Earth’s Motions

17.1 Earth-Sun Relationships What are Earth’s major motions? Rotation – Spinning on axis Revolution – Moving around the sun Precession – Wobbling on axis Nutation – Zig-zag motion in the wobbling of axis

Rotation… Click on Globe! Is the turning, or spinning, of the Earth on its axis. Earth rotates at ~ 1000 mph Earth completes one rotation in 24 hours. Rotation is responsible for our days & nights. Click on Globe!

Revolution… Is the motion the Earth along a path around the Sun. Earth revolves at ~ 67,000 mph Earth completes one revolution in 365.25 days Revolution is responsible for our seasons.

What Causes Seasons? First of all… Perihelion is the time when Earth is closest to the sun. Aphelion is the time when Earth is farthest from the sun.

What Causes Seasons? Click on Globe! Seasons are not caused by how far the Earth is from the sun!!! Because the Earth is tilted on its axis. This tilt changes the angle of light which causes the Earth’s seasons. This also changes the length of daylight. Makes no sense without caption in book Click on Globe!

Solstices and Equinoxes Makes no sense without caption in book

17.1 Atmosphere Characteristics Earth-Sun Relationships 17.1 Atmosphere Characteristics  Solstices • The summer solstice is the solstice that occurs on June 21 or 22 in the Northern Hemisphere and is the “official” first day of summer. The winter solstice is the solstice that occurs on December 21 or 22 in the Northern Hemisphere and is the “official” first day of winter.  Equinoxes The autumnal equinox is the equinox that occurs on September 22 or 23 in the Northern Hemisphere. The spring equinox is the equinox that occurs on March 21 or 22 in the Northern Hemisphere.

Precession Animation Is the change in direction in which the axis of the Earth points. This change occurs about every 26,000 years. When this happens, Polaris will no longer be our “North Star”. Instead it will be the star Vega.

Nutation Is a small irregularity in the precession of the Earth This motion is due to the tidal forces created by the moon and the Sun. The Earth’s largest nutation period is about 18.6 years

Barycenter You've heard that Earth revolves around the sun. Well, that's not quite true! In the case of the Earth and the Sun, both bodies orbit around the very center of the mass between them. This point is called the barycenter. Earth and the Sun are "connected" by the gravity pulling them together The larger the planet, the greater the “wobble”

Motions of the Moon Motions of the Earth–Moon System Perigee is the point at which the moon is closest to Earth. Apogee is the point at which the moon is farthest from Earth.

Phases of the Moon The phases are due to the amount of the moon that is lit by the sun. This changes depending on where the moon, Earth, and sun are located. These changes occur monthly. Phases Animation Phases of the Moon YouTube: Song

Lunar Motion  Lunar Rotation YouTube: Synchronized Motion of Moon Why We See The Same Side of The Moon  Lunar Rotation The moon’s rotation and its revolution around Earth are the same rate, 27 1/3 days. This causes the same lunar hemisphere to always face Earth.

22.2 The Earth–Moon–Sun System Eclipses 22.2 The Earth–Moon–Sun System  Solar eclipses occur when the moon moves in a line directly between Earth and the sun, casting a shadow on Earth.  Lunar eclipses occur when the moon passes through Earth’s shadow.

For either eclipse to occur: the moon’s orbit must cross into the plane of the Earth.

Solar Eclipse Makes no sense without caption in book

Solar Eclipse Eclipse’s For 2011 Makes no sense without caption in book Eclipse’s For 2011

Lunar Eclipse Makes no sense without caption in book

Lunar Eclipse Makes no sense without caption in book