7th Grade Unit 5 Lessons 1 & 2 combined set

axis

An imaginary line that passes through Earth's center and the North and South poles, about which Earth rotates

rotation

The spinning motion of an object on its axis

day

the time required for a planet to rotate once on its axis

revolution

the movement of one object around another

year

the time required for a planet to orbit once around the sun

midnight sun

continuous daylight, a time when the sun is visible at midnight during the summer in either the Arctic or Antarctic Circle

polar night

the extended time in winter at places close to the North or South Pole, when the sun does not appear above the horizon

season

A period of the year characterized by particular conditions of temperature and other weather trends

equinox

Each of the two times of the year when days and nights are of equal length

solstice

The two days of the year on which the sun reaches its greatest distance north or south of the equator; sunlight is at a maximum in one hemisphere and a minimum in the other hemisphere

satellite

An object that orbits a larger object in space

orbit

The path of an object as it revolves around another object in space

moon

A natural satellite that revolves around a planet

gravity

A force of attraction between objects that is due to their masses

lunar phases

Changes in the visible portion of the Moon caused by its revolution about the Earth allowing us to see more or less of its lit up visible portion

waxing

describes phases following a new moon, as more of the Moon's lighted side becomes visible from Earth

waning

describes phases following a full moon, as less of the Moon's lighted side is visible from Earth

full moon

phase that occurs when all of the Moon's surface facing Earth reflects light

new moon

Moon phase that occurs when the Moon is between Earth and the Sun, at which point the Moon cannot be seen because its lighted half is facing the Sun and its dark side faces Earth

eclipse

an event in which one object in space casts a shadow onto another object

lunar eclipse

an eclipse in which the moon appears darkened as it passes into the earth's shadow; Earth is between the Sun and Moon

umbra

The darkest part of a shadow

penumbra

the lighter part of a shadow where light only is partially blocked

solar eclipse

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