22.2 The Earth-Moon- Sun System. Motions of Earth Rotation – turning or spinning of a body on its axis Day & Night 24 hr. time frame Solar Day.

22.2 The Earth-Moon-Sun System

Motions of Earth Rotation – turning or spinning of a body on

its axis Day & Night 24 hr. time frame Solar Day or Sidereal Day

Revolution – motion of a body along a path around some point in space Perihelion – closest to sun (Jan. 3) Aphelion – Farthest from sun (July 4)

Earth’s Axis & Seasons

Axis tilted about 23.5 degrees

Tilted axis = yearly cycle of seasons

Spring Equinox (March 20-21)

Autumn Equinox (September 22-23)

Summer Solstice (June 21-22)

Winter Solstice (December 21-22)

Precession

Slow

Axis traces a circle on the sky

Similar to the wobble of a spinning top

Minor effect on seasons b/c the angle of tilt changes only slightly

Earth-Sun Motion

Sun revolves around the galaxy

Trip takes 230 million years to traverse at speeds approaching 250 km per second

Galaxies themselves are also in motion

Motions of the Earth-Moon System

Moon orbits Earth in about a month’s time

Perigee – moon is closest to Earth

Apogee – Moon is farthest from Earth

Constantly change the relative positions of the sun, Earth, and Moon

Phases of the Moon Monthly

Crescent Phase

Waxing

First-quarter phase

Full Moon phase

Waning

New-moon phase

Lunar phases are a result of the motion of the moon & the sunlight that is reflected from its surface

pg. 626 Fig. 15 A & B

Lunar Motions

Cycle requires 29 ½ days = moon cycle = synodic month

Basis for the Roman calendar

Moon’s revolution around Earth & not the true period which only takes 27 1/3 days = sidereal month

Moon’s period of rotation on its axis & its revolution around Earth are the same

Eclipses

Shadow effects

When the moon moves in a line directly btw Earth & Sun it casts a dark shadow on Earth = Solar Eclipse

Moon is eclipsed when it moves within Earth’s shadow = Lunar Eclipse

During a new-moon or full-moon phase, the moon’s orbit must cross the plane of the ecliptic for an eclipse to take place

Usually 4 eclipses (in sets)

REVIEW REVIEW REVIEW

Why don’t eclipses occur during every full-moon or new-moon phase?

In what ways does Earth move?

What causes the phases of the moon?

Describe the locations of the sun, moon, & Earth during a solar eclipse & during a lunar eclipse.

22.3 Earth’s Moon

The Lunar Surface

Moon has no atmosphere or water

Erosion occurs b/c the lack of a protective atmosphere

Most obvious structures are craters (round depressions in the surface)

Produced mainly by the impact of rapidly moving debris

The heat generated by the impact is enough to melt rock

Continued… Most of lunar surface is made up of densely

pitted, light-colored areas = Highlands

Within the highland regions are mountain ranges

Dark relatively smooth area on the moon’s surface = Mare

Maria, ancient beds of basaltic lava, originated when asteroids punctured the lunar surface, letting magma bleed out.

Long channels that are associated with maria = Rilles

Continued…

All lunar terrains are mantled with a layer of gray debris derived from a few billion years of bombardment from meteorites = lunar regolith

Composed of igneous rocks, glass beads, & fine lunar dust

Lunar History

Moon is our nearest planetary neighbor

Most widely accepted model for the origin of the moon is that when the solar system was forming, a body the size of Mars impacted Earth

Impact would have liquefied Earth’s surface & ejected huge amounts of crustal & mantle rock from an infant Earth

A portion of this ejected debris would have entered an orbit around Earth where it combined to form the moon

REVIEW REVIEW REVIEW

How do craters form?

How did maria originate?

What are the stages that formed the moon?