MOTIONS OF EARTHMOTIONS OF EARTH

CHAPTER 20CHAPTER 20

ROTATIONROTATION Time for a planet to Time for a planet to

make one spin on it’s make one spin on it’s axisaxis

Equal to planet’s DAYEqual to planet’s DAY

Which way does Which way does Earth rotate?Earth rotate?

Solar day- 24 hoursSolar day- 24 hoursCompared to the sunCompared to the sun

Sidereal Day- 23h 56m 4.09sSidereal Day- 23h 56m 4.09sCompared to distant starsCompared to distant starsTrue rotationTrue rotation

REVOLUTIONREVOLUTION Time for planet to revolve around it’s star (orbit)Time for planet to revolve around it’s star (orbit) YEARYEAR

Earth= 365.25 daysEarth= 365.25 days

Perihelion= closest to sunPerihelion= closest to sun Jan. 3Jan. 3

Aphelion= farthest from sunAphelion= farthest from sun July 4July 4

Kepler’s Law (#2)Kepler’s Law (#2) Law of equal areasLaw of equal areas Speed of planet’s Speed of planet’s

revolution varies revolution varies based on distance based on distance from sunfrom sun

When fastest?When fastest? Closer (perihelion)Closer (perihelion)

PrecessionPrecession Movement in the Movement in the directiondirection of Earth’s axis of Earth’s axis Today; axis points towards PolarisToday; axis points towards Polaris In 12,000 years; axis points toward VegaIn 12,000 years; axis points toward Vega

PrecessionPrecession

GALAXY MOTIONGALAXY MOTION ROTATIONROTATION 230 million years for 230 million years for

Milky Way to rotateMilky Way to rotate 150 miles/sec150 miles/sec

Galaxy expansionGalaxy expansion

That’s a lot of motion!That’s a lot of motion! RotationRotation RevolutionRevolution PrecessionPrecession Galaxy rotationGalaxy rotation GalaxyexpansionGalaxyexpansion

I’M DIZZY!I’M DIZZY!

MOON MOTIONSMOON MOTIONS Revolves around Revolves around

EarthEarth

Revolution= 29.5 Revolution= 29.5 daysdays

(sideral= 27.3 days)(sideral= 27.3 days)

MoonMoon Perigee- moon Perigee- moon

closest to earthclosest to earth

Apogee- moon Apogee- moon farthest from earthfarthest from earth

Moon CalendarMoon Calendar