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).

Force of gravity depends on… 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

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.

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.

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

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.

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!

Lunar Eclipse Full Moon phase, Sun, Earth, Moon

Solar Eclipse Moon Phase: New Moon, Sun, Moon, Earth

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, Watch for it!

Earth Moon Tides Tides are 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. The influence of the Moon’s gravitational force acting on the Earth’s oceans and the Earth (the rocky part). What causes tides?

Earth Moon Sun High Tide High Tide Low Tide Low Tide 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).

Earth Moon Moon 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. New Moon Phase of the moon? Full Moon Phase of the moon? Moon New Moon Phase of the moon? Higher high tides and lower low tides

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

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!) Moon also brakes the Earth's Rotation Moon's orbit is growing because of all of this interaction. We see a permanent "near" and "far side" of the Moon. The length of the "day" is increasing!  From fossil reef corals of about 4  10 8 years old - daily growth/annual growth  400 days/year ~ 22 hours a day!  Day is increasing about seconds/century. Therefore, the day is getting longer, Moon looks smaller, and tides are weakening.

Season’s The tilt of the earth causes the Season’s

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.

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).

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.

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.

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.