Earth’s Dimensions and Navigation Topic 2.1 Earth’s Dimensions and Navigation

What is the shape of the Earth? spherical Is there any proof?

Evidence for a spherical Earth . . As ships sail away, they disappear from bottom to top. As the sun sets, the last of the light lingers on the top of the trees.

Evidence Continued . . . The North Star is also called Polaris. Polaris is located above the Earth’s North Pole.

So what happens to the altitude of Polaris as you travel north?

Evidence continued . . . The North Star ‘s altitude or height above the horizon changes in a predictable way as latitude changes. As latitude increases, the altitude of Polaris increases.

At the equator, Polaris makes a 0° angle with the horizon. Latitude of Equator = 0°

In Auburn, the altitude of Polaris is 43°. horizon Latitude of Auburn = 43°

At the Arctic Circle, the altitude of Polaris is 66.5°. horizon Latitude of Arctic Circle = 66.5°

At the North Pole, the altitude of Polaris is 90° At the North Pole, the altitude of Polaris is 90°. It is directly overhead. Polaris horizon Latitude of North Pole = 90°

More evidence . . . During a lunar eclipse, the Earth casts a curved shadow. Photos taken from space show a spherical Earth.

Is the Earth a perfect sphere? NO! Earth is an oblate spheroid - slightly flattened at the poles and slightly bulging at the equator.

Evidence for Shape . . . On a true sphere gravity would be the same at all latitudes. But on Earth, gravity varies with latitude. Weight depends on distance from Earth’s center.

Measurements taken by orbiting satellites show that the equatorial diameter is larger than the polar diameter.