Bellwork 9/17 What causes the seasons? What causes the phases of the moon? What causes a solar and/or lunar eclipse?

Let’s begin to look at ourselves in this vast expanse of space…

Understanding our Perspective from Earth Seasons Lunar Phases Eclipses

Earth-Moon-Sun System Two primary motions: Rotation: turning or spinning of a body on its axis Revolution: the motion of a body (such as a planet or moon) along a path around some point in space. *Both the moon and the Earth rotate & revolve

Earth-Sun System Earth’s revolution is NOT circular…

Earth-Sun System What causes the seasons? The tilt of Earth’s axis toward and away from the sun as the planet revolves around the sun

Other Earth Motions… Precession Very slow Earth movement “wobbling top” Direction in which Earth's axis points continually changes Movement with the solar system in the direction of the star Vega Revolution with the Sun around the galaxy Movement with the galaxy within the universe

Precession of Earth

Modeling Lab Explore the concepts of Lunar Phases and Eclipses Rework misconceptions Form concrete ideas through modeling …yes…I will give you the “official” definitions & explanations later, but I want you to grapple with your own understanding first!!

Earth-Moon system Moon Phases The relative positions of the Sun, Earth, and Moon constantly change Lunar phases are a consequence of the motion of the Moon and the sunlight that is reflected from its surface It’s because of our perspective from Earth…what we can see at any given time… This is NOT Earth’s shadow!

Lunar motions Moon's period of rotation about its axis and its revolution around Earth are the same Causes the same lunar hemisphere to always face Earth Synodic month Cycle of the moon phases Takes 29 1/2 days

“To obscure light from” Eclipses “To obscure light from” Solar eclipse Moon moves in a line directly between Earth and the Sun Can only occur during the new-Moon phase Lunar eclipse Moon moves within the shadow of Earth Only occurs during the full-Moon phase **For any eclipse to take place, the Moon must be in the plane of the ecliptic at the time of new- or full-Moon **

Solar eclipse

Lunar eclipse

Modeling lab:

Why don’t we have an eclipse every month?? Because the Moon's orbit is inclined about 5 degrees to the plane of the ecliptic, during most of the times of new- and full-Moon the Moon is above or below the plane, and no eclipse can occur The usual number of eclipses is four per year

Why does a Lunar Eclipse Appear Red? If the Earth had no atmosphere, the moon would appear invisible But, the reflected light from the moon travels through our atmosphere

Why does the moon appear red/orange sometimes? Our atmosphere! When the moon is closer to the horizon, the light it reflects must pass through more of the atmosphere More atmosphere = longer wavelength