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Sky Color- account for differences in color at different times

Sky Color- account for differences in color at different times

Introduction: (Initial Observation)

The sky color is blue most of the day when it is clear, but it turns yellow and red at sunset until it disappears. As the sun rises again, the sky color is red and yellow and soon it becomes blue again. In this project we will investigate the reasons for these changes.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Following is a list of resources for this project:

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

Whenever it’s not completely filled with clouds, we can see that the sky is blue. As the sun rises and as it sets, it looks red. Are these two observations related? Can the sky color be related to the angle of sun light and the earth’s atmosphere?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

The independent variable is the angle of the sunlight.

The dependent variable is the color of the light that arrived to us after refraction by the atmosphere.

Controlled variables are temperature, moisture, time of the year.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. This is a sample hypothesis:

I hypothesize that the earth’s atmosphere is refracting the sunlight in a way that red color (the lowest color) remains in the atmosphere and all other colors exit toward the sky. My hypothesis is based on my observation of prisms that refract the light and produce a rainbow of different colors.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:


This experiment is intended to show how light is affected when passing trough different media. You will need the following materials:

  1. a flashlight
  2. a transparent container with flat parallel sides (a 10-liter [2½-gallon] aquarium is ideal)
  3. 250 milliliters (1 cup) of milk


Set the container on a table where you can view it from all sides. Fill it ¾ full with water. Light the flashlight and hold it against the side of the container so its beam shines through the water. Try to see the beam as it shines through the water. You may be able to see some particles of dust floating in the water; they appear white. However, it is rather difficult to see exactly where the beam passes through the water.

Add about 60 milliliters (¼ cup) of milk to the water and stir it. Hold the flashlight to the side of the container, as before. Notice that the beam of light is now easily visible as it passes through the water. Look at the beam both from the side and from the end, where the beam shines out of the container. From the side, the beam appears slightly blue, and on the end, it appears somewhat yellow.

Add another ¼ cup of milk to the water and stir it. Now the beam of light looks even more blue from the side and more yellow, perhaps even orange, from the end.

Add the rest of the milk to the water and stir the mixture. Now the beam looks even more blue, and from the end, it looks quite orange. Furthermore, the beam seems to spread more now than it did before; it is not quite as narrow.

What causes the beam of light from the flashlight to look blue from the side and orange when viewed head on? Light usually travels in straight lines, unless it encounters the edges of some material. When the beam of a flashlight travels through air, we cannot see the beam from the side because the air is uniform and the light from the flashlight travels in a straight line. The same is true when the beam travels through water, as in this experiment. The water is uniform and the beam travels in a straight line. However, if there should be some dust in the air or water, then we can catch a glimpse of the beam where the light is scattered by the edges of the dust particles.

When you added milk to the water, you added many tiny particles to the water. Milk contains many tiny particles of protein and fat suspended in water. These particles scatter the light and make the beam of the flashlight visible from the side. Different colors of light are scattered by different amounts. Blue light is scattered much more than orange or red light. Because we see the scattered light from the side of the beam, and blue light is scattered more, the beam appears blue from the side. Because the orange and red light is scattered less, more orange and red light travels in a straight line from the flashlight. When you look directly into the beam of the flashlight, it looks orange or red.

What does this experiment have to do with blue sky and orange sunsets? The light you see when you look at the sky is sunlight that is scattered by particles of dust in the atmosphere. If there were no scattering, and all of the light traveled straight from the sun to the earth, the sky would look dark as it does at night. The sunlight is scattered by the dust particles in the same way as the light from the flashlight is scattered by particles in milk in this experiment. Looking at the sky is like looking at the flashlight beam from the side: you’re looking at scattered light that is blue. When you look at the setting sun, it’s like looking directly into the beam from the flashlight: you’re seeing the light that isn’t scattered, namely orange and red.

What causes the sun to appear deep orange or even red at sunset or sunrise? At sunset or sunrise, the sunlight we observe has traveled a longer path through the atmosphere than the sunlight we see at noon. Therefore, there is more scattering, and nearly all of the light directly from the sun is red.

Experiment 2:

Introduction: This experiment will show the relation between the color of sky and the angle of the sun. You must do this experiment if you need a results table and a graph for your project guide.


Mount a cardboard or wooden board vertically on another cardboard or wooden board. Insert a nail or needle in the on the cardboard and then place the cardboard in a horizontal sunny space so that you can see the shadow of the needle on the board. You should be able to use a protractor to measure the angle of the shadow which is the same as the angle f the sun rays. This will be your instrument to measure the angle of the sunlight when you need.

In a sunny day with clear sky start to record the angle of the sunlight and the color of the sky. For each color, record the start and the end time. Repeat this for 3 different days. Record your results in a table like this:

Blue/ white Color Yellow Color Orange Color Red Color
Start Angle End Angle Start Angle End Angle Start Angle End Angle Start Angle End Angle
Day 1
Day 2
Day 3

Take the average of the 3 days and write the averages in the last row of your results table. These are also the numbers you use in your graph or chart.

Make a chart or graph:

The best type of graph you may use for this project is a pie graph. The reason is that your results are ranges of angles for different colors. If the angles overlap, place the boarder line in between.

For example if the sky is red while the angle of the sun is between 0 to 5 degrees, then you paint red a pie between the 0 to 5 degrees.

If the sky remains red 13 minutes after the sunset, then you calculate the angle of sun instead of measuring it. The angle of sun changes 15 degrees each hour. So in 13 minutes sun goes down 3.25 degrees. That will be -3.25 degree because it goes downward.

Materials and Equipment:

You will need the following materials:

a flashlight
a transparent container with flat parallel sides (a 10-liter [2½-gallon] aquarium is ideal)
250 milliliters (1 cup) of milk

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.



Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.