Moon Notes Day 3 Chapter 3

3-1 The changeable moon The moon appears to us to move eastward The markings on the surface of the moon do not seem to change ◦(we seem to be looking at the same part of the surface every time we see the moon).

Watch the moon on a clear night. In just one hour, you can see the moon move eastward against the background of the stars. As the moon follows its orbit, it moves about 13 degrees in angular diameter (through its orbit). Each night the moon is about 13 degrees eastward of its previous location. This is the result of the moon along its orbit around Earth.

The Cycle of Phases We have examined the phases of the moon. Recall: 8 phases with names and appearance (be able to draw and label) The moon has a 28 day cycle as it orbits Earth The moon does NOT generate light, it reflects sunlight. The shapes of the phases describe the shape we see, that is reflecting light at that time in the moon’s orbit.

3-2 The Tides Tides are periodic changes in the ocean caused by the moon’s gravity. The Earth’s gravity is much greater than the moons, but the moon is large enough to have a significant gravitational effect on the Earth.

Moon gravity is % of Earth gravity This small amount is enough to cause tides. Tides are produced by a DIFFERENCE between the gravitational force acting on different parts of Earth. When one side of Earth is facing the moon, the moon is closer to that side. The moon’s gravity pulls more strongly on the oceans on the nearest side.

The moon’s gravity pulls more strongly on the oceans on the near side of Earth, than on Earth’s center. This DIFFERENCE in pull is small However, it is enough to make the ocean waters flow into a bulge on the side of Earth facing the moon. A bulge also forms on the side of the Earth facing away from the moon. ◦The far side is about 6400 km farther from the moon, than Earth’s center. ◦The moons gravity pulls less strongly, and the ocean bulges away from the moon.

Fig 3-2 a & b

The tidal bulges remain fixed along the Earth-moon line. Earth is rotating on its axis, so the area on Earth affected, changes. As the Earth rotates, a new area is carried into the tidal bulge. Technically speaking, the tide does not “come in “, we “go into the tide”.

Spring Tides The sun affects tides on Earth too; less than the moon. At new moon and full moon, the moon and Sun produce tidal bulges that work together to produce extreme tidal changes. These are called Spring Tides.

Neap Tides Neap tides occur at first quarter and third quarter moons. The moon and the Sun pull at right angles to each other. The smaller tide caused by the Sun, reduces the tide caused by the moon.

A. Spring Tide B. Neap Tide