MOTIONS OF EARTH CHAPTER 20

ROTATION Time for a planet to make one spin on it’s axis Time for a planet to make one spin on it’s axis Equal to planet’s DAY Equal to planet’s DAY Which way does Earth rotate? Which way does Earth rotate?

Solar day- 24 hours Solar day- 24 hours Compared to the sun Compared to the sun Sidereal Day- 23h 56m 4.09s Sidereal Day- 23h 56m 4.09s Compared to distant stars Compared to distant stars True rotation True rotation

REVOLUTION Time for planet to revolve around it’s star (orbit) Time for planet to revolve around it’s star (orbit) YEAR YEAR Earth= days Earth= days Perihelion= closest to sun Perihelion= closest to sun Jan. 3 Jan. 3 Aphelion= farthest from sun Aphelion= farthest from sun July 4 July 4

Kepler’s Law (#2) Law of equal areas Law of equal areas Speed of planet’s revolution varies based on distance from sun Speed of planet’s revolution varies based on distance from sun When fastest? When fastest? Closer (perihelion) Closer (perihelion)

Precession Movement in the direction of Earth’s axis Movement in the direction of Earth’s axis Today; axis points towards Polaris Today; axis points towards Polaris In 12,000 years; axis points toward Vega In 12,000 years; axis points toward Vega

Precession

GALAXY MOTION ROTATION ROTATION 230 million years for Milky Way to rotate 230 million years for Milky Way to rotate 150 miles/sec 150 miles/sec

Galaxy expansion

That’s a lot of motion! Rotation Rotation Revolution Revolution Precession Precession Galaxy rotation Galaxy rotation Galaxyexpansion Galaxyexpansion I’M DIZZY! I’M DIZZY!

MOON MOTIONS Revolves around Earth Revolves around Earth Revolution= 29.5 days Revolution= 29.5 days (sideral= 27.3 days) (sideral= 27.3 days)

Moon Perigee- moon closest to earth Perigee- moon closest to earth Apogee- moon farthest from earth Apogee- moon farthest from earth

Moon Calendar