EARTH'S MOTION

Rotation The spin of the Earth on its axis (rate of 15 /hr) Earth is tilted at an angle of 23.5 degrees from perpendicular The Earth’s axis is always tilted in the same direction throughout its orbit (parallelism)

Evidence of Movement Foucault Pendulum- Changes its direction of swing over time Coriolis Effect- The deflection of air and water to the right in the northern hemisphere Sorry, Bart Simpson was not right. Water DOES turn counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere, HOWEVER… in toilets, the direction is caused by the force of the pump, not CORIOLIS!

Solar Time The measurement of time based on the apparent movement of the sun through the sky Solar Noon is the time of day when the sun is at its highest altitude above the horizon Problem - solar noon does not occur at the same time for everyone (solar noon differs by approx. 1 minute for every 12 miles east/west of a specific location)

To make up for this “problem”, time zones were established (each 15 longitude wide – 1 hour of rotation) Time zones begin at the Prime Meridian Every 15 degrees EAST is +1 hour, every 15 degrees WEST is –1 hour Clock time is the average solar time

Revolution movement of the Earth around the sun in its elliptical orbit One complete revolution is 365.25 days (1 year) In conjunction with AXIAL TILT, this causes a change in the seasons no tilt of the axis = no seasonal changes Evidence of movement: Change in visible constellations throughout the year

Solstices and Equinoxes SOLSTICE - extremes from the sun WINTER (perihelion) – 8 hours day/16 hr night SUMMER (aphelion) – 16 hours day/8 hr night EQUINOX – equal distances from the sun (equal days/nights) Autumn (Vernal), Spring – 12 hours day/night

Nighttime on the Artic Circle during the Summer. The sun never sets Nighttime on the Artic Circle during the Summer. The sun never sets! It’s always on the horizon.

Causes of Seasons Earth’s revolution Tilt of the Earth on its axis Parallelism More sunshine = more energy = warmer time of year Less sunshine = less energy = cooler time of year