Earth's Rotation & Revolution

Objectives:

1.    Give evidence for Earth's rotation.

2.    Relate Earth's rotation to the day-night cycle and the time zones.

3.    Give evidence for Earth's revolution around the sun.

4.    Describe Earth's path and rate of revolution.

5.    Explain why the seasons occur.

Key Terms.

rotation        standard time zones        time meridian        prime meridian        International Date Line        revolution        parallax        summer solstice        winter solstice        vernal equinox        autumnal equinox

Notes: (4-2& 4-3)

The success of every species on the planet lies in well they are suited (adapted) to their niche.  Some species are nocturnal while others are diurnal and some species hibernate in the winter while others are active all year long.  The development of of these niches are set up by the rotation and revolution of the Earth.

 Rotation - The spinning of Earth about its axis every 24 hours Revolution - The movement of Earth around the sun every 365.24 days

Rotation:

Although rotation and revolution continue throughout the day and year the axis of rotation and revolution are not on the same plane.

 The axis of rotation is currently 23.5o. Earth's axis points toward Polaris throughout the year exhibiting parallelism

(geography.sierra.cc.ca.us/ .../plane_ecliptic.jpg)

Rotation sets up our day and night cycles.  The rotation was proved by the scientist Foucalt in 1851 when he noticed that his pendulum's sweep direction changed orientation at the rate of 11o per hour.

 The effects of these changes in direction sets up the time zones. Explains the Coriolis effect (apparent deflection of  the wind)

Revolution:

The revolution of the Earth on its axis is important in setting up the seasons.  Evidence for this is in a phenomena called parallax where nearby stars appear to shift with regards to distant stars.

(science.msfc.nasa.gov/.../ batse/IMAGES/PARALLAX.GIF)

The direction of Earth's revolution is in the direction of its rotation.  Because the path around the sun is not circular, we are closer to the sun at certain time of the year.

 Perihelion - point of the orbit closest to the sun (~1-2) Aphelion - point of the orbit furthest to the sun (~7-4)

The tilt of the Earth with its elliptical orbit affect the period of day and night as well as the seasons.  Here are some of the important dates to remember.

Summer solstice

 1st day of summer (6-21) longest day of the year point furthest from the sun maximum tilt towards the sun Latitude is at the Tropic of Cancer North pole receives 24hours of daylight

Winter solstice

 1st day of winter (12-21) shortest day of the year point closest to the sun maximum tilt away from the sun Latitude is at the Tropic of Capricorn North pole receives 24hours of darkness

Vernal & Autumnal Equinox

 The sun hits the equator at 90o Equal day and night throughout the Earth Occurs at 3-21 (Vernal) &  9-22 (Autmnal)

(image: www.usd.edu/esci/figures/ 158280.JPG)

(www.enchantedlearning.com/ egifs/Earthseasons.GIF)