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• The Earth is not the center of the universe; it's one of eight planets orbiting the sun.
• The sun is one of billions of stars in the Milky Way galaxy.
• The Milky Way is one of billions of galaxies in the universe.

Gravitational Forces

• Objects in the solar system orbit the sun due to the sun's immense gravitational pull.
• The sun contains over 99% of the solar system's mass.
• The sun's diameter is 100 times that of Earth and 10 times that of Jupiter.

Earth's Motion

• Earth moves through space like riding in an airplane.
• The earth seems still but it moves through space.

Earth's Orbit

• Earth moves around the sun due to the gravitational pull of the sun.
• Without this force, Earth would move in a straight line.
• Earth's orbit is elliptical, almost circular.
• The orbit of one body around another is called an orbit.
• Earth takes 365.25 days, or one year, to orbit the sun.
• The distance between Earth and the sun varies.
• One astronomical unit (AU) represents the average distance between Earth and the sun, approximately 150 million kilometers.
• Astronomers often use astronomical units to measure distances within the solar system.

Earth's Axial Rotation

• Earth spins on its axis, an imaginary line from the North Pole to the South Pole.
• Axial rotation causes day and night as different parts of Earth face the sun.
• The Earth completes one rotation in approximately 24 hours.

Earth's Tilt and Seasons

• Seasons are caused by the tilt of Earth's axis, not by Earth's distance from the sun.
• Earth is closest to the sun in January, during winter in the Northern Hemisphere.
• The constant tilt changes the amount of direct sunlight received by each hemisphere.

Equinoxes

• During equinoxes in March and September, Earth's axis is neither toward nor away from the sun.
• "Equinox" means "equal night"; day and night hours are equal.
• Equinoxes mark the start of spring and autumn.

Solstices

• Solstices occur in June and December when Earth's axis is tilted most toward or away from the sun.
• The summer solstice in the Northern Hemisphere occurs when the North Pole is oriented towards sun.
• The hemisphere receives more direct sunlight and longer daylight hours during the summer solstice.
• The winter solstice in the Northern Hemisphere occurs when the North Pole is oriented away from the sun.
• The hemisphere receives less direct sunlight and shorter daylight hours during the winter solstice.
• Seasons are reversed after six months.

Earth's Moon

• Gravity keeps the moon in orbit around Earth.
• The moon is about one-quarter Earth's size and lacks an atmosphere
• The moon's surface is rocky and covered in mountains, plains, and impact craters.

Moon Formation

• Scientists believe the Moon formed from debris after a massive object collided with Earth.
• Gravity caused space debris to accumulate and form the Moon.

Moon's Movements

• The Moon rotates on its axis and orbits Earth.
• The moons rotation around its axis takes 27.3
• The same side of the Moon always faces Earth because the Moon's rotation matches its orbital period.
• The side of the Moon not visible from Earth is called the far side.

Moon Phases

• The moon does not create its own light, and can only be seen because it reflects the Sun's light
• As the Moon orbits Earth, the visible portion changes, creating lunar phases.
• The moon completes a cycle of phases every 29.5 days.

Waxing and Waning Phases

• During the new moon phase, the Moon is between Earth and the sun, so the sunlit side faces away from Earth, located in its shadow.

• Over the next two weeks after the new moon, as more of the Moon becomes visible, this is called the waxing phase.

• The phases during the waxing phrase are: waxing crescent, first quarter, and waxing gibbous.

• The part of the Moon illuminated by sunlight faces the Earth when the Earth is between the Moon and Sun.

• This period will be one day, and is known as a full moon

• Part of the Moon that is facing the Sun begins to shrink over the next two weeks

• This is known as waning.

• The phases of the waning phrase are: waning gibbous, last quarter and waning crescent.

Tides

• Tides are the periodic rise and fall of ocean levels.
• Tides are caused by the gravitational pull between Earth, the Moon, and the sun.
• The Moon's influence on tides is about twice that of the sun due to its closer proximity to Earth.

Influence of the Moon

• Locations on Earth closest to and farthest from the Moon experience the greatest tidal effects.
• Higher water levels occur at high tide, and the areas move along as the Earth orbits its axis.
• Areas between regions of high tides will experience lower tides during rotation.
• Changes occur with tides can be predicted in a variety of ways.
• Most coastlines experience two high and low tides daily, with tides being affected by weather, depth and the shape of the coastline.

Influence of the Sun

• Tidal ranges become more extreme when Earth, the Moon, and the sun are aligned.
• Tidal stretches in strength are known as spring tide.
• When the Moon is in its first and third quarters, the gravitational pull results in the strength being vertical with attraction of the Sun.
• In this case tide variations are lower than normal, known as neap tides.

Eclipses

• Eclipses occur when one object in the solar system passes into the shadow of another.
• Solar and lunar eclipses can be observed from Earth.

Solar Eclipse

• A solar eclipse can only occur during the new moon phase.
• During a solar eclipse, a small portion of Earth is in the Moon's shadow, where the sun appears partially or fully blocked.

Lunar Eclipse

• A lunar eclipse can only occur during the full moon phase.

During a lunar eclipse, Earth's shadow blocks the Moon partially or completely.

• The Moon turns red during a total lunar eclipse as light bends through Earth's atmosphere.