Chapter 11 The Earth, Sun and Moon

1. Chapter 11 The Earth, Sun and Moon

2. Planet Earth • Earth’s Shape • Sphere, a round 3-D object whose points are all the same distance from the center. • Not a perfect sphere because it bulges at the equator and flattens at the poles due to its rotation.

3. Aristotle • Greek astronomer who first reasoned that the earth was a sphere • How did he know? • The earth always casts a round shadow on the moon during a lunar eclipse. • The tops of ships sailing across the ocean would always come into view first

4. Earth Facts • Day Length = 23 hrs. 56 min. = 1 rotation, gives us night and day • Year Length = 365 days, 6 hrs. 9 min. = 1 revolution • All units of time are based on a comparison of the Earth’s position to that of the sun. • Distance = 93,000,000 miles (avg.) 1 Astronomical Unit (A.U.) • Circumference at Equator = 24,900 miles.

6. Seasons • The Earth’s Revolution • Describes the path of the Earth’s orbit, which is an ellipse that causes the Earth to be at different distances from the sun. • Jan. 3 closest to the sun • July 4 furthest from the sun • Has very little effect on the seasons.

7. The Earth’s Tilted Axis • The axis is tilted 23.50 • This tilt plus the Earth’s shape is the reason for the seasons, because it causes each hemisphere to receive different amounts of direct and indirect sunlight. • Tilt and shape also affects the number of daylight and nighttime hours. The hemisphere tilted towards the sun receives more hours of daylight.

8. N. Hemisphere is Toward the Sun • Summer in the north and winter in the south • Longer days in the north and shorter in the south • Sun is higher in the sky in north and lower in the south • More direct sunlight in the north and less in the south • Sun is directly over the Tropic of Cancer

10. Equinox • The two times a year the sun is directly over the equator. • The number of daylight hours is equal to the number of nighttime hours. • Neither hemisphere is tilted toward the sun.

11. Solstice • The two times a year that the sun is at its greatest distance north or south of the equator. • Represents the longest and shortest days of the year

12. Earth-SunRelations

14. The Moon • Rotation & Revolution • The moon rotates on it’s axis once every 27.3 days • The moon revolves around the earth once every 27.3 days • Conclusion: The same side of the moon is always facing the earth. • The plane of the moons orbit is not the same as the earths, which allows the moon to be seen at different positions in the sky as well as be seen during the day.

15. Why does the moon shine? The side facing away from Earth The side we see from Earth • Because it reflects sunlight from it’s surface.

16. Phases of the Moon • The changing appearances of the moon as seen from earth. (why?, because the moon orbits earth) • 2 Types of Phases • Waxing • The process of more and more of the moon’s lighted side becoming visible from the earth. (moon getting bigger) • Waning • The process of less and less of the moon’s lighted becoming less visible from earth. (moon getting smaller)

17. Waxing Phases New Moon Waxing Crescent First Quarter Waxing Gibbous

18. Waning Phases Full Moon Waning Gibbous Third Quarter Waning Crescent

20. Phase Definitions • New Moon • Occurs when the moon is between the earth and the sun. • The lighted side is facing away from the Earth. • Crescent Moon • ¼ of the lighted side of moon is visible. • occurs 24 hours after new moon

21. Phase Definitions • Quarter Moon • ½ of the lighted side is visible from Earth • Occurs 1 week after the previous phase. • Gibbous Moon • ¾ of the lighted side is visible from Earth. • Occurs 1 week after the previous phase. • Full Moon • Occurs when all the lighted side is visible from Earth, the Earth is between the sun and moon

23. Moon Phase Quiz Phase order Phase Position

24. Eclipses • What causes an eclipse? • The revolution of the moon around the Earth. • When do they occur? • When the Earth or moon temporarily blocks the sunlight from reaching the other. • When the sun, Earth and moon are perfectly aligned.

25. Solar Eclipse • The moon is directly between the earth & sun • Moon moves from right to left across the sky and blocks right (east) side of sun first • Very difficult to see due to the small shadow created by the moon. • Can only be seen by the people directly under the Umbra.

26. Solar Eclipse • Can only occur during the new moon phase. • Umbra • Darkest portion of the moon shadow • The only place a total solar eclipse can be seen. • Penumbra • The lighter shadow that surrounds the umbra • Only a partial eclipse can be seen below this shadow

33. Lunar Eclipse • Last longer, because the earth is bigger & casts a bigger shadow • Occurs when the earth’s shadows fall on the moon • Only those on the nighttime side of the earth can see it • The west side of the moon is covered first • Occurs during the full moon phase

38. Origin of the Moon • The moon formed elsewhere and then was captured by the earth’s gravity. • The moon condensed from loose material during the early formation of the solar system • Impact theory: A blob of molten material was ejected/thrown from the earth when a mars-sized object collided with the earth. The gas and debris then condensed to form the moon over 4.6 billion years ago. • A blob of molten material was thrown from the earth during its molten stage that formed the moon.