What is Gravity?

2. What is Gravity? Gravity is an attraction that acts between any two objects that have a mass. However, this is only significant if one or both of the objects are very massive (like a planet, star, or moon).

3. Mass - The more massive an object, the greater the gravity Distance - The closer an object is, the greater the gravity. *This is why we are stuck on Earth and not pulled away to the sun even though the sun is much more massive than the earth Force of gravity depends on…

4. Newton's Law of Universal Gravitation • The force of attraction between two objects is directly related to the masses of the objects and inversely related to the square of the distance between them.

5. Orbital Speed • The speed at which an object orbits around another object. Example: The Earth’s orbital speed is 67,000 mph. It travels 67,000 mph around the sun.

6. Inertia and Gravity • Inertia is too great • Gravity too great * To stay in orbit, inertia and gravity must be balanced

8. Moon Terms • Waxing – The moon appears more lit each night. • Waning – The moon appears less lit each night. • Crescent – Less than half of the moon appears lit. • Gibbous – More than half of the moon appears lit. • First Quarter – The right half of the moon appears lit. • Third Quarter – The left half of the moon appears lit. • Full Moon – The entire moon appears lit. • New Moon – No part of the moon appears lit.

9. REMEMBER! One half of the moon is lit at all times by the sun, except during a lunar eclipse. We name the phase according to what WE see!

10. Lunar Eclipse • Full Moon phase, Sun, Earth, Moon

11. Solar Eclipse • Moon Phase: New Moon, Sun, Moon, Earth

12. Why no eclipse every month? The moon’s orbit is at a 5 degree angle, so Earth only occasionally gets in the way. The next total lunar eclipse in this area will be April 14, 2014. Watch for it!

13. Tidesare the vertical movement of water, specifically the alternate rise (flood or flow) and fall (ebb) of water in the ocean. This is mostly noticeable along continental shorelines. Moon Earth What causes tides? The influence of the Moon’s gravitational force acting on the Earth’s oceans and the Earth (the rocky part).

14. Tides are more influenced by the gravitational effect of the Moon than they are by that of the Sun (the Moon's closeness to us outweighs by far the Sun's greater size). Low Tide Moon Earth High Tide High Tide Low Tide Sun

15. Spring Tides • The gravitational affects of the moon and sun combine to influence the flow of the oceans on Earth. • Spring tides are formed when the Sun, Earth, and Moon are in a line. Moon Moon Moon Earth Phase of the moon? Phase of the moon? Phase of the moon? New Moon Full Moon New Moon • Higher high tides and lower low tides

16. Neap Tides The gravitational affects of the moon and sun fight each other with their influence on the flow of the oceans on Earth. Phase of the moon? Moon Phase of the moon? Moon Third Quarter Third Quarter Neap Tides form an L with the sun, moon and earth. Earth Phase of the moon? Moon First Quarter Lowest high tides and highest low tides

19. Tides & Consequences • This little tidal behavior goes both ways! The Earth rises tides on the Moon. • The Earth "brakes" the Moon's rotation AND the braking is complete! Synchronous Rotation of the Moon and its orbital period! (27.3 days!) • We see a permanent "near" and "far side" of the Moon. • Moon also brakes the Earth's Rotation • The length of the "day" is increasing! • From fossil reef corals of about 4´108 years old - daily growth/annual growth  400 days/year ~ 22 hours a day! • Day is increasing about 0.001 seconds/century. • Moon's orbit is growing because of all of this interaction. Therefore, the day is getting longer, Moon looks smaller, and tides are weakening.

20. Season’s Fall • The tilt of the earth causes the Season’s Winter Summer Spring

21. How Do Days Change in Length? • Summer, days are longer and nights are shorter. • Winter, days are shorter and nights are longer. • The reason days change in length is the same reason we have seasons: Earth’s axial tilt.

22. Earth’s Axis Is on a Tilt. • Earth is tilted at a 23 ½ degree angle from the vertical. • The axis is always tilted in the same direction; the north pole is always pointed towards the North Star (Polaris).

23. Around June 21, the North Pole of the axis is tilted toward the sun. This is the longest day of the year for the Northern Hemisphere and the shortest for the Southern Hemisphere. • Around December 22, the North Pole of the axis is tilted away from the sun. This is the shortest day of the year for the Northern Hemisphere and the longest day of the year for the Southern Hemisphere. • Around March 20 and September 23, the sun is directly over the equator. Days and nights are equal length everywhere on Earth.

24. Earth’s Uneven Heating • Earth’s temperature varies with latitude. • At higher latitudes, solar radiation is less intense. • The same thing happens to the sun’s energy when it reaches the south pole at an angle.

26. Why is it not the distance? • The distance of the Sun and Earth is not that different at different positions, so light intensity is affected very little.