Section 1: Earth in Space

1. Section 1:Earth in Space • How does Earth move in space? • What causes the cycle of seasons on Earth?

2. How Earth Moves • Earth moves through space in two major ways: rotation and revolution. • A revolution is the movement of one object around another. How long does one complete revolution of Earth around the sun take? • Answer: • 365.25 days • (1 year) • Is the Earth’s orbit circular? • No, it is an ellipse.

3. How Earth Moves • The spinning of Earth on its axis is called rotation. As the Earth spins eastward, only half of the planet is facing the sun (day) while the other half is not (night). • How long does it take the • Earth to rotate once? • Answer: 24 hours (1 day)

4. Origin of Calendars • A calendar is a system of organizing time that defines the beginning, length, and divisions of a year. • Over the last 4000 years, they have been based on moon and star cycles, season changes, and sun position. Egyptian calendar What is a leap year? An extra day added every 4 years. Mayan Calendar Stonehenge 1500 B.C.

5. Sunlight Striking Earth’s Surface • Near the equator, sunlight strikes Earth’s surface more directly and is less spread out than near the poles.

6. Seasons on Earth • Earth has seasons because its axis is tilted as it revolvesaround the sun. The axis is always tilted at what angle? 23.5 degrees

7. Common Misconception Alert! • Although the Earth can be at different distances from the sun due to its ellipsoid orbit, this DOES NOT cause the changes in season. In fact, the Earth is farthest from the sun during our summer!

8. Seasons on Earth • The height of the sun above the horizon varies with the season. It is at its lowest angle in winter and highest angle (more direct) in summer.

9. Section 2:Gravity and Motion • What determines the strength of the force of gravity between two objects? • What two factors combine to keep the moon and Earth in orbit?

10. Gravity, Mass, and Distance • The strength of the force of gravity between two objects depends on two factors: the masses of the objects and the distance between them.

11. Four million newtons Reading Graphs: What is the force of gravity on the rocket at the planet’s surface? Gravity Versus Distance

12. One million newtons Reading Graphs: What is the force of gravity on the rocket at a distance of two units (twice the planet’s radius from its center)? Gravity Versus Distance

13. It decreases. Drawing Conclusions: In general, how does the force of gravity pulling on the rocket change as the distance between it and the planet increases? Gravity Versus Distance

14. Gravity and Inertia • Newton concluded that two factors–inertia and gravity–combine to keep Earth in orbit around the sun and the moon in orbit around Earth.

15. Section 3:Phases, Eclipses,and Tides • What causes the phases of the moon? • What are solar and lunar eclipses? • What causes the tides?

16. Motions of the Moon • The changing relative positions of the moon, Earth, and sun cause the phases of the moon, eclipses, and tides. How long does it take the moon to orbit the Earth? 29.5 days

17. Phases of the Moon • The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth.

18. The Moon’s Orbit • The moon’s orbit is tilted about 5 degrees relative to Earth’s orbit around the sun.

19. Solar Eclipse • A solar eclipse occurs when the moon passes directly between Earth and the sun, blocking sunlight from Earth.

20. Lunar Eclipse • During a lunar eclipse, Earth blocks sunlight fromreaching the moon’s surface.

21. Tides • Tides occur mainly because of differences in the force of gravity between the moon and different parts of Earth.

22. Spring and Neap Tides • When Earth, the sun, and the moon are in a straight line, a spring tide occurs (twice a month at new & full moons). • When the moon is at a right angle to the sun, a neap tide occurs (at 1st and 3rd quarter moons).

23. Section 4:Earth’s Moon • What features are found on the moon’s surface? • What are some characteristics of the moon? • How did the moon form?

24. The Moon’s Surface • Features on the moon’s surface include maria, craters, and highlands.

25. The Moon’s Surface • Maria (Latin for “seas”): Dark, flat areas first thought to be oceans, but actually huge ancient lava flows. • Craters: Large round pits caused by the impacts of meteoroids (NOT volcanoes). • Highlands: These are the mountains and crater rims that cover most of the moon’s surface. Why do the maria have fewer craters than the rest of the moon? Most of the impacts occurred before the maria formed.

26. The Moon’s Size • The moon is 3,476 km in diameter, a little less than the distance across the contiguous Untied States. It’s about ¼ the Earth’s diameter.

27. Characteristics of the Moon • The moon is very dry and airless. Since it has no atmosphere, it has large variations in its surface temperature (from 130 degrees Celsius in direct sunlight to -180 degrees at night). • The moon is made out of much of the same elements that make up the Earth such as oxygen, silicon, magnesium, potassium, nickel, sulfur among many others. • Though it’s ¼ the diameter of Earth, it only has 1/80th of the mass. This causes its gravity to be about 1/6 of what it is here on Earth. • What would you weigh on Earth? Divide your weight by six.

28. The Origin of the Moon • Scientists theorize that a planet-sized object collided with earth to form the moon.

29. The Origin of The Moon • Moon Mysteries Part One