Chapter 6: The Sun-Earth-Moon System

SME System

Equator

imaginary line that divides the earth into northern and southern hemispheres

Equinox

day when Earth's axis is not leaning toward or away from the Sun

orbit

The path an object follows as it moves around another object

revolution

motion of an object around another object

Rotation

The spinning motion of a planet on its axis

rotation axis

the line on which an object rotates

solstice

a day when Earth's rotation axis is the most toward or away from the Sun

maria

the large, dark, flat areas on the Moon

phase

the lit part of the Moon or a planet that can be seen from Earth

waning phase

occurs when less of the Moon's near side is lit each night

waxing phase

occurs when more of the Moon's near side is lit each night

lunar eclipse

occurs when the Moon moves into Earth's shadow

penumbra

the lighter part of a shadow where light is partially blocked

solar eclipse

occurs when the Moon's shadow appears on Earth's surface

tide

the daily rise and fall of sea level

umbra

the central, darker part of a shadow where light is totally blocked

neap tide

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

spring tide

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

gibbous moon

when the size of the illuminated portion of the moon is greater than half but not a full moon,
lasts about 6 days can be almost all white or just a little more than 1/2 white