the angle between a not-quite-vertical line through the point and the plane of the equator; the not-quite-vertical line is perpendicular to the surface of the spheroid chosen to approximate the Earth's sea-level surface, rather than perpendicular to the sea-level surface itself.

This text uses material from Wikipedia, licensed under CC BY-SA