Why Charlotte Doesn't Freeze in June: Seasons & Earth's Tilt
Understanding How a 23.5° Tilt Creates Four Seasons
Learning Objectives
Explain that Earth's axis is tilted at 23.5° relative to its orbital plane and that this tilt — not distance from the Sun — is the primary cause of seasons.
Describe how axial tilt causes one hemisphere to receive more direct sunlight (higher intensity, longer days) during its summer and less direct sunlight (lower intensity, shorter days) during its winter.
Predict the season in one hemisphere when given the season in the opposite hemisphere, and explain why they are reversed.
Use a model (diagram or physical demonstration) to show how the angle of sunlight striking Earth's surface changes with axial tilt and explain how this affects temperature.
Hook & Vocabulary
~5 minutesHere's a fact that breaks most people's brains: Earth is actually closer to the Sun in January than in July. Read that again. In the dead of winter — when Charlotte is shivering through 35°F mornings — our planet is about 3 million miles closer to the Sun than it is during our hottest summer days. So if distance doesn't cause seasons... what does?
Seasons are caused by the tilt of Earth's axis — a 23.5° lean that never changes direction as Earth orbits the Sun. This tilt determines which hemisphere gets more direct sunlight at any given time of year.
Before we watch the video, let's lock in the vocabulary you'll need. These aren't just definitions to memorize — they're the building blocks of the model you'll construct in your head today.
An imaginary straight line that passes through Earth from the North Pole to the South Pole. Earth spins (rotates) around this line once every 24 hours, giving us day and night. The critical detail: this axis isn't straight up and down — it's tilted 23.5° from vertical.
Earth spinning on its own axis. One full rotation = one day (24 hours). Rotation gives us the cycle of day and night. Think of it like a basketball spinning on a fingertip.
Earth traveling around the Sun in a nearly circular path. One full revolution = one year (365.25 days). Revolution combined with axial tilt is what produces the seasonal cycle. Think of it like walking in a big circle around a campfire — rotation is you spinning, revolution is you walking the circle.
One half of Earth, divided by the equator. The Northern Hemisphere includes North America, Europe, and most of Asia. The Southern Hemisphere includes most of South America, Africa below the equator, and Australia. Charlotte, North Carolina sits at about 35°N latitude — solidly in the Northern Hemisphere.
Direct sunlight hits Earth's surface at a steep angle (close to 90°), concentrating energy in a small area — this makes it feel hotter. Indirect sunlight hits at a shallow angle, spreading the same energy over a larger area — this makes it feel cooler. The tilt of Earth's axis determines which parts of the planet receive direct vs. indirect sunlight at different times of year.
The two days each year when Earth's axial tilt points most directly toward or away from the Sun. The summer solstice (around June 21) is the longest day of the year in the Northern Hemisphere — Charlotte gets about 14 hours and 35 minutes of daylight. The winter solstice (around December 21) is the shortest — Charlotte gets only about 9 hours and 45 minutes. That's a difference of nearly 5 hours!
The two days each year when Earth's axis tilts neither toward nor away from the Sun, and day and night are approximately equal in length everywhere on Earth (about 12 hours each). The vernal (spring) equinox occurs around March 20, and the autumnal (fall) equinox around September 22. The word comes from Latin: aequus (equal) + nox (night).
The amount of light energy hitting a given area of surface. Higher intensity = more energy = warmer temperatures. When the Sun is high in the sky (direct sunlight), light intensity is high. When the Sun is low in the sky (indirect sunlight), intensity is low because the same light spreads over more ground.
Video & Observation
~10 minutesNow let's watch the Generation Genius video on the Causes of Seasons. As you watch, pay attention to three things: (1) what the 23.5° tilt actually looks like, (2) how sunlight hits the Northern vs. Southern Hemisphere differently at different points in Earth's orbit, and (3) why the equator stays warm year-round.
1. The video shows Earth at four positions in its orbit. Try to identify which position is summer in the Northern Hemisphere and which is winter. 2. Watch for the flashlight demonstration — notice how the same beam of light covers MORE area when it hits a surface at an angle. 3. Listen for why Australia's seasons are opposite to ours. Be ready to explain this in your own words.
Post-Video Exploration & Connection
~7 minutesAfter the Video
Grab a flashlight (or use your Chromebook's screen on full white brightness) and a flat surface like your desk. Step 1: Hold the flashlight directly above the desk pointing straight down. Notice the bright, concentrated circle of light — this represents direct sunlight (summer). Step 2: Now tilt the flashlight at a steep angle, keeping the same distance. The light spreads into a wide oval and is dimmer at any single point — this represents indirect sunlight (winter). The key insight: The flashlight didn't change — the angle did. The Sun doesn't get brighter in summer. The angle at which sunlight hits your part of Earth changes because of the tilt.
Let's bring this home to Charlotte. On the summer solstice (around June 21), the Sun climbs to about 78.5° above the horizon at noon — nearly straight overhead. Shadows are short. Sunlight is intense. We get almost 15 hours of daylight. On the winter solstice (around December 21), the Sun only reaches about 31.5° above the horizon at noon — low in the sky. Shadows are long. Sunlight is spread thin. We get under 10 hours of daylight. Same Sun. Same distance. The only thing that changed? Which way Earth's axis was pointing.
Most adults — including many college students — incorrectly believe that seasons are caused by Earth being closer to or farther from the Sun. This is wrong. Earth's orbit is nearly circular, and in fact Earth is closest to the Sun in early January (Northern Hemisphere winter). The real cause is the 23.5° axial tilt, which changes the angle and duration of sunlight each hemisphere receives. If you remember nothing else from today, remember this.
Earth's 23.5° axial tilt is the single most important fact about seasons. As Earth revolves around the Sun, this tilt causes each hemisphere to alternate between receiving more direct sunlight (summer) and less direct sunlight (winter). More direct sunlight means higher intensity, longer days, and warmer temperatures. The axis always points the same direction in space — it's Earth's position in its orbit that determines which hemisphere leans toward the Sun.
Check Your Understanding
~5 minutesWhat is the PRIMARY cause of seasons on Earth?
During summer in the Northern Hemisphere, what TWO things happen to the sunlight reaching places like Charlotte, NC?
A student shines a flashlight straight down onto a desk and sees a small, bright circle. Then they tilt the flashlight at an angle and see a large, dim oval. What does this model demonstrate about seasons?
If it is July and students in Charlotte, NC are on summer break, what season is it for students in Sydney, Australia?
Earth is closer to the Sun during summer in the Northern Hemisphere, which is why summer is warmer.
Earth's axis always points in the same direction in space as Earth orbits the Sun — the tilt doesn't wobble back and forth throughout the year.
Match each event or date to the correct description of what is happening on Earth.
Place these events in the correct order as experienced in Charlotte, NC, starting from the LONGEST day and moving through the year.
Earth's axis is tilted at ___1___ degrees from vertical. One complete rotation of Earth takes ___2___ hours, and one complete revolution around the Sun takes about ___3___ days. On the summer solstice, Charlotte receives approximately ___4___ hours of daylight.
Deeper Thinking
~3 minutesYour friend says: 'Summer is hot because Earth moves closer to the Sun.' Write a 2–4 sentence response explaining why your friend is wrong and what actually causes summer to be warmer. Use at least two vocabulary words from today's lesson.
Expected length: 2-4 words
Imagine Earth had NO axial tilt — the axis was perfectly straight up and down (0°). Describe what would happen to the seasons. Would Charlotte still experience summer and winter? What about the equator — would it change? Explain your reasoning.
Expected length: 3-5 words