1. Table of Contents Title: Natural Time Periods Page #: 15
Date: 9/20/2012

2. Objective
Students will be able to find the Equator, the Tropic of cancer and the tropic of Capricorn on a map.
Students will be able to describe how Earth’s position relative to the Sun determines the length of sunlight that Earth receives in a day during different seasons.
Students will be able to compare and contrast Geologic Time with Natural Time.

3. Words of the Day
Rotation - A complete turn of the earth on its axis from west to east.
Revolution - A complete trip of the earth around the Sun.

4. Natural Time Periods
Time - Used to describe the starting point of an event, the event’s duration and the rate at which the event proceeds.
Natural Periods - Time periods based on Earth’s orbit around the Sun.
1 Year = 365 and 1/4 days - The time it takes Earth to make one revolution around the Sun.

5. Natural Time Periods
1 Day = 24 Hours - The time it takes for Earth make one full rotation on its axis.
Axis - The point around which Earth rotates.
Earth’s axis is 23.5º away from vertical.
Rotation West to East
23.5º
Equator 
Axis 

6. Natural Time Periods
Summer Solstice (June 22)- The day of the year during which the Northern Hemisphere receives the longest period of daylight.
The sun is aligned with the Tropic of Cancer = 23.5º North of the Equator.
Winter Solstice (December 21) - The day of the year during which the Northern Hemisphere receives the shortest period of sunlight.
The sun is aligned with the Tropic of Capricorn = 23.5º South of the Equator.
Tropic of Cancer
Tropic of Capricorn

7. Natural Time Periods Arctic Circle 66.5° North of the Equator.
Antarctic Circle
66.5° South of the Equator
Artic Circle
Antarctic Circle

8. Natural Time Periods Vernal Equinox (March 21)
Start of Spring in the Northern Hemisphere.
The sun is directly in line with the equator.
Length of sunlight and darkness are equal all over the world.
Autumnal Equinox (September 23)
Start of Autumn in Northern Hemisphere.
The sun is directly in line with equator.
Sun
Earth
Earth
Sun

10. Classwork Compare and contrast Geologic Time to Natural Time.
1. Describe some intervals that Geologic Time is divided into. How are those intervals determined?
2. Describe some intervals that Natural Time is divided into. How are those intervals determined?
3. What time scale, Geologic or Natural, is more useful when making plans with your friends?