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Explore the concept of day and night and investigate the relationship between Earth's rotation and the Sun. Learn about the causes of day and night, the Earth's axis, and the duration of Earth's rotation and revolution.
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Investigation 2part 2 Earth/sun relationship
Hello darkness, my old friend • Have you ever thought, “What is night?” • Write at least 2 sentences answering: • What causes night?
What is night, and what causes it? • What are some ideas?
What is day, and what causes it? • What are some ideas?
Focus question • What causes day and night? • DO NOT answer at this time.
Lamp as a model • Is there any way we could use this lamp to test some of your ideas about day and night?
Day/night movements • Which statements explain day and night most effectively? Can we add or refine?
Challenges • Rotate so that your observer is experiencing day, then night. • Rotate so that your observer is experiencing noon. • Rotate so that your observer is experiencing midnight. • Rotate so that your observer is experiencing sunrise. • Rotate so that your observer is experiencing sunset.
Earth’s rotation • Which way does Earth rotate? • Clockwise or counterclockwise?
modeling • Daytime • Nighttime • Noon • Midnight • Sunrise • Sunset
Notebook entry • Make a diagram showing Earth’s rotation. • Label the rotation and axis and a short explanation.
Demonstration with globe • How should I set up the model? Where should the Sun be, and where should Earth be?
Why is it dark at night? • At any given time, how much of Earth is in daylight and how much is in darkness? • What makes the Sun “come up” and “go down”? • Does the Sun come up in the morning all over the world? Explain.
Key points • The Sun is aluminous object that gives off light. The Sun is a source of light that illuminates Earth during the day. • When light falls on an object, the portion in the path of the light is illuminated. The area behind the object is in the shadow, in the dark. • When light falls on a spherical object, like a planet, exactly half is in the light and half is in the dark.
Key points continued • The dark side of the sphere is in its own shadow, not the shadow of another object. • Day and night are the names given to the light and dark halves of a planet. • The Sun is stationary (essentially) and Earth rotates on its axis once every day, giving the illusion of a Sun that rises and sets.
Key points continued • If a planet didn’t rotate, it would have a day side and a night side just the same as a planet that does rotate. The difference is that, when a planet rotates, the part of the planet experiencing day and the part experiencing night changes continually; if a planet didn’t rotate, one half would experience day all the time, and one half would experience night all the time. • One complete rotation of our planet accounts for one complete day. For Earth, one rotation requires 24 hours (1 day).
question • How does Earth move relative to the Sun?
Next question • How long does it take Earth to make one revolution around the Sun?
Earth’s axis • How long does it take for Earth to rotate (turn around once) on its axis?
North star • Named Polaris • North Pole points toward Polaris due to the 23.5° tilt of Earth.
Key points • Earth is tilted 23.5° on its axis, and the axis always points in the same direction, toward the North Star. • One rotation of Earth takes 24 hours, producing the day/night cycle on Earth. • Earth revolves around the Sun in a circular orbit once every 365.25 days.
