# The Changing Moon

Look up at the night sky and you'll see the Moon—Earth's only natural satellite and our closest celestial neighbor. But if you look night after night, you'll notice something strange: the Moon seems to change shape!

Sometimes it's a thin crescent. Sometimes it's a perfect circle. Sometimes it seems to disappear entirely. What causes these changes?

Common Misconception: Many people think Earth's shadow causes Moon phases. This is NOT correct!

In this lesson, you'll discover the real reason for Moon phases, learn how the Moon creates ocean tides, and explore the spectacular events we call eclipses.

Essential Question: Why does the Moon appear to change shape?

# Moon Basics

## Facts About Our Moon

| Property | Value | |----------|-------| | Distance from Earth | ~384,400 km (about 30 Earth diameters away) | | Diameter | 3,474 km (about 1/4 of Earth's) | | Orbital period | ~27.3 days to orbit Earth | | Synodic period | ~29.5 days (full cycle of phases) | | Surface gravity | 1/6 of Earth's (you'd weigh 1/6 as much!) | | Rotation | Tidally locked (same side always faces Earth) | | Atmosphere | None (no weather, no sound) | | Temperature range | -173°C (night) to 127°C (day) |

## Key Concepts

The Moon does NOT produce its own light! The Moon is a rock. We see it because it reflects sunlight, just like how you can see a ball in a dark room if you shine a flashlight on it.

Half the Moon is ALWAYS lit by the Sun. At any given moment, the half of the Moon facing the Sun is illuminated. The half facing away is dark. This never changes.

What changes is how much of the LIT side we can see from Earth. As the Moon orbits Earth, we see different portions of its illuminated half—and that's what creates the phases!

# The Eight Moon Phases

## Why Do We See Phases?

Imagine standing in a room with a bright lamp (the Sun). You hold a ball (the Moon) and slowly walk around your head (Earth). As you move the ball: - When the ball is between you and the lamp, you see the dark side (New Moon) - When you're between the ball and lamp, you see the fully lit side (Full Moon) - In between, you see partial illumination (the other phases)

KEY INSIGHT: The Moon's phases are caused by its changing POSITION relative to Earth and the Sun—NOT by Earth's shadow!

## The Eight Phases (In Order)

Waxing = Getting bigger (lit portion increasing) Waning = Getting smaller (lit portion decreasing)

| Phase | Appearance | When It Rises | Position | |-------|------------|---------------|----------| | 1. New Moon | Completely dark | Sunrise | Between Earth and Sun | | 2. Waxing Crescent | Right sliver lit | Morning | Moving away from Sun | | 3. First Quarter | Right half lit | Noon | 90° from Sun | | 4. Waxing Gibbous | Mostly lit (right) | Afternoon | Approaching opposite side | | 5. Full Moon | Completely lit | Sunset | Opposite Sun from Earth | | 6. Waning Gibbous | Mostly lit (left) | Evening | Moving toward Sun | | 7. Third Quarter | Left half lit | Midnight | 90° from Sun (other side) | | 8. Waning Crescent | Left sliver lit | Before sunrise | Almost back to New Moon |

Memory trick: "DOC" - In the Northern Hemisphere: - D shape (right side lit) = waxing (getting bigger) - O shape (full) = full moon - C shape (left side lit) = waning (getting smaller)

# Moon and Tides

## How the Moon Creates Tides

The Moon's gravity pulls on Earth. This gravitational pull is strongest on the side of Earth closest to the Moon and weakest on the side farthest away.

This creates a "bulge" in Earth's oceans: - One bulge on the side closest to the Moon (pulled toward Moon) - Another bulge on the opposite side (Earth pulled away from water)

As Earth rotates through these bulges (every ~24 hours), coastal areas experience: - High tide: When in a bulge (water is higher) - Low tide: When between bulges (water is lower)

Most coastal areas have two high tides and two low tides each day!

## Spring Tides and Neap Tides

The Sun also affects tides (though less than the Moon due to distance).

Spring Tides (Extra High and Extra Low) - Occur during New Moon and Full Moon - Sun, Moon, and Earth are aligned - Gravitational forces ADD together - Highest high tides, lowest low tides

Neap Tides (Moderate) - Occur during First and Third Quarter - Sun and Moon are at right angles - Gravitational forces partially CANCEL - Less extreme tides

# Solar and Lunar Eclipses

## What is an Eclipse?

An eclipse occurs when one celestial body blocks light from reaching another. There are two types involving Earth, Moon, and Sun.

## Solar Eclipse

What happens: The Moon passes between Earth and Sun, blocking sunlight.

When it occurs: Only during New Moon (Moon between Earth and Sun)

What you see: Moon's shadow falls on Earth; the Sun appears blocked out

Types: - Total: Moon completely covers Sun (spectacular! corona visible) - Partial: Moon only partly covers Sun - Annular: Moon too far from Earth, leaves a "ring of fire"

Safety: NEVER look directly at a solar eclipse without special eclipse glasses!

## Lunar Eclipse

What happens: Earth passes between Sun and Moon, blocking sunlight from reaching Moon.

When it occurs: Only during Full Moon (Earth between Sun and Moon)

What you see: Earth's shadow falls on Moon; Moon turns reddish-orange ("blood moon")

Why reddish: Earth's atmosphere bends red light onto the Moon

Safety: Safe to watch with naked eyes—you're looking at the Moon, not the Sun

## Why Eclipses Don't Happen Every Month

The Moon's orbit is tilted about 5° compared to Earth's orbit around the Sun. Most months, the Moon passes slightly above or below the direct line between Earth and Sun. Eclipses only occur when everything aligns precisely.

# Summary

## Key Concepts Review

Moon Phases: - The Moon reflects sunlight (doesn't make its own light) - Half the Moon is always lit; phases show how much WE see - Caused by Moon's position relative to Earth and Sun—NOT Earth's shadow - Complete cycle: ~29.5 days

The Eight Phases (in order): New Moon → Waxing Crescent → First Quarter → Waxing Gibbous → Full Moon → Waning Gibbous → Third Quarter → Waning Crescent → (repeat)

Tides: - Caused by Moon's (and Sun's) gravitational pull on oceans - Most coasts have 2 high tides and 2 low tides per day - Spring tides (extreme): New Moon and Full Moon - Neap tides (moderate): Quarter Moons

Eclipses: - Solar: Moon blocks Sun (New Moon, wear protection!) - Lunar: Earth's shadow on Moon (Full Moon, safe to view)