Moon Phases & Rotation and Revolution

Earth, Sun, & Moon System

Learning Objectives

• Define Earth's rotation (day/night) and revolution (year).

• Explain how Earth's tilt causes seasons and varied day length.

• Define gravity, mass, weight, inertia; explain orbital motion.

• Explain moon phases and eclipses (causes, shadows, frequency).

• Earth spins on its axis, an imaginary line through the poles.

• It rotates from west to east.

• One complete spin takes about 24 hours (one day).

• This spinning causes the cycle of day and night.

What is Earth's Rotation?

Multiple Choice

What is the primary effect of Earth's rotation on its axis?

• The change of seasons

• The cycle of day and night

• The phases of the moon

• The occurrence of eclipses

• Revolution is Earth's yearly journey around the Sun.

• Earth follows an oval-shaped path called an orbit (ellipse).

• One complete revolution takes about 365.25 days, defining our year.

• Due to the ellipse, Earth is closest to the sun in January.

What is Earth's Revolution?

Multiple Choice

How long does it take Earth to complete one revolution around the sun?

• About 24 hours

• About 29.5 days

• About 365.25 days

• About 1 month

• Earth's axis is tilted at a 23.5-degree angle.

• This tilt stays fixed as Earth orbits the Sun.

• Tilting towards the Sun brings direct sunlight and summer.

• Tilting away brings less direct sunlight and winter.

Earth's Tilt Causes Seasons

Multiple Choice

What is the main reason Earth experiences seasons?

• Earth's distance from the sun changes significantly

• Earth rotates on its axis

• Earth's axis is tilted as it revolves around the sun

• The sun's energy output changes

• Earth's tilt changes the angle sunlight hits different places.

• Near the equator, direct sunlight concentrates heat, making it warmer.

• Near the poles, angled sunlight spreads heat, making it cooler.

• Without tilt, sunlight angles wouldn't change much, meaning no seasons.

Sunlight Angle and Seasons

Multiple Choice

Why is it generally warmer near the equator than near the poles?

• The equator is closer to the sun

• Sunlight hits the equator more directly, concentrating heat

• The poles are always tilted away from the sun

• The equator rotates faster

• Earth's tilt changes daylight hours. More tilt toward sun = longer days.

• Solstices: Max tilt toward/away from sun. Longest/shortest days (~June 21/Dec 22 N.Hem).

• Equinoxes: No tilt toward sun. Sun directly over equator at noon.

• Day and night are nearly equal (~12 hrs). Occur ~March 21 & Sept 22.

Day Length, Solstices & Equinoxes

Multiple Choice

What happens during an equinox?

• One hemisphere experiences its longest day

• One hemisphere experiences its shortest day

• Neither hemisphere is tilted directly towards the sun, and day/night are nearly equal

• Earth is closest to the sun

• Gravity pulls any two objects with mass toward each other.

• More mass means stronger gravity pull between objects.

• More distance means weaker gravity pull between objects.

• Gravity keeps planets orbiting the sun and moons orbiting planets.

What is Gravity?

Multiple Choice

According to Newton's Law of Universal Gravitation, the strength of gravity between two objects depends on what two factors?

• Their speed and direction

• Their temperature and color

• Their masses and the distance between them

• Their volume and density

• Mass is how much matter (stuff) is in an object. It never changes!

• Weight is gravity's pull on an object's mass. It changes with location.

• Your mass stays the same, but you weigh less on the Moon (less gravity).

• Astronauts in orbit feel weightless because they are constantly falling around Earth.

What's the Difference: Mass vs. Weight?

Multiple Choice

If an astronaut travels from Earth to the Moon, what happens to their mass and weight?

• Mass decreases, weight stays the same

• Mass stays the same, weight decreases

• Both mass and weight decrease

• Both mass and weight stay the same

• Inertia resists changes in an object's motion.

• Objects keep doing what they are doing unless a force acts.

• More mass means more inertia; harder to move or stop.

• Your body moves forward in a braking car due to inertia.

What is Inertia?

Multiple Choice

What is inertia?

• The force of gravity on an object

• The speed of an object in orbit

• The tendency of an object to resist changes in motion

• The amount of matter in an object

• Inertia makes objects want to travel straight.

• Gravity pulls orbiting objects inward toward the center.

• Gravity bends the straight path into a curved orbit.

• Orbiting is a balance between inertia and gravity.

Why Things Orbit: Gravity and Inertia

Multiple Choice

What two factors combine to keep the Moon in orbit around Earth?

• Mass and Weight

• Rotation and Revolution

• Gravity and Inertia

• Solstices and Equinoxes

• Moon phases are how the Moon looks from Earth.

• Caused by changing angles of sunlight hitting the Moon.

• We see different parts of the Moon's always sunlit half.

• A full cycle of phases takes about 29.5 days.

What Are Moon Phases?

Multiple Choice

What causes the different phases of the moon as seen from Earth?

• Earth casting a shadow on the Moon

• The Moon moving into the Sun's shadow

• The Moon producing its own light in cycles

• Changing angles between the Sun, Earth, and Moon as the Moon orbits Earth

• Eclipses happen when one body blocks light from another.

• Sun, Earth, Moon must align. Solar=Moon blocks Sun. Lunar=Earth blocks Moon.

• The Moon's path around Earth is tilted about 5 degrees.

• This tilt means alignment is rare, not every month.

Eclipses: What & Why Not Monthly?

Multiple Choice

Why don't solar and lunar eclipses happen every month during the new and full moons?

• The Sun's position changes too much

• The Moon's speed varies too much

• The Moon's orbit is tilted relative to Earth's orbit

• Earth's tilt changes throughout the month

• Moon passes directly between the Sun and Earth.

• The Moon casts its shadow onto part of Earth.

• Solar eclipses happen only during a New Moon.

• The Sun appears blocked; the corona may be visible.

Solar Eclipses

Multiple Choice

During which phase of the moon can a solar eclipse occur?

• Full Moon

• First Quarter

• New Moon

• Third Quarter

• Earth moves between the Sun and the Moon.

• ​Earth's shadow blocks sunlight from reaching the Moon.

• Lunar eclipses happen only during a Full Moon.

• The Moon looks dim and can turn reddish.

What is a Lunar Eclipse?

Multiple Choice

What happens during a lunar eclipse?

• The Moon blocks the Sun's light from reaching Earth

• Earth blocks sunlight from reaching the Moon

• The Sun blocks the Moon's light from reaching Earth

• The Moon passes into the Sun's shadow

• Eclipses involve two shadow parts: the umbra and penumbra.

• Umbra: Darkest center, totally blocks the Sun, causes total eclipses.

• Penumbra: Lighter outer shadow, partially blocks Sun, causes partial eclipses.

• Moon casts these on Earth (solar); Earth casts these on Moon (lunar).

Shadows in Space: Umbra & Penumbra

Multiple Choice

What is the umbra?

• The area where a partial eclipse is seen

• The darkest part of a shadow where light is completely blocked

• The tilt of the Moon's orbit

• The faint outer atmosphere of the Sun

​Correction

• Earth's changing distance from the Sun causes seasons.

• The Moon makes its own light.

• Eclipses happen every single month.

• Mass and weight are the exact same thing.
  

​Misconception

Common Misconceptions

• Earth's tilt causes seasons by changing sunlight intensity.

• The Moon only reflects light from the Sun.

• The Moon's tilted orbit prevents monthly perfect alignment.

• Mass is matter amount; weight is gravity's pull.
  

Summary

• Earth rotates daily (day/night) and revolves yearly around the Sun.

• Earth's 23.5° axis tilt causes the seasons as it revolves.

• Gravity pulls objects together; inertia keeps them moving in orbit.

• Moon phases and eclipses depend on Sun, Earth, Moon positions.

Open Ended

Briefly explain the difference between Earth's rotation and revolution.

Poll

What is the main cause of Earth's seasons?

• Changing distance to sun

• Earth's rotation speed

• Earth's axial tilt

• Volcanic activity

Open Ended

Which force keeps the Moon orbiting Earth instead of flying off in a straight line?

Poll

How confident are you in explaining why seasons occur? (Rate 1-4, 4=Very Confident)

• 1

• 2

• 3

• 4

Open Ended

What topic from today's review lesson was most confusing or needs more clarification?