Unit 9: Earth Cycles

Vocabulary

AxisImaginary line about which an object rotates.

RotateTo turn or cause to turn about an axis or a center.

RevolveTo move in an orbit.

CounterclockwiseIn a direction opposite to that in which the hands of a clock rotate.

Rotational AxisThe Earth is rotating around an imaginary axis at a 23.5° tilt. It points in the same direction relative to the stars, so that the North Pole points towards the star Polaris (North Star).

Vernal EquinoxEarth reaches a point where the tilt is not toward

or away from the Sun, and the lengths of day and night are the same all over Earth. March

21st.

Summer SolsticeEarth’s northern hemisphere is tilted toward the Sun

and days become longer and warmer. June 21st.

Autumnal EquinoxEarth reaches a point where the tilt is not toward or away from the Sun, and the lengths of day and night are the same all over Earth. September 22nd.

Winter SolsticeEarth reaches a point when the northern hemisphere is tilted away from the sun and the hours of daylight are the shortest. December 21st.

EclipseThe partial or complete hiding from view

of an astronomical object, such as the Sun or Moon, when another astronomical

object comes between it and the observer.

Solar EclipseWhen the Moon blocks the Sun or a part of it.

Lunar EclipseWhen the Earth casts a shadow on the Moon.

New MoonWhen the Moon is between the Earth and the Sun; the illuminated portion is on the backside we can’t see.

Waxing CrescentDuring this phase, part of the Moon is beginning to show. We say that the Moon is "waxing" because each night a little bit more is visible for a little bit longer.

First Quarter MoonComes a week after new moon; rises at noon and is high overhead at sunset, then sets around midnight.

Waxing GibbousWhen most of the Moon is visible we say it is a

Gibbous Moon. During this phase, the Moon remains in the sky most of the night.

Full MoonWhen we can observe the entire face of the Moon, we call it a Full Moon. The Moon is opposite the Earth and the Sun.

Waning GibbousInstead of seeing more of the Moon each night, we begin to see less and less of the Moon each night. This is what the word "waning" means.

Third Quarter MoonComes about three weeks after new moon; rises around midnight, appears at its highest in the sky around dawn, and sets at noon.

Waning CrescentEach night less of the Moon is visible for less

time.

Gravitational AttractionForce of attraction between all masses in the universe, especially

the attraction of the Earth’s mass for bodies near its surface.

Neap TidesTides that are the least extreme; happen twice a month, at first and last quarter moon phases.

Spring TidesTides that are most extreme; occur twice a month, at full and new moon phases.

High TideThe tide when the water is at its greatest

height.

Low TideThe tide at its lowest level at a particular

time and place.