A planet moves in its ellipse so that the line between it and the Sun placed at a focus sweeps out equal areas at equal times.

The square of a planet's orbital period is proportional to the cube of the length of the semi-major axis of its orbit.

The mean distance from the center of the earth to the center of the sun.

The path of the earth around the sun, which is one complete cycle of an orbit, is approximately 365.2425 days in length.

There are two points inside of an ellipse. The sun is one point in our solar system.

Planets revolving around a fixed point, the sun.

Planets revolving around a fixed point, the earth.

The combining of several small nuclei into one large nucleus with the subsequent release of huge amounts of energy.

The splitting of an atom into smaller parts.

Energy that is transferred by electromagnetic radiation, such as light, X-rays, gamma rays, and thermal radiation, which may be described in terms of either discrete packets of energy, called photons, or continuous electromagnetic waves.

The northern lights, one of several astronomical phenomena called polar lights (aurora polaris), are shafts or curtains of colored light visible on occasion in the night sky.

A change in the orientation of the rotational axis of a rotating body.

Is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit.

A periodic oscillation of the earth's axis that causes the precession of the poles to follow a wavy rather than a circular path.

Earth's spin around its own axis. Causes day and night.

The Earth's orbital motion around the sun. Takes 365 days.

A tide just after the first or third quarters of the moon when there is least difference between high and low water.

A tide just after the new or full moon when there is the greatest difference between high and low water.

The orbits of the planets are ellipses with the Sun at one focus, though all except Mercury are very nearly circular.