The Shape of the Earth
Earth's Shape
Observable evidence that proves that the Earth is spherical includes:
- The Sinking Ship Observation- Sailing ships appear to sink as they travel away from an observer. In realty, the ships are simply traveling over the Earth's curved surface.
- Lunar Eclipse Shadows- During a lunar eclipse, the Earth casts a rounded shadow on the face of the full moon. If the Earth's shadow always appears rounded, then the Earth must have a spherical shape.
- Equal Pull of Gravity- Regardless of where you are on Earth's surface, the pull of gravity you experience is the same. This means all points on the surface are the same distance from the core so the Earth must be spherical.
- The Altitude of Polaris- The angle of the North Star, Polaris, above the horizon is equal to your latitude. This can only occur on a spherical planet.
- Photos from Space- Modern technology has allowed us to travel into space and photograph the Earth as a whole. This has revealed the true shape of the Earth as a sphere.
While the Earth is spherical in shape, it is not a perfect sphere. 4.6 billion years of constant rotation has caused the Earth to bulge slightly along the equator. As a result the true shape of the Earth is an oblate spheroid, flattened at the poles and slightly bulging at the equator. This true shape is not observable as the shape is so close to being a perfect sphere. Therefore, the best models of the Earth would be perfectly smooth, spherical objects like billiard balls, lacrosse balls or ping-pong balls.
Latitude and Longitude
Latitude is the angular distance you are north or south of the equator (0º latitude). Latitude lines are the parallel, horizontal lines found on a map. Here are some key latitudes to be aware of:
- 0º- The Equator
- 23.5º N- The Tropic of Cancer
- 23.5º S- The Tropic of Capricorn
- 66.5º N- The Arctic Circle
- 66.5º S- The Antarctic Circle
- 90º N- The North Pole
- 90º S- The South Pole
As you travel north from the equator, in the northern hemisphere, your latitude will increase to 90º N. As you travel south from the equator, in the southern hemisphere, your latitude will increase to 90º S.
Longitude is the angular distance west or east of the Prime Meridian (0º longitude). Longitude lines are vertical, connecting the north and south poles. They are not parallel. Here are some key longitudes to be aware of:
- 0º- The Prime Meridian
- 180º- The International Date Line
As you travel west of the Prime Meridian, in the western hemisphere, your longitude increases to 180º, the International Date Line. As you travel east of the Prime Meridian, in the eastern hemisphere, your longitude increases to 180º, the International Date Line.
In order to pinpoint a location, you must have both the latitude (north or south) and longitude (west or east).
To be more specific about a location, you can use minutes and seconds. Each degree of latitude can be broken into 60 minutes, and each minute can be further broken down into seconds.
