Chapter 22.2 The Earth- Moon-Sun System Chapter 22.3: Earth s Moon
Chapter 22.2 The Earth- Moon-Sun System
Motions of the Earth The two main motions of the Earth are rotation and revolution Rotation is the turning or spinning of a body on its axis Revolution is the motion of a body, such as a planet or moon, along a path around some point in space.
Motions of the Earth Precession the slight movement of the Earth s axis over a period of 26,000 years.
Rotation Produces day and night The mean solar day is the time from one noon until the next ~ 24 hours Noon occurs when the sun reaches the zenith highest point in the sky Not the same as the sidereal day
Revolution The Earth revolves at a speed of 107,000 kilometers per hour (66,000mph) Perihelion when Earth is closest to the sun Aphelion when Earth is farthest from the sun Average distance ~ 93 million miles
Revolution The apparent annual path of the sun against the backdrop of the celestial sphere is called the ecliptic
Earth s Axis and Seasons The Earth is tilted 23.5 degrees this is why we have the seasons When is Summer? June 21 or 22 When is Winter? December 21 or 22 When is Spring? March 20 or 21 When is Fall? September 22 or 23
Precession The direction in which the axis of the Earth points changes direction very slowly. It traces out a circle The period of precession is 26,000 years.
Earth-Sun Motion The entire solar system is moving at 20 kilometers per second toward Vega The sun and solar system is revolving around the center of the galaxy at 250 kilometers per second The entire galaxy is also moving toward the Great Galaxy in Andromeda
Motions of the Earth/Moon The moon rotates counter-clockwise when viewed from above the North Pole The average distance from the earth to the moon is 384,401 Km (238,867miles) The moon is closest to the earth at a point called perigee The moon is farthest from the earth at a point called apogee
Phases of the Moon Lunar phases are a result of the motions of the moon and the sunlight that is reflected from its surface. Half of the moon is illuminated at all times.
Lunar Motions The cycle of the moon (apparent motion) through its phases requires 29.5 days, a time span called the synodic month The actual, true period of revolution for the moon around the earth is 27.3 days, a time span called the sidereal month.
Temperature on the Moon The lit side has a temperature of approximately 127 degrees Celsius (260 degrees Fahrenheit) The dark side has a temperature of approximately 173 degrees Celsius (-279 degrees Fahrenheit)
Eclipses Eclipses are shadow effects Usually four each year, occasionally,up to seven Solar Eclipse the moon moves in a direct line between the Earth and the sun Lunar Eclipse the earth moves in a direct line between the Sun and the Moon
Lunar Eclipse Occurs during the Full Moon phase Moon looks like a copper color Lasts up to four hours Can be seen by everyone on the side of Earth facing the moon
Solar Eclipse Occurs during the New Moon phase The shadow casts on the Earth is about the size of South Carolina Can last up to seven minutes If in the umbra, you see totality If in the penumbra, you see a partial solar eclipse
Annular Solar Eclipse Occur when a region on the Earth's surface is in line with the umbra, but the distances are such that the tip of the umbra does not reach the Earth's surface.
22.3 Earth s Moon The moon is about ¼ the size of the Earth The moon s gravity is 1/6 th that of the Earth
The Lunar Surface Dark regions are called Maria Most obvious feature are the craters Splash marks that radiate outwards from craters are called rays The light colored regions on the moon are highlands
The Lunar Surface Large channels associated with maria are called rilles, which are probably the remnants of ancient lava flows The moon has a soil-like layer called lunar regolith
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 debris from the impact formed the moon.