This is much exaggerated in the diagram above. At the higher latitudes near the poles where the Earth is slightly flatter, the curvature of the surface can be described by an arc of larger radius, and therefore each degree of latitude is larger and slightly longer (about 69.4 miles / 111.7 km at 89°). Many monuments and signs on the 45th Parallel declare that the latitude is "Halfway between the North Pole and the Equator", but again this is not precisely true due to the distortion caused by the Earth's rotation. At the 45th Parallel, the two latitudes are a maximum of 11.5' or about 13 miles / 21 km apart. The flattened shape means that the geocentric latitude and geodetic latitude angles deviate increasingly between the equator and the poles. The Earth's diameter at the equator is about 7926 miles / 12,756 km while its polar diameter is about 7900 miles / 12,713 km, meaning that the radius at the Equator bulges about 13 miles / 21 km farther from the center than at the poles (much exaggerated in the stylized cross-section diagram above). In the old days this was done by measuring the angle of the noonday sun, or a star such as the north star Polaris, in relation to a precisely horizontal level or a perfectly vertical plumb line.īecause the earth's rotation causes the planet to bulge slightly at the equator and flatten at the poles, it is distorted into an ellipsoid or oblate spheroid. However, surveyors and geographers measure the geodetic latitude, or the angle of a vertical "normal" line from a point on the earth's surface to the plane of the equator. Geocentric latitude measures the angle from the plane of the equator at the center of the earth to a point on the surface, which is what many people assume is marked by the 45th Parallel. Latitude is measured in degrees north or south from 0 degrees at the equator to 90 degrees at the poles, while longitude is measured in degrees east or west from the arbitrary 0-degree Prime Meridian at Greenwich, England. Geographers divide the earth into lines of latitude which run east-west on planes parallel to the equator, and lines of longitude which run north-south converging at the poles. Sun-seekers living in Lincoln City, Oregon and Minneapolis, Minnesota can take comfort knowing that the residents of Turin, Italy receive exactly the same length of daylight on the other side of the earth. What do these disparate regions of the earth have in common? Only that every day the sun will shine down on each place at exactly the same angle. If you stand on this line, you may not realize that the same latitude connects the mountains of Yellowstone and the piney woods of Maine to the wine regions of Bordeaux, the Crimean peninsula, the Gobi Desert of Mongolia, and the snowy northern tip of Hokkaido, Japan. Halfway between the North Pole and the Equator,