Day
the time required for the Earth to complete one revolution around its axis
Sidereal Day
the time required for one complete rotation of the Earth in reference to a star, 23 hours, 56 minutes, and 4.09 seconds
Year
the time required for the earth to complete one revolution around the Sun
Axis
the imaginary line through the north and south poles on which the Earth rotates.
Equatorial Bulge
an oblate bulge that the Earth has due to centrifugal force from the Earth’s rotation.
Ellipse
the point in the Earth’s revolution when it is farthest to the sun.
Perihelion
the point in the Earth’s revolution when it is closest to the sun.
Aphelion
the point in the Earth’s revolution when it is farthest to the sun.
Orbit
the path a planet takes around the sun.
Eccentricity
the ratio of the distance from the center of the ellipse to a focus relative to the semi-major axis.