# Unit Review: Earth's Place in the Universe

This review covers everything we learned about the Earth-Sun-Moon system. Use it to prepare for your unit assessment.

## Topic 1: Our Cosmic Address & the Solar System

Your Cosmic Address (small to large): Earth → Solar System → Milky Way Galaxy → Local Group → Observable Universe

The Solar System: - The Sun contains 99.8% of all mass in our solar system - 8 planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune - Terrestrial (Rocky): Mercury, Venus, Earth, Mars, small, dense, solid surfaces - Gas Giants: Jupiter, Saturn, large, no solid surface, hydrogen/helium - Ice Giants: Uranus, Neptune, icy materials, smaller atmospheres

The Goldilocks Zone (Habitable Zone): - The region around a star where liquid water can exist on a planet's surface - Earth supports life because of: liquid water, breathable atmosphere (78% N₂, 21% O₂), protective magnetic field, and right size/gravity

## Topic 2: Seasons & Earth's Axial Tilt

MYTH BUSTED: Seasons are NOT caused by Earth's distance from the Sun. Earth is actually closest to the Sun in January!

The Real Cause: Earth's 23.5° axial tilt creates a double effect: 1. Changes the angle of sunlight (direct = concentrated = warmer; angled = spread out = cooler) 2. Changes the number of daylight hours

The Four Key Positions: - Summer Solstice (~June 21): Longest day, North tilts toward Sun, ~14.5 hrs daylight in NC - Fall Equinox (~Sept 22): Day ≈ night (~12 hrs), fall begins - Winter Solstice (~Dec 21): Shortest day, North tilts away, ~9.5 hrs daylight in NC - Spring Equinox (~March 20): Day ≈ night (~12 hrs), spring begins

Opposite Hemispheres: When it's summer in the Northern Hemisphere, it's winter in the Southern Hemisphere.

## Topic 3: Moon Phases

Key Facts: - The Moon does NOT produce its own light. It reflects sunlight - Half the Moon is ALWAYS lit by the Sun - Phases are caused by the Moon's changing position relative to Earth and the Sun, NOT by Earth's shadow

The Eight Phases (in order): 1. New Moon (completely dark) 2. Waxing Crescent (right sliver) 3. First Quarter (right half) 4. Waxing Gibbous (mostly lit, right) 5. Full Moon (completely lit) 6. Waning Gibbous (mostly lit, left) 7. Third Quarter (left half) 8. Waning Crescent (left sliver)

Memory trick: D-O-C: D shape = waxing, O = full, C shape = waning Waxing = getting bigger; Waning = getting smaller

## Topic 4: Tides & Eclipses

Ocean Tides: - Caused by the Moon's (and Sun's) gravitational pull on Earth's oceans - Two bulges create 2 high tides and 2 low tides per day - Spring tides (extreme): New Moon & Full Moon, forces aligned - Neap tides (moderate): Quarter Moons, forces at right angles

Eclipses:

| Feature | Solar Eclipse | Lunar Eclipse | |---------|--------------|---------------| | What blocks light? | Moon blocks Sun | Earth blocks sunlight to Moon | | Moon phase | New Moon | Full Moon | | Eye safety | REQUIRES protection | Safe to view | | Duration | Minutes | Hours |

Eclipses don't happen every month because the Moon's orbit is tilted ~5° from Earth's orbital plane.

## Topic 5: Moons of Our Solar System

Moon counts: Mercury (0), Venus (0), Earth (1), Mars (2), Jupiter (97), Saturn (274), Uranus (29), Neptune (16)

Giant planets have many moons because of their strong gravity.

Remarkable moons: - Io (Jupiter): extremely active volcanoes - Europa (Jupiter): icy crust, evidence for subsurface ocean - Ganymede (Jupiter): largest moon in the Solar System - Titan (Saturn): thick atmosphere, liquid methane lakes - Enceladus (Saturn): ice geysers

Tidal locking: The Moon rotates once per orbit, keeping the same face toward Earth. The far side is NOT always dark. It gets sunlight too.