Do Now: 1) What are the 3 spheres of Earth? 2) Which layer is most dense? 3) We are known as the _____ planet because we are covered by 71% of water.

Measuring the Earth Aim: Is Earth really a perfect sphere?

How do we know that Earth is spherical?

1. Satellite images – we can now take photos of Earth from space, seeing its true shape. 1. Satellite images – we can now take photos of Earth from space, seeing its true shape. Picture from the Apollo Mission

2. Sailing Ships - Watching ships “disappear” over the horizon 2. Sailing Ships - Watching ships “disappear” over the horizon Cont’d

Cont’d 3. Lunar Eclipse 3. Lunar Eclipse Earth casts a slightly rounded shadow on the MoonEarth casts a slightly rounded shadow on the Moon

4. Polaris – (the North Star) 4. Polaris – (the North Star) As you move along the same line of latitude, Polaris’ altitude stays the same, but as you move along a line of longitude, Polaris’ altitude changesAs you move along the same line of latitude, Polaris’ altitude stays the same, but as you move along a line of longitude, Polaris’ altitude changes *Polaris’ altitude = your Northern latitude

Polaris

Ursa Major and Ursa Minor

Finding Locations Using Polaris Sextant - instrument for measuring the altitude of the sun or another celestial body Sextant - instrument for measuring the altitude of the sun or another celestial body Parts Includes:Parts Includes: Telescope - locating the North Star Telescope - locating the North Star Protractor - finding the altitude (= latitude) Protractor - finding the altitude (= latitude) Measurements can then be used to determine the observer's geographical position Measurements can then be used to determine the observer's geographical position

Sextant

Is Earth a PERFECT sphere?

What shape is the Earth? Earth is considered to be an Oblate Spheroid. Earth is considered to be an Oblate Spheroid. This means that Earth is slightly flattened at the poles and slightly bulging at the equator. This means that Earth is slightly flattened at the poles and slightly bulging at the equator. Because of the rotation – matterBecause of the rotation – matter “bunches” in the middle “bunches” in the middle

How big is Earth? Polar Diameter = Polar Diameter = 12,714 km 12,714 km Equatorial Diameter = Equatorial Diameter = 12,756 km 12,756 km

The Earth is only slightly oblate, so it appears to be spherical!

How does this affect gravity? 5. Gravity Measures – 5. Gravity Measures – the closer to Earth’s core (center), the more gravitational pull, the more an object weighs.

Weight and Gravity Equator - the Earth's diameter is greatest; objects weigh a little less.Equator - the Earth's diameter is greatest; objects weigh a little less. Poles - the Earth's diameter is the least, objects weight a little more.Poles - the Earth's diameter is the least, objects weight a little more.

Closure Questions: 1) The Earth’s shape most closely resembles which of the following objects? (a) a football(c) a ping-pong ball (b) a pear(d) an apple

2) The true shape of the Earth is best described as a: (a) perfect sphere (b) slightly oblate sphere (c) perfect ellipse (d) highly eccentric ellipse

3) An observer watching a sailing ship notes that it appears to be “sinking” as it moves away. This observation proved that: (a) the surface of the ocean has depressions (b) the earth is rotating (c) the earth is revolving (d) the earth has a curved surface