1. Unit 3 The Earth-Moon-Sun System
The Big Idea:
Earth & the moon move in predictable ways & have predictable effects on each other as they orbit the sun.

2. Unit 3 Lesson 1 Earth’s Days, Years, and Seasons
Spinning in Circles
Rotation- the spinning of a body, such as a planet, on its axis (called a day)
Earth rotates counterclockwise
Earth rotates west to east
Only ½ of Earth faces the sun
Each planet spins on its axis.
The time it takes a planet to complete one full rotation on its axis is called a day.
Earth rotates in a counterclockwise motion around its axis when viewed from above the North Pole.
As a location on Earth’s equator rotates from west to east, the sun appears to rise in the east, cross the sky, and set in the west.
Only one-half of Earth faces the sun at any given time.
People on the half of Earth facing the sun experience daylight, and this period is called daytime.
People on the half of Earth facing away from the sun experience darkness, and this period is called nighttime.
Earth completes one rotation on its axis in 24 hours, or one day.

3. Unit 3 Lesson 1 Earth’s Days, Years, and Seasons
Revolution- the motion of a body that travels around another body in space
Earth revolves the sun in 365 ¼ days
As Earth rotates on its axis, it also revolves around the sun.
The motion of a body that travels around another body in space is called revolution.
Earth completes a full revolution around the sun in 365 ¼ days, or about one year. We have divided the year into 12 months, each lasting 28 to 31 days.

4. Tilt-a-Whirl Earth is titled at 23.5˚
Unit 3 Lesson 1 Earth’s Days, Years, and Seasons
Tilt-a-Whirl
Earth is titled at 23.5˚
During each revolution, the North Pole may be tilted toward the sun or away from the sun.
When the North Pole is tilted toward the sun, the Northern Hemisphere has longer periods of daylight than the Southern Hemisphere has.
When the North Pole is tilted away from the sun, the opposite is true.
The angle at which the sun’s rays strike each part of Earth’s surface changes as Earth moves in its orbit.
When the North Pole is tilted toward the sun, the sun’s rays strike the Northern Hemisphere more directly, and this region is warmer.
When the North Pole is tilted away from the sun, the sun’s rays strike the Northern Hemisphere less directly, and this region is cooler.
The spherical shape of Earth also affects how the sun warms up an area.
At a point near the equator, the sun’s rays hit Earth’s surface more directly, so temperatures are higher there.
At a point near one of the poles, the sun’s rays hit Earth’s surface less directly, so temperatures are lower there.
The number of daylight hours on any given day of the year varies with location.
Areas around Earth’s equator receive about 12 hours of light a day.
Areas on Earth’s surface that are tilted toward the sun have longer than 12-hour days, as they travel a longer path through the lit part of Earth.
Areas on Earth’s surface that are tilted away from the sun have shorter than 12-hour days, as they travel a shorter path through the lit part of Earth.
During summer in the Northern Hemisphere, areas north of the Arctic Circle receive 24 hours of daylight.
At the same time, areas south of the Antarctic Circle receive 24 hours of darkness.
In winter in the Northern Hemisphere, the polar areas experience the reverse conditions.

5. Unit 3 Lesson 1 Earth’s Days, Years, and Seasons
Seasons change…
Seasons – a specific time of the year that is characterized by recurring weather conditions
Equinox- sun shines equally on both hemispheres
Solstice- area of sunlight is maximum in one hemisphere & minimum in the other
Most locations on Earth experience seasons. Each season is characterized by a pattern of temperature and other weather trends.
We experience seasons due to changes in the intensity of sunlight and the number of daylight hours as Earth revolves around the sun.
Half of each hemisphere is lit, and half is in darkness.
As Earth moves along its orbit, the sunlight reaches more of one hemisphere than the other.
During the September equinox, sunlight shines equally on both poles.
During the March equinox, half of each hemisphere is lit, and the sunlight is centered on the equator.
At the December solstice, the North Pole leans away from the sun and is in complete darkness, and the South Pole is in complete sunlight.
At the June solstice, the North Pole leans toward the sun and is in complete sunlight, and the South Pole is in complete darkness.

6. Unit 3 Lesson 1 Earth’s Days, Years, and Seasons

7. Unit 3 Lesson 2 Moon Phases and Eclipses
Round and Round They Go!
Moon – natural satellite that travels around planets (revolution 28.5 days)
Gravity – force that pulls all bodies that have mass toward other objects.
Earth spins on its axis and orbits around the sun.
A body that orbits a larger body is called a satellite.
Earth’s gravitational pull on the moon keeps the moon in orbit, forming the Earth-moon system.
The distance between Earth and the moon is roughly 383,000 km (238,000 mi).
The moon is only visible from Earth when it reflects sunlight.
Only one side of the moon, often called the near side, faces Earth.
The moon rotates once on its axis for every 28.5 days it takes to revolve around Earth.

8. It’s Just a Phase! Unit 3 Lesson 2 Moon Phases and Eclipses
DRAW AND LABEL THE PHASES OF THE MOON.
As the moon revolves around Earth, the portion of the moon that reflects sunlight back to Earth changes.
The lunar phases are changes in the moon’s appearance due to its position in orbit around Earth.
Lunar phases cycle monthly and begin with a new moon.
The new moon is hard to see because Earth, the moon, and the sun are lined up, making the moon unlit.
As the moon moves in its orbit, it reflects more sunlight, and its crescent shape grows larger.
The moon waxes, or grows, until half of the near side is in sunlight. This is the first quarter.
The gibbous phase is when the near side is more than half-lit but not fully lit.
When the moon is fully lit, it is called a full moon.
The lit portion of the moon shrinks, or wanes, during the third week of the cycle.
When the near side is only half-lit in sunlight, it is three-quarters through the cycle. The phase is called the third quarter.
When the moon is seen as waning crescent shapes, the cycle is almost complete.
When the moon is again unlit as a new moon, the cycle is complete.

9. Unit 3 Lesson 2 Moon Phases and Eclipses
Exploring Eclipses
Eclipse – an event during which one object in space casts a shadow on another object
Umbra – darkest part of a shadow
Penumbra – around the umbra a spreading cone of lighter shadow

10. Unit 3 Lesson 2 Moon Phases and Eclipses
Lunar Eclipse
Lunar eclipse occurs when the moon moves through Earth’s shadow
Before a lunar eclipse, the moon is a full moon.
The moon moves into the penumbra shadow and becomes less bright.
When the moon moves into the umbra, the moon is in total darkness.
A total lunar eclipse occurs when the moon moves completely inside the umbra.
If the moon misses all or part of the umbra and a part stays lit, it is called a partial lunar eclipse.
You do not see lunar eclipses each month because the moon’s orbit is tilted by about 5° relative to Earth’s orbit.

11. Unit 3 Lesson 2 Moon Phases and Eclipses
Solar Eclipse
When the moon is directly between the sun and Earth, the shadow of the moon falls on “part” of Earth
When the sun’s light is completely blocked by the moon, it is a total solar eclipse.
Outside the umbra, but within the penumbra, people see a partial solar eclipse.
The moon’s umbra makes a shadow that is never more than a few hundred kilometers across.
A total eclipse covers only a part of Earth and can only be seen in particular areas.
A total solar eclipse happens somewhere on Earth every one to two years.

12. A Rising Tide of Interest
Unit 3 Lesson 3 Earth’s Tides
A Rising Tide of Interest
Tides – daily changes in the level of ocean water due to the difference in the gravitational force of the sun and mostly moon across Earth
The difference in gravitational force is called the tidal force.
Because the moon is closer to Earth, the moon is mainly responsible for Earth’s tides.
Water on the side of Earth closest to the moon bulges toward the moon.
A bulge is created on both the near side and the far side of Earth.
High tide is a water level that is higher than the average sea level.
Low tide is a water level that is lower than the average sea level.
Tidal bulges move around Earth following the motion of the moon.
The moon’s tidal force is greater than the sun’s tidal force, which results in different tidal ranges.
A tidal range is the difference between the levels of ocean water at high tide and low tide.

13. Unit 3 Lesson 3 Earth’s Tides
Tide Me Over
Spring Tides – have the largest daily tidal range, happens when the sun, moon, & Earth form a straight line.
Spring tides happen during the new moon and full moon phases every 14 days.
Why do the tides bulge on both sides of the Earth?
Too often textbooks try to toss off the tides question with a superficial analysis that ignores some things that are absolutely essential for a proper understanding. These include:
Failure to define the specific meaning of "tide".
Failure to properly define and properly use the terms "centripetal" and "centrifugal".
Failure to say whether the analysis is being done in a non-inertial rotating system.
Failure to warn the student that the force diagrams are different depending on whether the plane of the diagram is parallel to, or perpendicular to, the plane of the moon's orbit. If continents are shown on the Earth, that's a clue. If part of the orbit of the moon is shown, that tells you that the diagram is in its orbital plane. But do students always notice these details?
Neglect of tensile properties of solid and liquid materials.
Neglecting to mention that liquid under stress physically moves toward a lower-stress configuration.
Failure to specify the baseline Earth shape against which a tide height is measured.

14. Unit 3 Lesson 3 Earth’s Tides
Neap Tides – smallest daily tidal range, happen when the sun, moon, & Earth form a 90˚ angle.
Neap tides are tides that have the smallest daily tidal range.
Neap tides happen when the sun, moon, and Earth form a 90° angle.
During a neap tide, the gravitational effects of the sun and moon on Earth do not add together.
The moon revolves around Earth much more slowly than Earth rotates.
A place on Earth facing the moon takes 24 h and 50 min to rotate to face the moon again.
So, the cycle of high tides and low tides at that place happens 50 min later each day.
Because the tidal cycle occurs in 24 h and 50 min intervals, it takes about 6 h and 12.5 min for water in an area to go from high tide to low tide.
It takes about 12 h and 25 min to go from one high tide to the next high tide.
Organisms living along coastlines must be able to survive at both high tide and low tide.
Barnacles must survive the differences in water level and temperatures during tidal cycles.
Starfish live in tidal pools where water remains during low tide.
Ghost crabs scurry to avoid being underwater at high tide.