The Earth-Moon-Sun SystemChapter 22.2

Celestial Sphere

a model of the sky – an imaginary sphere upon which celestial (“heavenly”) objects are “attached”.

Formation of Solar System

• Inner planets begin to form from metallic and rocky clumps.

Nebular Hypothesis

• Larger outer planets began forming from fragments with a high percentage of ices.

The Nebular Hypothesis

A

C

D

E

B

Motions of Earth

• The main two motions of Earth are rotation and revolution

ROTATION- around earth’s axis

Revolution-around the sun• Perihelion is the time in January when

Earth is closest to the sun

• Aphelion is the time in July when Earth is farthest from the sun

PrecessionEarth has another very slow motion known as precession

A slow motion of Earth’s axis that traces out a cone over a period of 26,000 years

Axis and Seasons • Ecliptic- plane that connects Earth’s orbit with

the celestial sphere.

The angle of the ecliptic is responsible for Earth’s seasons

• Spring Equinox- March 20 or 21 (12 hours of daylight and darkness)

• Autumn Equinox – Sept 22 or 23 (12 hours of daylight and darkness).

• Summer Solstice – June 21 or 22 (15 hours of daylight 9 hours of darkness).

• Winter Solstice- Dec 21 or 22 (9 hours of daylight, 15 hours of darkness)

http://esminfo.prenhall.com/science/geoanimations/animations/01_EarthSun_E2.html

Earth’s natural satellite- The Moon

• Perigee is the point at which the moon is closest to Earth

• Apogee is the point at which the moon is farthest from Earth

Motions of the Earth-Moon System

• The phases of the moon are changes in the way the moon is lit.

• Lunar phases are a result of the motion of the moon and the sunlight that is reflected from its surface– The moon gets bright from the right– Waxing means getting bright– Waning means getting dim

Phases of the Moon

Lunar Motion

• Synodic month- cycle through the moon’s phases (29 ½ days)

• Sidereal Month- The moon’s period of rotation about its axis and its revolution around Earth are the same. (27 1/3 days) – It causes the same lunar hemisphere to

always face Earth

Eclipses• Solar eclipses occur when the moon moves in

a line directly between Earth and the sun, casting a shadow on Earth

• Lunar eclipses occur when the moon passes through Earth’s shadow

• 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

• Usual # of eclipses per year = 4; no more than 7.

Solar Eclipse

Lunar Eclipse

Lunar History

• The 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. The resulting debris was ejected into space, began orbiting around Earth, and eventually united to form the moon.

Formation of Earth’s Moon

Lunar Surface

• Craters- round depression in surface, formed by rapidly moving debris

• Highlands- pitted, light colored areas. Mountain ranges, Far side of moon

• Maria- lava that originated when asteroids hit the surface letting lava flow out

• Regolith- gray debris on surface.