Chapter 20

1. Chapter 20 Earth Sun Moon

2. Lesson 1 • Earth rotates on a tilted imaginary axis and orbits the sun • Earth’s rotation causes day and night • Earth’s gravity pulls objects toward the center-south is down everywhere • About half the Earth is in sunlight while the other half is dark

3. Earth’ tilt and orbit cause seasons • Earth’s rotation defines day and night • Earth’s orbit defines seasons • Earth makes one revolution around the sun a year (365 days-12 months) • Earth’s orbit is not a perfect circle

4. Seasonal Patterns • Hemisphere is half of the globe (northern and southern) • Patterns of temperature and weather trends change throughout a year and are called seasons (summer, winter, fall, spring)

5. Equinox vx Solstice • September Equinox-Sun shines equally on 2 hemispheres-Fall/Spring • December Solstice-North leans away from sun-Winter/Summer (shortest day) • March Equinox-Sun shines equally on 2 hemispheres-Spring/Fall • June Solstice-North leans toward sun-Summer/Winter (longest day)

6. Length of Days • The farther you get away from the equator, the more extreme changes in day and night • The closer you get to the equator, the more equal amounts of time in day and night • On equator=12 day 12 night hours • On poles=20+ day/6 months changes

7. Angles of Sunlight • When the sun is high in the sky (directly above you), the sunlight is concentrated in one area-right angle-shadows are short- between 10 and 2 • When the sun is low in the sky, the sunlight strikes the ground at an obtuse or acute angle-not concentrated-shadows are long-early morning or late afternoon

8. Lesson 2 • The moon is Earth’s natural satellite • The moon rotates once per orbit of Earth • Gravity keeps the moon in orbit • The moon is Earth’s closest neighbor • It takes astronauts 3 days of travel to reach the moon

9. Moon’s craters show history • Mare-dark area on the moon • Lunar means moon • All the features that can be seen on the moon are different types of solid or broken rock • Moon has no air, no oceans, no clouds, no life

10. Craters • Light colors designate high altitude-highlands • Have many round features called craters that formed when small objects from space hit the surface • Moon’s lighted side has many large dark colored spots • Moon’s dark side has mostly highlands

11. Moon Rocks • Different ages (some 4.5 billion years) • The older rocks are found in the highlands • The new rocks are found in the dark maria areas • Rock covers the entire moon surface • Basalt is a common rock on the moon

12. Layers of the Moon • Remains mostly unchanged for billions of years • Structure: Crust, mantle and core • Similar materials in Earth and the moon but in different proportions • Evidence from rocks show that the moon was once closer to Earth (3.8 cm yearly)

13. Lesson 3 • Positions of the Sun and Moon affect Earth • Eclipse • Tides • Waxing vs Waning • Phases-orbits the Earth monthly

14. Waxing and Waning • Waxing is1-2 week of the month • Waning is 3-4 week of the month • New moon-when the Earth, moon and sun are all lit in the same direction • Full moon-half way through cycle/month when the whole near side of the moon is in sunlight-the moon and sun are in opposite directions (p. 701)

15. Waxing means growing and waning means shrinking • The appearance of the moon depends on the positions of the sun, moon, and Earth

16. Crescent and Gibbous • Crescent moons occur when the moon appears close to the sun in the sky-visible during daytime or around sunrise or sunset • Gibbous and full moons appear far from the sun in the sky-more noticeable at night

17. Lunar eclipse • Moon becomes dark during a lunar eclipse because it passes through Earth’s shadow • Just before a lunar eclipse, sunlight streaming past Earth produces a full moon • A total lunar eclipse occurs when the moon passes completely into shadow

18. Solar Eclipse • Solar eclipse occurs when the moon passes directly between the Earth and sun • The sun seems to darken because the moon’s shadow falls onto part of Earth • Moon covers the sun and the sky becomes as dark as night • Do not ever look at a solar eclipse

19. Ocean Tides • Average ocean water level rises slowly for about 6 hours to high tide • Then it lowers for about 6 hours to low tide • Entire pattern takes about 24 hours • 2 high and 2 low tides per day

20. Tides • Tides occur because the moon’s gravity changes the shape of Earth’s oceans • Moon pulls on different parts of Earth with different amounts of force • Earth’s crust is hard enough to resist being pulled into a different shape, but Earth’s oceans do change shape

21. Tides • Moon’s pull produces a bulge of thicker ocean water on the side of Earth nearest to the moon (picture on page 706) • Another bulge of water is produced on the side of Earth farthest from the moon because the moon pulls the center of Earth away from that side • Thin layers of water run in between bulge

22. Chapter Review page 709 • Earth rotates on a tilted axis and orbits the sun (day/night and seasons) • Moon is Earth’s natural satellite with many similar characteristics as Earth • Positions of the sun and moon affect Earth

23. Time to test ….. • Study vocabulary and pictures noted throughout the chapter • Keep notes neat and organized in binder • Complete and study chapter review on page 709