1. Earth in Space
6.E.1.1 Explain how the relative motion and relative position of the sun, Earth and moon affect the seasons, tides, phases of the moon, and eclipses.

2. History
Each year, ancient Egyptian farmers eagerly awaited the flood of the Nile River. For thousands of years, their planting was ruled by it. As soon as the Nile’s floodwaters withdrew, the farmers had to be ready to plow and plant their fields along the river. Therefore, the Egyptians wanted to predict when the flood would occur.

3. History (Cont.)
Around 3000 b.c., people noticed that the bright star Sirius first became visible in the early morning sky every year shortly before the flood began. The Egyptians used this knowledge to predict each year’s flood. The ancient Egyptians were among the first people to study the stars. The study of the moon, stars, and other objects in space is called astronomy.

4. How Earth Moves
Earth moves through space in two major ways: rotation and revolution.
Rotation - A turning or moving about a central point.
Revolution - following a path in space around another object.

5. Rotation
The imaginary line that passes through Earth’s center and the North and South poles is Earth’s axis. The spinning of Earth on its axis is called rotation.
Earth’s rotation causes day and night. As Earth rotates eastward, the sun appears to move westward across the sky. It takes Earth about 24 hours to rotate once. As you know, each 24-hour cycle of day and night is called a day.

6. Revolution
In addition to rotating on its axis, Earth travels around the sun. Revolution is the movement of one object around another. One complete revolution of Earth around the sun is called a year. Earth follows a path, or orbit, as it revolves around the sun. Earth’s orbit is not quite circular. It is a slightly elongated circle, or ellipse.

7. Calendars
People of many different cultures have struggled to establish calendars based on the length of time that Earth takes to revolve around the sun. A calendar is a system of organizing time that defines the beginning, length, and divisions of a year.

8. Calendars (Cont.)
The ancient Egyptians created one of the first calendars. Egyptian astronomers counted the number of days between each first appearance of the star Sirius in the morning. In this way, they found that there are about 365 days in a year.
The time from one full moon to the next is about 29 ½ days.

9. Calendars (Cont.)
The Romans borrowed the Egyptian calendar of 365 days. But in fact, Earth orbits the sun in about 365 ¼ days. The Romans adjusted the Egyptian calendar by adding one day every four years. You know this fourth year as “leap year.” During a leap year, February is given 29 days instead of its usual 28. Using a system of leap years helps to ensure that annual events, such as the beginning of summer, occur on the same date each year.

10. 1. Spring 2. Summer 3. Fall (or Autumn) 4. Winter
The Seasons on Earth
1. Spring 2. Summer 3. Fall (or Autumn) 4. Winter

11. The Seasons
The cause of the seasons can be attributed to the tilt of the earth’s axis. The axis around which the earth rotates every day is tipped 23.5 degrees.
In summer, we are tipped toward the sun. When we are tipped toward the sun, the sun’s rays beat down upon the earth from almost straight overhead. In winter, we are tipped away from the sun. When we are tipped away from the sun, the sun’s rays beat down upon the earth from a sharp angle.

13. Notice that sunlight hits Earth’s surface most directly near the equator. Near the poles, sunlight arrives at a steep angle. As a result, it is spread out over a greater area. That is why it is warmer near the equator than near the poles.

14. Angles
The two extremes of angles are on June 21st where the sun is at its highest noon and on December 21st where the sun is at its lowest noon.
The tilt of the earth’s axis causes the number of daylight hours to vary during the year. In summer the sun rises around 5:00 A.M. or so but doesn’t set until after 9:00 P.M. The daylight hours in winter are very short comparatively.

16. Notice as Earth’s axis is always tilted at an angle of 23
Notice as Earth’s axis is always tilted at an angle of 23.5° from the vertical. As Earth revolves around the sun, the north end of its axis is tilted away from the sun for part of the year and toward the sun for part of the year.

17. Summer and winter are caused by Earth’s tilt as it revolves around the sun. The change in seasons is not caused by changes in Earth’s distance from the sun. In fact, Earth is farthest from the sun when it is summer in the Northern Hemisphere.

19. Terms
Solstice – The two days of the year on which the sun reaches its greatest distance north or south of the equator.
Aphelion - The time of the year when the Earth is farthest from the sun.
Perihelion - The time of the year when the Earth’s orbital path brings it closest to the sun.
Equinox – The two days of the year on which neither hemisphere is tilted toward or away from the sun; also, day and night are of equal duration.

20. Equinoxes
The two yearly equinoxes occur when the Sun crosses the celestial equator. 1. Vernal (spring) equinox - occurs on March Autumnal equinox - occurs on September or 22.

21. QUESTIONS
Which is one reason why Earth experiences seasons? A. distance from the sun B. distance from the moon C. tilt of the Earth D. tilt of the moon

22. The diagram below shows Earth and the Sun during June
The diagram below shows Earth and the Sun during June. During June, which location on Earth receives the most direct sunlight? A. 1 B. 2 C. 3 D. 4

23. What season is the Earth tipped away from the sun. A. Summer B
What season is the Earth tipped away from the sun? A. Summer B. Winter C. Autumn (Fall) D. Spring

24. What are the two dates in which the angles of the sun are the most extreme?
A. July 4 and December 25
B. February 14 and October 31
C. March 21 and September 21
D. June 21 and December 21

25. THE END