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PPS Sci8 - Earth in Space - Week 2 - What causes Day and Night?

By Susan Holveck
Last updated about 4 years ago
38 Questions
Note from the author:
This week, students continue to look for patterns in the day-night cycle on Earth and look at what causes these phenomena. Students also continue to work on modeling concepts. What causes the shadows to move? Why do we have day and night? How can we model these concepts?

Earth in Space: Week 2


Learning Targets for this formative:
  • I can show understanding of the patterns in the day-night cycle by making models of the Earth and Sun.
  • I can speak and listen during discussion
  • I can read for information.
Guiding Questions for this week:
  • What causes the shadows to move?
  • Why do we have day and night?
  • How can we model these concepts?
1.

Before you begin this formative, how are you feeling?

2.

Set Your Intention

What quality of being a scientist do you want to focus on today during our work? Briefly explain why you chose that one.
  • observant
  • patient
  • good listener
  • communicate well
  • persevere
  • hard working
  • detailed
Example, "I want to make sure I communicate well so my ideas are shared. I think I have good ideas."

Formative Assessment - What do you already know about shadows?
3.

No Shadow
Four friends in New York City were wondering if there was ever a time during the day when they would have no shadow. They each had different ideas about daytime shadows. Which friend do you most agree with?

This is what they said:

4.

Explain why you chose the answer that you did. Explain your thinking.


5.

Me and My Shadow
Five friends were looking at their shadows early one morning. They wondered what their shadows would look like by the end of the day. Which friend do you most agree with?

This is what they said:

6.

Explain why you choose the answer that you did.


Watch this video if you need to refresh your understanding on why shadows move during the day.
7.

Explain the patterns that you see for length and direction of shadows versus time of day in Graph 1 and Graph 2.

The Sun appears to be constantly moving across the sky. How does its path change from month to month? We know that the Sun rises in the east and sets in the west, but does it rise exactly east and set exactly west every day? We also know that the days are longer in the summer and shorter in the winter. But how is it connected with Sun’s changing path across the sky?

These are some common questions we are all confronted with. They become all the more relevant, for example, when we talk about a solar panels’ performance. Life would be very simple if the Sun were to arise and set precisely in the same directions and if it followed exactly same path through the sky everyday throughout the year.


How would the sun's changing position affect a shadow that is cast by an object?

For the diagram below, a wall is casting a shadow. You can see how the shadow changes length for different times of the year (June, March and December)
Predict how the length and direction of a shadow would change in different seasons. Assume it is the same time of day and the same object casting a shadow.
8.

Would the length of a shadow change between summer and winter?

9.

Does the direction that a shadow falls change between the summer and winter?

10.

Explain why you choose the answer that you did for the direction of the shadow. You can use a drawing and writing to explain your ideas.

A Day on Earth

The Sun shines on every planet, but the time from one sunrise to the next - one full day-night cycle- is different for each planet. On Earth, one full day-night cycle lasts 24 hours, one complete day. On average, each day on Earth has about 12 hours in light and 12 hours in darkness. As we have experienced, Winter has less light than Summer. On Jupiter, a day-night cycle takes less than 10 Earth hours.

Have you ever wondered why night and day happen here on Earth, or anywhere else?

Focus Questions:
Your goal should be to provide an answer to the questions by the end of the lesson
  • What causes the day-night cycle?
Modeling Ideas
11.

Formative Assessemnt - What do you already know?

What causes day and night?
  • Draw a picture that shows the Sun and the Earth during the day in the United States.
  • Draw a picture that shows the Sun and the Earth during the night in the United States.

12.

On Earth, day and night are caused by______________.

13.

It is day when______________________.

14.

It is night when______________________.

Watch this video about what causes day and night. Do you want to change any of your answers to the questions above? Do you want to change your model? If you do, please make your changes after the video.
The video above showed a demonstration of a model of the Earth rotating in a day and night cycle. The next video that shows the Earth from space, rotating for one day and night cycle.
Possible Explanations: A Day on Earth
15.

Read each idea below and observe the diagram for the idea. Record your ideas how the diagram might be considered to support or not support the idea.

16.

Read each idea below and observe the diagram for the idea. Record your ideas how the diagram might be considered to support or not support the idea.

Video of Day and Night Cycle. This video is a computer model of the day and night cycle.
17.

How does using models help us understand the day and night cycle?

18.

Put a red circle around the planet that has the shortest day.
Put a green square around the planet that has the longest day.
Put a blue rectangle aro0und the two planets that have the same day length.
Put a yellow circle ar9und the planet that has the length of day that is closest to the Earth's.

19.

Jupiter’s day-night cycle is a little less than 10 hours long. This is very surprising since Jupiter is, by far, the largest planet. It orbits every 11.7 years. What does this tell you about Jupiter’s rotation on its axis?

For fun - watch this video of spending a day on Jupiter. There are stunning pictures of this beautiful planet.
20.

What causes the day-night cycle? Share your ideas. Have they changed?

Although the changing position of the Sun throughout the day makes it look like the sun is moving, you now know that it is the Earth that really moves. The rotation of the Earth around its axis causes the 24-hour cycle of day and night.

Focus Question:
Your goal should be to provide an answer to the questions by the end of the lesson.
  1. What are the properties of the rotation of the Earth?
  2. What effect does the rotation of Earth have on the way people measure time?
Before you read mark whether you agree or disagree with each statement below. It is OK if you do not already know the answer to the question. After the reading you will get a chance to answer the same questions again.
21.

Ancient people used the shadows cast by sticks to indicate the passage of time during the day.

22.

When the sun rises in the western United States, it is still dark in the eastern United States.

23.

Benjamin Franklin divided the world into time zones in the late 1700’s.

24.

The World is divided into 12 time zones.

25.

When it is nighttime in the United States, it is daytime in Asia.

Please read

One Day–Night Cycle is One Complete Rotation of Earth

Every 24 hours, Earth rotates, or turns around its axis. The axis is an imaginary line through the center of Earth, from the North Pole to the South Pole. One complete turn of Earth is called a rotation (row-TAY-shun). You can simulate this movement by slowly spinning a globe on its stand. If you look down onto the North Pole at the top of the globe, you should spin the Earth counterclockwise, as shown in Figure 1.
At sunrise where you live, you see the Sun coming up on the eastern horizon as your region of Earth rotates into the light from the Sun. Then the Sun appears to move across the sky from east to west, until it sets. Figure 2 below shows approximately where the Sun appears in the sky during a typical day in most of the United States in early spring and early fall. In spring and fall, day and night are about equal in length, at 12 hours each.

Using the Sun to Make a Clock

You observed that the shadow from your sun stick moved in the same direction as the hands on a clock, or “clockwise.” You may not have realized it, but your sun stick observations are a lot like methods people used to measure time long ago.
Researchers think that ancient peoples in Africa and the Middle East put sticks into the ground and scratched marks in the ground to track the movement of the shadow cast by the stick. This would have shown the passage of time during the day—that’s just what a clock does.

Eventually, people began to build structures for keeping time. As early as 5,000 years ago, the Egyptians built tall stone towers called obelisks. Some people think they used the obelisks’ shadows to show the time of day. Sometime after that, sundials were invented, probably in many places by different cultures. Although we can’t say for sure who frst invented sundials, the earliest known sundial was found in Egypt and was made about 3,500 years ago.

Like sun sticks, sundials use shadows to indicate the time, as shown in Figure 3. Each sundial has an upright piece that casts a shadow on a disc marked with the hours of the day. The shadow from a stick or on a sundial is shortest at noon, when the Sun is at its highest point in the sky. The direction of the sundial shadow changes just as your sun stick shadow does. In the Northern Hemisphere, the shadow moves across a sundial from morning to night. The clockwise movement of the shadow is no coincidence: inventors arranged the hands and hours on clocks to imitate the movement of the shadow and the hour marks on a sundial. Sundials are no longer used to keep time, but you might see them in special places in gardens and parks.
Earth’s Rotation and Time Zones

Every day in the United States, the Sun shines frst on East Coast cities such as New York and Miami. It takes about three more hours for Earth to rotate enough to move West Coast cities like Seattle and Los Angeles into the sunlight. That’s why sunrise on the East Coast is about three hours earlier than sunrise on the West Coast.

Until the mid-1800s, cities and towns kept their own time. For each of them noon was the exact time when the Sun reached its highest point in the sky. This meant that when the clocks in one town read exactly 12:00, the clocks in a town 50 miles to the east might have read 12:03. As train travel became common, these time differences began to confuse everyone. With each town using its own local time, scheduling arrival and departure times was very complicated. And the train engineers and conductors had to keep resetting their watches to the correct local time. Something had to be done to standardize the time of day.

First, each railroad company used its own standard time for its train schedules. That meant its time didn’t match local times or times for other railroads’ trains. Passengers kept missing their trains, and trains crashed into each other, too. The answer to this problem was time zones.

A time zone is an area of the world where all clocks are set to the same time. The maps in Figure 4 show the time zones for the whole world and a close-up view of the U.S. time zones. Earth is divided into 24 major time zones, because it takes 24 hours for Earth to make a complete rotation around its axis. In 1883, all the railroads divided the United States into four time zones to make a single system of standard time that was known for many years as “railroad time.” When it is noon everywhere in the Eastern Time Zone, it is only 9 a.m. everywhere in the Pacifc Time Zone. It’s even earlier in most of Alaska and Hawaii and midnight in some parts of Asia.

FIGURE 4: TIME ZONE MAPS The map at the top shows time zones of the world. The map below it shows those of the United States.
Now that you have completed the reading, mark whether you agree or disagree with each statement. Under each statement, explain how the activity gave evidence to support or change your ideas.
26.

Ancient people used the shadows cast by sticks to indicate the passage of time during the day.

27.

Evidence from the reading that gives evidence to supprt of change your ideas.


28.

When the sun rises in the western United States, it is still dark in the eastern United States.

29.

Evidence from the reading that gives evidence to supprt of change your ideas.


30.

Benjamin Franklin divided the world into time zones in the late 1700’s.

31.

Evidence from the reading that gives evidence to supprt of change your ideas.


32.

The World is divided into 12 time zones.

33.

Evidence from the reading that gives evidence to supprt of change your ideas.


34.

When it is nighttime in the United States, it is daytime in Asia.

35.

Evidence from the reading that gives evidence to supprt of change your ideas.


36.

What are the properties of the rotation of the Earth?


37.

What effect does the rotation of Earth have on the way people measure time?


38.

How have the your ideas about the cause of Earth’s day-night cycle changed since you began this unit? Create a model that explains what you know. You can draw and write. Note your new understandings.