Earth’s Movement RotationRevolution  The spinning of an object around an axis. Example: - The Earth completes a full rotation in 24 hours  The movement of one object around another (aka orbit) Example: - The Earth completes a full revolution around the Sun in ~ 365 days.

Orbital Radius and Eccentricity  Planets and other celestial objects rarely follow perfect circular paths.  The orbital radius refers to the average distance between the Sun and the celestial object of interest

Orbital Radius and Eccentricity  Highly oval, or elliptical, orbits are called eccentric orbits

Motions of the Moon  The Moon exhibits synchronous rotation  Its rotational period is the same as its revolution.  This means the same side of the Moon is always facing Earth

Phases of the Moon  The Moon reflects the Sun’s light as the Earth revolves around the Sun and the Moon revolves around the Earth.

MOON

Eclipses Solar EclipseLunar Eclipse  A solar eclipse occurs when the Moon passes between the Sun and the Earth.  A lunar eclipse occurs when the Earth passes between the Sun and the Moon

Force of Gravity  A natural phenomenon by which physical bodies attract with a force proportional to their mass.

The Moon’s Influence on Earth’s Tides  The Moon’s gravity pulls Earth and its oceans toward it.  This causes a bulge of water to form on the side of the Earth facing the Moon.

How Do We Know What We Know?  Claudius Ptolemy ( BCE)  Roman citizen living in Egypt  Mathematician, Astronomer, Geographer, Astrologer and Poet  Created the Geocentric Model of the Solar System  The Earth is the center of the Solar System

How Do We Know What We Know?  Nicholas Copernicus ( )  Renaissance Astronomer from Poland  Created the Heliocentric Model of the Solar System but kept his views to himself and close friends.  The Sun is at the center of the Solar System

How Do We Know What We Know?  Galileo Galilei ( )  Italian physicist, mathematician, astronomer, and philosopher  “The Father of Modern Physics”  Found support for the Heliocentric Model of the Solar System and defended the Copernican view of the Solar System.

Earth’s Tilt and the Seasons  The Earth rotates at a 23.5 angle from the Earth-Sun orbital plane.  This tilt is the cause of seasons.

Seasons in the Northern Hemisphere  When the Earth is tilted towards the Sun, North America experiences summer.

Seasons in the Northern Hemisphere  When the Earth is tilted away from the Sun, North American experiences winter.

Seasons in the Northern Hemisphere  When the Earth isn’t tilted towards, or away from, the Sun, North America experiences Autumn and Spring.

Solstices and Equinoxes in the Northern Hemisphere  Summer Solstice: longest day (June 21 st )  Winter Solstice: shortest day (December 21 st )  Vernal Equinox: first day of Spring with 12hour days and 12 hour nights (March 21 st )  Autumnal Equinox: first day of Autumn with 12 hour days and 12 hour nights (September 21 st )

Precession: Earth’s Wobble  The Earth spins around an axis that wobbles like a slow spinning top.  This wobble takes years to complete.  Currently, the North Star is Polaris. In years the new “North Star” will be the star Vega.

Homework  Finish P. 328 Q: 1-14  Read 8.6 in preparation for tomorrow’s class