The Sun, Day, and Night - Second Grade Science
Every morning, the sky brightens with golden rays of light as the Sun appears to rise above the eastern horizon. All day long, the Sun glides across the dome of the sky, warming the earth and casting moving shadows, until it sinks below the western horizon at dusk. Then, the world turns dark, revealing the Moon and thousands of distant twinkling stars. For thousands of years, humans believed the Sun circled around Earth. Today we know the truth: Earth is constantly spinning like a giant merry-go-round, creating the regular pattern of day and night!
The Sun: Our Local Star
The Sun is not a solid planet made of rock; it is an enormous, glowing ball of super-heated hydrogen and helium gas called a star.
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| OUR VITAL SUN |
| |
| - SIZE: More than one million Earths could fit inside the Sun! |
| - DISTANCE: Located 93 million miles (150 million km) from Earth. |
| - SPEED OF LIGHT: Sunlight takes about 8 minutes to travel to Earth.|
| - LIFE-GIVER: Provides the heat and light that powers all life! |
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Safety Note: Protecting Your Eyes
The Sun produces blinding light and ultraviolet radiation. NEVER look directly at the Sun with your eyes, through sunglasses, or with binoculars or telescopes! Looking directly at the Sun can cause permanent eye damage or blindness.
Earth's Rotation: Spinning on an Axis
Earth rotates (spins) smoothly on an imaginary center rod called its axis, which runs from the North Pole to the South Pole.
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| HOW ROTATION CREATES DAY & NIGHT |
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| North Pole |
| | |
| Light Rays / \ |
| =========> [ DAY ] | | [ NIGHT ] |
| =========> Facing Sun | | In Shadow |
| =========> \ / |
| From Sun | |
| South Pole |
| |
| Earth completes ONE full spin on its axis every 24 HOURS (1 day)! |
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Facing the Light: Daytime
Because Earth is a solid sphere, the Sun can only illuminate one half of the planet at a time. As Earth rotates from west to east, the side facing the Sun receives direct light and experiences daytime.
Facing the Dark: Nighttime
The half of Earth turned away from the Sun rests in its own shadow, experiencing darkness and nighttime. As Earth continues to spin, regions rotate smoothly out of darkness into the morning light (sunrise) and later rotate out of light into evening shadow (sunset).
The Apparent Motion of the Sun
When you ride in a car, trees and telephone poles seem to race backward past your window, even though they are standing still. The same optical illusion happens with the Sun!
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| APPARENT PATH OF THE SUN ACROSS SKY |
| |
| NOON (Highest Point) |
| \ | / |
| -- O -- |
| / | \ |
| MORNING EVENING |
| \ | / \ | / |
| -- O -- -- O -- |
| (East Horizon) (West Horizon) |
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| The Sun SEEMS to move because Earth is rotating beneath our feet! |
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East to West Movement
Because Earth rotates toward the east, the Sun appears to rise in the east, travel across the southern sky, and set in the west. The Sun is not actually flying across our sky; our planet is turning beneath our feet!
How Shadows Change Throughout the Day
A shadow forms when an opaque object blocks light from passing through. Because the Sun's position in the sky appears to change from morning to night, shadows change in predictable ways.
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| DAILY SHADOW PATTERNS |
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| TIME OF DAY SUN POSITION SHADOW LENGTH & DIRECTION |
| Early Morning Low in the East Long shadow pointing West |
| Midday / Noon High Overhead (South) Shortest shadow of the day |
| Late Afternoon Low in the West Long shadow pointing East |
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The Sundial: Telling Time by Shadows
Before mechanical clocks or wristwatches were invented, ancient civilizations told time using sundials. A sundial has a vertical pointer called a gnomon that casts a shadow onto a marked dial plate. As the Earth rotates, the shadow slowly swings across the hour marks!
Chapter Review Exercises
Question 1: What causes the daily cycle of day and night on planet Earth?
Question 2: How long does it take for Earth to complete one full rotation on its axis?
Question 3: Why does the Sun appear to rise in the east and set in the west each day?
Question 4: Describe how the length and direction of your shadow changes between 8:00 AM and 12:00 PM (noon).
Solutions and Explanations
Solution 1: Day and night are caused by Earth's rotation on its axis. As Earth spins, the half facing the Sun experiences daylight, while the opposite half turned away in shadow experiences darkness and nighttime.
Solution 2: It takes Earth 24 hours (exactly one day) to complete one full rotation on its axis.
Solution 3: The Sun appears to rise in the east and set in the west because Earth rotates from west to east. This spinning motion creates the optical illusion that celestial objects are traveling across the sky in the opposite direction.
Solution 4: At 8:00 AM, the Sun is low in the eastern sky, casting a very long shadow that points toward the west. By 12:00 PM (noon), the Sun has climbed to its highest point overhead, making your shadow short and pointing roughly north.