1. 26.2 Movements of Earth

2. The Rotating Earth
The Spinning of Earth on its axis is called ROTATION.
How long does each rotation take?
One Day
Earth rotates from West to East, sun appears to rise in the east in the morning, cross the sky, and set in the west.

3. Foucault Pendulum 19th centruy, Jean-Bernard-Leon Foucault
Provided evidence of Earth’s rotation
Observed that the path of the pendulum appeared to change over time…
BUT, it was the floor that was moving while the pendulum’s path stayed constant.
Because the floor was attached to the Earth, he concluded that the Earth rotates

4. Foucault
Pendulum in
Paris

6. The Coriolis Effect Evidence of the Earth’s rotation
Observations in ocean surface currents and wind belts.
Earth’s rotation causes ocean currents and wind belts to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere
This curving/deflection of wind and ocean currents caused by Earth’s rotation is called the Coriolis effect.

8. Revolving Earth
Earth travels around the sun at an average speed of 29.8 km/s
The motion of a body that travels around another body in space is called a Revolution
How long is one complete revolution of Earth?
365 ¼ days

9. Earth’s Orbit
Orbit: path that a body follows as it travels around another body in space
What do you think the Earth’s orbit around the sun looks like?
Earth’s orbit is an ellipse (“oval”)  Earth is not always the same distance from the sun.
Perihelion: point in orbit when Earth is closest to sun
Aphelion: point in orbit when Earth is furthest from sun

11. Constellations and Earth’s motion
Evidence of Earth’s revolution and rotation can be seen in the motion of constellations.
Stars appear to be moving throughout night and from night to night…However, it is the earth’s rotation on its axis and revolution that causes the apparent movement of stars
Constellation: group of stars that are organized in a recognizable pattern.
Names come from ancient greeks

13. Measuring Time Earth’s motion provides the basis for measuring time.
The day determined by Earth’s rotation on its axis
The Year is determined by the Earth’s revolution around the sun.
The month is based on the moon’s motion around Earth

14. Formation of Calendar
Many ancient civilization created version of calendars based on astronomical cycles.
Question: If one year is 365 ¼ days long, how does our calendar account for this ¼ day?
LEAP YEAR-every four years, February has 29 days as opposed to 28 days.

15. Time Zones Use the sun as the basis for measuring time.
Noon: when the sun is highest in the sky
Because of Earth’s rotation, sun is highest at different time throughout the Earth  Earth divided into 24 time zones.
Noon is set as the time when the sun is highest over the center of that zone.
International Date Line: line that runs from north to south through the Pacific Ocean. When it is Friday west of the line, it is Thursday East of the line.

16. The Seasons
Earth’s axis is tilted at 23.5 degrees

18. Seasons
Changes in the angles at which the sun’s rays strike Earth’s surface cause the seasons.
North Pole away from sun  angle of sun’s rays falling on the N. Hemisphere is low  sun’s rays spread solar energy over a large area, which leads to lower temperatures  few daylight hours  WINTER

19. Equinoxes
The seasons fall and spring begin on days called equinoxes – the moment when the sun appears to cross the celestial equator.
Celestial equator: a line drawn on the sky directly overhead from the equator of the earth.

20. Solstices
The seasons of summer and winter begin on days called solistices – point at which the sun is as far north or as far south of the equator as possible
Summer: Most hours of daylight in the N. Hemisphere
The farther north of the equator you are, the longer the period of daylight.
E.g. North of the Arctic Circle, there are 24 hours of daylight at summer solstice