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MOTIONS OF THE EARTH, THE MOON, AND PLANETS Earth’s Movement Rotation Revolution The spinning of an object The movement of one around an axis. Example: - The Earth completes a full rotation in 24 hours 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 MOON Eclipses Solar Eclipse Lunar Eclipse A solar eclipse occurs when A lunar eclipse occurs when the Moon passes between the Sun and the Earth. 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 (87-150 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 (1473-1543) 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 (1564-1642) 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 23.5ᵒ 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 21st) Winter Solstice: shortest day (December 21st) Vernal Equinox: first day of Spring with 12hour days and 12 hour nights (March 21st) Autumnal Equinox: first day of Autumn with 12 hour days and 12 hour nights (September 21st) Precession: Earth’s Wobble The Earth spins around an axis that wobbles like a slow spinning top. This wobble takes 26 000 years to complete. Currently, the North Star is Polaris. In 12 000 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