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the center around which something rotates


the act of rotating as if on an axis


the movement of an object around another object


the path described by one celestial body in its revolution about another


either of the two times of the year when the sun is at its greatest distance from the celestial equator


either of two times of the year when the sun crosses the plane of the earth's equator and day and night are of equal length

Phases of the moon

the progression of changes in the moon's appearance during the month

New moon

the time at which the moon appears as a narrow waxing crescent

crescent moon

the phase of the moon in which only a curved edge of the moon's side that faced earth is illuminated

Gibbous moon

when the size of the illuminated portion of the moon is greater than half but not a full moon

full moon

the time when the moon is fully illuminated


a gradual decrease in magnitude or extent


pertaining to the period during which the visible surface of the moon increases

solar eclipse

occurs when the Moon passes directly between the Sun and Earth and casts a shadow over part of Earth

lunar eclipse

the blocking of sunlight to the moon that occurs when Earth is directly between the sun and the moon


a region of complete shadow resulting from total obstruction of light


a fringe region of partial shadow around an umbra

total eclipse

an eclipse as seen from a place where the eclipsed body is completely obscured

partial eclipse

an eclipse in which the eclipsed body is only partially obscured


an immense cloud of gas (mainly hydrogen) and dust in interstellar space


the force of attraction between all masses in the universe

Nuclear fusion

a nuclear reaction in which nuclei combine to form more massive nuclei with the simultaneous release of energy


All matter and energy that exists in space

big bang

the cosmic explosion that is hypothesized to have marked the origin of the universe

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