Sky Science

Students will be able to:

1. Support an explanation for the colors we see in Earth's sky with evidence from a model
2. Critique a scientific model, including identifying its limitations
3. Explain why we see different colors in Earth's sky at different times of day.

1. Set up Sky Science slides.
   
2. Print one set of notebook pages for each student.
   
3. Prep set of lab materials for each group of 3-4 students.
   
4. Arrange all "further investigation" materials in a separate location, to reveal later.
   
5. Block out windows or other light sources if necessary.
   
6. You may want to try the investigation yourself ahead of time to make sure that the room gets dark enough to see the effect of adding milk to the colors you observe.

Student Notebook Teacher Tip: The student pages for this activity were created to be part of a notebook wherein student thinking and work is collected, and designed to leave room for students to flexibly use the space around the prompts, diagrams, etc. These pages could be glued into students' science notebooks in their entirety, or could be edited to make smaller data tables, prompts, and diagrams for students to glue in as they move through the lesson.

1. Put students into groups of 2-4.
   
2. Hand out notebook page 2. Ask each student to write it down the focus question in the space provided.
   
3. Using Slide 3, introduce the materials and steps of the initial investigation. You may want to demo shining the light through the water in different directions, and observing from below and above, as well as from the side and the end facing the light source.
   
4. Give each group the materials for Investigation Part 1 (see Materials)
   
5. Check in with each group briefly to make sure they have decided on roles and understand the task.
   
6. Once groups are ready, turn off the lights and give groups 3-5 minutes to observe plain water only. (Note: if you are projecting the powerpoint slides, remember to turn off the projector to make the room fully dark)
   
7. Once all groups have observed plain water, all groups should add skim milk to the water and stir. Give groups at least 5 minutes to observe with the lights off once they have completed this step.
   
8. Encourage students to take notes in their notebooks about what they observe, using words and sketches to show what colors they saw in the bucket and where.
   
9. Turn the lights on. Give students 3-5 minutes to finish up their notes and sketches now that they have more light.

Teacher Tip: Group work roles for investigation. It could be useful to have group members to choose roles, including: 1) Materials Manager to get and set-up materials; 2) Notetaker to make sure predictions and observations are recorded in at least one notebook; and a 3) Facilitator to read directions and manage the process. These can be rotating roles if students want to try something new in Part 3, below.

1. Hand out notebook page 4.
2. Tell students that their next task is to plan a new investigation in order to test their explanation:
   • Groups should decide on one thing to change in their model in order to test their explanation.
   • Possible things to change include:
     • Shape of the container
     • The type of milk in the water
     • The amount of milk in the water
     • The color of the light
   • Reveal the optional materials to students, so they know what materials they have available as they plan their investigation.
   • In addition to recording their plan in words and/or pictures, groups should be sure to make a prediction: Based on their current explanation, what effect do they predict this change to the model will have on what they observe?
     
3. Give groups about 10 minutes to plan, circulating to be sure everyone is recording plans and predictions in their notebooks.
   
4. Once all groups have planned, made a prediction, and set up their new model, turn off the lights to test!
   
5. Visit each group and ask open-ended questions about their test:
   • What change did you make to your model and why?
   • What do you notice?
   • Are your observations agreeing with your prediction?
   • What are you thinking now? What do you wonder?
     
6. Some groups may move faster, so you may open it up to them to make another change to their models.
   
7. When everyone has tested and discussed at least one change, turn the lights on.
   
8. Give groups 3-5 minutes again with the lights on to record their observations and new thoughts and ask them to discuss with their group:
   • Based on what you observed, do you need to revise your explanation?
   • What are you wondering now?
   • What would you want to try next.
     
9. Give these sentence frames to help them shape their thinking in their notebooks:
   • "Now, we think_________ because__________."
   • "We confirmed our thinking because_________."
   • "Now, I wonder...

1. Remind students of the image on their first notebook page.
   
2. Ask students to think individually about these questions before sharing with an elbow partner:
   • Which bucket (milky or plain water) is more like Earth's sky? Milky.
   • Which bucket is more like the moon's sky? Plain.
   • Why do you think that? Some possible answers: Earth has an atmosphere. Light interacts with the particles in the milky water, as it does with Earth's atmosphere, so you can see the light passing through the milky water and lighting up the bucket, as the sun lights up the sky. In the plain water, the light passes through the water without interacting with many particles. Similarly, the moon's sky stays dark because it doesn't have a thick atmosphere like Earth. You can see the sun in the distance, and you notice it when it hits the flag or the astronaut, kind of like when it hits the side of the bucket or your hand.
     
3. Ask for volunteers to share out their thoughts. Students will be ready to move on when most people agree that the milky bucket is more like Earth's sky.
   
4. Hand out page 5.
   
5. Ask students to think individually about these questions before sharing with an elbow partner. You may want to remind them of the focus question, which should be written in their notebook: Why do we see the colors we do in Earth's sky?
   • What do you think this diagram is intended to show?
   • How does it relate to the focus question?
   • How does it relate to our model?
     
6. Ask for volunteers to share out their thoughts. Key ideas here are that the diagram is showing that different colors of light are scattered differently by Earth's atmosphere. The diagram seems to be saying that blue and violet light are scattered more easily. Students may notice that this parallels their observation of the model, where the light passing all the way through the water was yellow, or orange. Students also might notice that in our model, the milky water takes the place of (or "represents") Earth's atmosphere, and light coming from the flashlight represents the sun's rays in space.
   
7. Hand out page 6.
   
8. Ask students to think individually about these questions before sharing with an elbow partner.
   • What do you think this diagram is intended to show?
   • How does it relate to the focus question?
   • How does it relate to our model?
     
9. Ask for volunteers to share out their thoughts. One key idea, again, is that the diagram is showing that different colors of light are scattered differently by Earth's atmosphere. The diagram shows in a different way that blue and violet light are scattered more easily. It also includes in this representation the idea that the distance light passes through the atmosphere to reach us depends on our position on the Earth relative to the Sun, which changes as Earth rotates. When the sun has a direct path, the blue light is scattered by the atmosphere making the sky look blue, and we often think of the sun as looking yellow. As Earth rotates away from the sun, what we think of as the sun "setting," the sunlight passes through more atmosphere, scattering more colors, including the reds, oranges, and yellows that we often see in the evening - and for the same reason in the morning as the sun is rising.

This activity is anchored in the phenomenon of the colors we see in Earth's sky. The phenomenon is introduced through a selection of images that contrast the colors we see in Earth's sky (at noon on a cloudless day, or at sunset) with images from the moon where the sun or sunlight is visible, but the sky remains black. The observations and questions that come out of this introduction help students connect to the focus question which guides the investigation: "Why do we see the colors we do in Earth's sky?"

Investigating and critiquing a model

The goal of this activity is to build towards an answer to the above question by investigating and critiquing a physical model of the phenomenon that leads to the colors in Earth's sky. Students have the opportunity to work with the model in three different ways. First, they follow step-by-step directions to create the basic model, adding skim milk to water and observing what happens to light as it passes through the milky water. This is the point where students are given some key ideas and vocabulary for talking about light and its interactions (transmit, reflect, refraction, and scatter), and asked to discuss and write a team explanation for what is happening to the light in the "bucket." Based on this explanation, they are given a second opportunity to investigate this model by changing one thing that they think will test their explanation. Finally, students engage in critique of the model by comparing it to scientific diagrams, and identifying the limitations and strengths of the bucket model in representing the real phenomenon.

What can you expect to see in the bucket?

When you shine the flashlight through the water in the bucket, there are very few particles large enough for the light to interact with. Most of the light passes through without being reflected, absorbed, or scattered, traveling in a straight line from its source. Looking down on the water or in from the side you don't see very much light and the bucket still looks dark. However, you can see the light when you look through the bucket towards the light source, shining brightly from the other side of the bucket.

After skim milk has been added, light is scattered by the larger particles that have been introduced to the water. Now when you look down into the bucket, more of this randomly scattered light reaches your eye, and instead of a dark bucket, you see a bucket filled with light. Much of the light looks white, but as you observe more closely, you may notice that different colors are more visible in locations closer to or further from the light source.

How does this model the sky?

One phenomenon that the model helps us understand is that the sky viewed from the moon is dark, with a bright sun visible like a spotlight, while the sky viewed from Earth is filled with color. This model helps us consider how the Earth's atmosphere causes a phenomenon we may take for granted.

Augustine, J. & Smith, L. (n.d.). Red sky in morning, sailor take warning. Red sky at night, sailor's delight. National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory, Global Monitoring Division. Retrieved from: http://www.esrl.noaa.gov/gmd/grad/about/redsky/

Blue Sky from Exploratorium Science Snacks. Retrieved from: http://www.exploratorium.edu/snacks/blue-sky

Light waves and color (n.d.) on The Physics Classroom. Retrieved from: http://www.physicsclassroom.com/class/light/Lesson-2/Light-Absorption,-Reflection,-and-Transmission

Rayleigh scattering (n.d.) on Hyperphysics. Retrieved from: http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c2

Image: "Mammatus clouds and crepuscular rays" by Brocken Inaglory, licensed and modified under CC BY-SA 3.0; originally sourced from https://commons.wikimedia.org/wiki/File:Mammatus_clouds_and_crepuscular_rays.JPG