Chapter 22 Section 2

Rotation vs. Revolution Rotation: The turning of a body on its axis Revolution: The motion of a body along a path around some body in space

Precession The slight wobbling movement of Earth as it rotates on its axis Precession takes about 26,000 years to complete Reminder: View precession in Starry Night: Favorites>Guides>Precession

Rotation The Earth rotates 360° in 23 Hours, 56 Minutes, 4 seconds The sun appears directly overhead (noon) in exactly 24 hours How is this possible?

Mean Solar Day vs. Sidereal Day The Earth rotates and revolves at the same time. The angular shift caused by the revolution is equal to the missing 4 minutes!

Revolution The Earth moves around the sun at 107,000 kph! Earths orbit around the sun is elliptical and averages 93 million miles Earth makes one revolution around the sun in 365.25636042 days Reminder: View the leap year in starry night! Favorites>solar system>inner planets>inner solar system Zoom into earth and manually advance 1 year at a time Revolution

Perihelion Occurs when Earth is closest to the sun (January 3rd) (winter!) Aphelion Occurs when Earth is furthest away from the sun (July 4th) (summer!)

Earth’s Tilt Creates the Seasons The inclination of Earth’s hemispheres either toward or away from the sun creates the seasons, not our distance from the sun! Earth’s Tilt Creates the Seasons

The path that the sun appears to follow throughout the year against the background stars The planets and moon orbit in basically the same plane and therefore also follow the ecliptic Reminder: View the ecliptic in Starry Night and trace the motion of the sun 1) Options(side menu)>Guides>Ecliptic>Equator Turn on constellation stick figures and labels 2) Favorites>Guides>Ecliptic grid 3) Favorites>Guides>Atlas Ecliptic

More Movement! The Earth Rotates on it’s axis and revolves around the sun, but: The solar system is screaming toward Vega (a bright star in the constellation Lyra, about 25 ly from Earth) at 20 Kilometers per SECOND! The solar system is orbiting the galactic center at about 250 Kilometers per SECOND!! This trip will take 230 million years!

Da Moon The moon orbits Earth in an elliptical orbit, meaning its distance can vary by as much as 6%

Perigee Apogee Occurs when moon is furthest away from the Earth Occurs when the moon is closest to the Earth Apogee Occurs when moon is furthest away from the Earth

Lunar Phases As the moon orbits Earth, the sun shines on it from different angles, creating lunar phases

Lunar Phases The bright part of the moon is caused by sunlight reflecting off of the surface The dark part is the moons own shadow… it is not the shadow of Earth!

Phase Facts It takes the 29.5 days for the moon to complete one cycle The earliest calendars were based on the phases of the moon, contained 13 months, and occasionally needed to insert an entire “leap month” to account for the difference

Weird Science The rotation of the moon on its axis exactly matches it revolution speed which means the same side of the moon always faces Earth! Reminder explore moon phases in Starry Night A day on the moon lasts 2 weeks This, and no atmosphere, allows surfaces temperatures to reach 260° F! Night temperature reaches -343° F!

Lunar Eclipse A lunar eclipse occurs when the Earth, Moon, and Sun line up, causing the Earth to cast a shadow on the moon

Total Lunar Eclipse This eclipse was captured in Murrieta just before dawn on 12/10/2011

Solar Eclipse A solar eclipse occurs when the Earth, Moon, and Sun line up, causing the moon to cast a shadow on the Earth Because the moon is so small, the shadow can only be seen from a small area on the surface of the Earth.

Solar Eclipse

Eclipse Because the moon orbits Earth on a slight incline compared to the orbit of Earth around the sun, an eclipse only occurs about twice a year. If the incline did not exist, we would have a solar and lunar eclipse every month!