During new and full moon, the earth, moon, and sun are all in the same straight line, but, that during the first and last quarters, they are at right angles. The portions of the earth and moon turned toward the sun are illumined, the shaded portions are in the darkness. To an observer on the earth, the moon, at <em>a</em>, appears new, since the dark part is turned toward the person; at <em>b</em>, however, it must appear full, since the illumined portions are toward the person. At <em>c</em>, and <em>d</em>, the positions of the quarters, only one-half of the illumined half, or one quarter, is seen.

Cause of the Phases of the Moon

During new and full moon, the earth, moon, and sun are all in the same straight line, but, that during…

The Earth in Space.

Earth

The Earth in Space.

Cause of the Curved Shape of the Earth's Orbit.

Earth Orbit

Cause of the Curved Shape of the Earth's Orbit.

If the earth were uniformly covered with a layer of water, the passage of the moon over any place as at <em>a</em>, would cause the water to lose its globular form, become bulged at <em>a</em>, and <em>b</em>, and flattened at <em>c</em>, and <em>d</em>. In other words, the water would become <em>deeper</em> at <em>a</em>, and <em>b</em>, at the parts of the earth nearest and farthest from the moon and <em>shallower</em> in all places 90 degrees or at right angles to these points.

Lunar Tide

If the earth were uniformly covered with a layer of water, the passage of the moon over any place as…

The shape of the earth is that of a round ball or sphere slightly flattened at two opposite sides. Such a body is termed a <em>spheroid</em>. There are two kinds of spheroids-<em>oblate</em> and <em>prolate</em>; the former as the shape of an orange, the latter that of a lemon. The straight line that runs through the centre of a sphere or spheroid and terminates at the circumference is called the <em>diameter</em>. If the sphere rotates-that is, moves around like a top-the diameter on which it turns is called the <em>axis</em>. In the oblate spheroid the axis is the shorter diameter; in the prolate spheroid the axis is the longer diameter.

Oblate and Prolate Spheroid

The shape of the earth is that of a round ball or sphere slightly flattened at two opposite sides. Such…

The celestial bodies that revolve around the sun and receive light and heat from it. This diagram shows the comparative sizes of the planets.

Planets

The celestial bodies that revolve around the sun and receive light and heat from it. This diagram shows…

A diagram showing the planets of our solar system.

Planets

A diagram showing the planets of our solar system.

The flood tides are the highest, and the ebb tides are the lowest. These are called <em>spring tides</em>. They occur twice during every revolution of the moon-once at <em>full</em>, and once at <em>new</em> moon. When the sun and moon are 90 degrees apart, each produces a tide on the portion of the earth directly under it, diminishing somewhat produced by the other body. High tide, then, occurs under the moon, while the high tide caused by the sun, becomes by comparison, a low tide. Such tides are called <em>neap tides</em>.

Positions

The flood tides are the highest, and the ebb tides are the lowest. These are called spring tides.…