26.2 Movements of Earth26.2 Movements of Earth

The Rotating EarthThe Rotating Earth

The Spinning of Earth on its axis is called The Spinning of Earth on its axis is called ROTATIONROTATION..

How long does each rotation take?How long does each rotation take?One DayOne Day

Earth rotates from West to East, sun appears to Earth rotates from West to East, sun appears to rise in the east in the morning, cross the sky, and rise in the east in the morning, cross the sky, and set in the west.set in the west.

Foucault PendulumFoucault Pendulum

1919thth centruy, Jean-Bernard-Leon Foucault centruy, Jean-Bernard-Leon FoucaultProvided evidence of Earth’s rotationProvided evidence of Earth’s rotationObserved that the path of the pendulum Observed that the path of the pendulum

appeared to change over time…appeared to change over time…BUT, it was the floor that was moving BUT, it was the floor that was moving

while the pendulum’s path stayed while the pendulum’s path stayed constant.constant.

Because the floor was attached to the Because the floor was attached to the Earth, he concluded that the Earth rotatesEarth, he concluded that the Earth rotates

Foucault Foucault

Pendulum in Pendulum in

ParisParis

http://http://www.fi.edu/time/Journey/Pendulum/tfi_pendulum.html

The Coriolis EffectThe Coriolis Effect

Evidence of the Earth’s rotationEvidence of the Earth’s rotation Observations in ocean surface currents and Observations in ocean surface currents and

wind belts.wind belts. Earth’s rotation causes ocean currents and wind Earth’s rotation causes ocean currents and wind

belts to be deflected to the right in the Northern belts to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere and to the left in the Southern HemisphereHemisphere

This curving/deflection of wind and ocean This curving/deflection of wind and ocean currents caused by Earth’s rotation is called the currents caused by Earth’s rotation is called the Coriolis effect.Coriolis effect.

Revolving EarthRevolving Earth

Earth travels around the sun at an average Earth travels around the sun at an average speed of 29.8 km/sspeed of 29.8 km/s

The motion of a body that travels around The motion of a body that travels around another body in space is called a another body in space is called a RevolutionRevolution

How long is one complete revolution of How long is one complete revolution of Earth?Earth?365 ¼ days365 ¼ days

Earth’s OrbitEarth’s Orbit

Orbit: path that a body follows as it travels Orbit: path that a body follows as it travels around another body in spacearound another body in space

What do you think the Earth’s orbit around the What do you think the Earth’s orbit around the sun looks like?sun looks like?

Earth’s orbit is an ellipse (“oval”) Earth’s orbit is an ellipse (“oval”) Earth is not Earth is not always the same distance from the sun.always the same distance from the sun.

Perihelion: point in orbit when Earth is closest to Perihelion: point in orbit when Earth is closest to sun sun

Aphelion: point in orbit when Earth is furthest Aphelion: point in orbit when Earth is furthest from sun from sun

Constellations and Earth’s motionConstellations and Earth’s motion

Evidence of Earth’s revolution and rotation can Evidence of Earth’s revolution and rotation can be seen in the motion of constellationsbe seen in the motion of constellations.. Stars appear to be moving throughout night and from Stars appear to be moving throughout night and from

night to night…However, it is the earth’s rotation on its night to night…However, it is the earth’s rotation on its axis and revolution that causes the apparent axis and revolution that causes the apparent movement of starsmovement of stars

Constellation: group of stars that are organized Constellation: group of stars that are organized in a recognizable pattern.in a recognizable pattern.

Names come from ancient greeksNames come from ancient greeks

Measuring TimeMeasuring Time

Earth’s motion provides the basis for Earth’s motion provides the basis for measuring timemeasuring time..The day determined by Earth’s rotation on its The day determined by Earth’s rotation on its

axisaxisThe Year is determined by the Earth’s The Year is determined by the Earth’s

revolution around the sun.revolution around the sun.The month is based on the moon’s motion The month is based on the moon’s motion

around Eartharound Earth

Formation of CalendarFormation of Calendar

Many ancient civilization created version Many ancient civilization created version of calendars based on astronomical of calendars based on astronomical cycles.cycles.

Question: If one year is 365 ¼ days long, Question: If one year is 365 ¼ days long, how does our calendar account for this ¼ how does our calendar account for this ¼ day?day?LEAP YEAR-every four years, February has LEAP YEAR-every four years, February has

29 days as opposed to 28 days.29 days as opposed to 28 days.

Time ZonesTime Zones

Use the sun as the basis for measuring time.Use the sun as the basis for measuring time. Noon: when the sun is highest in the skyNoon: when the sun is highest in the sky Because of Earth’s rotation, sun is highest at Because of Earth’s rotation, sun is highest at

different time throughout the Earth different time throughout the Earth Earth Earth divided into 24 time zones.divided into 24 time zones. Noon is set as the time when the sun is highest over Noon is set as the time when the sun is highest over

the center of that zone.the center of that zone.

International Date Line: line that runs from north to International Date Line: line that runs from north to south through the Pacific Ocean. When it is Friday south through the Pacific Ocean. When it is Friday west of the line, it is Thursday East of the line.west of the line, it is Thursday East of the line.

The SeasonsThe Seasons

Earth’s axis is tilted at 23.5 degreesEarth’s axis is tilted at 23.5 degrees

SeasonsSeasons

Changes in the angles at which the sun’s Changes in the angles at which the sun’s rays strike Earth’s surface cause the rays strike Earth’s surface cause the seasons.seasons.

North Pole away from sun North Pole away from sun angle of angle of sun’s rays falling on the N. Hemisphere is sun’s rays falling on the N. Hemisphere is low low sun’s rays spread solar energy sun’s rays spread solar energy over a large area, which leads to lower over a large area, which leads to lower temperatures temperatures few daylight hours few daylight hours WINTERWINTER

EquinoxesEquinoxes

The seasons fall and spring begin on days The seasons fall and spring begin on days called called equinoxesequinoxes – the moment when the – the moment when the sun appears to cross the celestial equatorsun appears to cross the celestial equator..

Celestial equatorCelestial equator: a line drawn on the sky : a line drawn on the sky directly overhead from the equator of the directly overhead from the equator of the earth.earth.

SolsticesSolstices

The seasons of summer and winter begin The seasons of summer and winter begin on days calledon days called solisticessolistices – point at which – point at which the sun is as far north or as far south of the sun is as far north or as far south of the equator as possiblethe equator as possible

Summer: Most hours of daylight in the N. Summer: Most hours of daylight in the N. HemisphereHemisphereThe farther north of the equator you are, the The farther north of the equator you are, the

longer the period of daylight.longer the period of daylight.E.g. North of the Arctic Circle, there are 24 hours E.g. North of the Arctic Circle, there are 24 hours

of daylight at summer solsticeof daylight at summer solstice