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Any of the celestial bodies (other than comets or satellites) that revolve around the sun in the solar system


The elongated, closed curve that describes Earth's yearlong orbit around the Sun


The point of geometric significance. One of two point sused to define an ellipse. (plural: foci)


The point at which the earth is closest to the sun.


The place in the Earth's orbit where Earth is farthest away from the sun.

astronomical unit

The average distance from Earth to the Sun, approximately 150 million kilometers


The fraction or percentage of light shining on a planet or other nonluminous celestial object that it reflects


Amount of matter in an object.( not dependent on the force of gravity)


A measure of the force of gravity exerted on an object

surface gravity

The downward pull (gravitational force) a celestial body exerts on objects at its surface

inferior planet

A planet that orbits between the Earth and the Sun. Mercury and Venus are the only two inferior planets in our solar system.

superior planet

The planets whose orbits are farther from the sun than the earth's orbit


One of the different apparent shapes of the moon as seen from earth.


When a planet passes directly between the earth and the sun so that we see its dark silhouette against the sun's bright disk

retrograde motion

The apparent backward motion of a planet compared to other objects in the solar system

terrestrial planet

Planets that are similar to Earth in density and size


Jupiter like; the four outer planets: Jupiter, Saturn, Uranus, Neptune; large/gaseous with rocky cores and low densities.

gas giant

A large planet that consists mostly of gases in a dense form. The four large planets in the outer solar system- Jupiter, Saturn, Uranus, and Neptune.

Galilean moons

The name given to Jupiter's four largest moons, Io, Europa, Callisto & Ganymede. They were discovered by Galileo Galilei.

Great Red Spot

A giant, high-pressure continuous storm on Jupiter. It is reddish, oval shaped, and rotates.

Cassini's Division

Large gap between the two largest rings of Saturn caused by the gravitational pull of the moon Mimas


To hide or to eclipse; to cross in front of

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