Introduction: (Initial Observation)
In summer, the days are long and the weather is warm. In winter the days are short and the weather is cold. Why is there a difference between the summer and winter? Why do we have less daylight and long nights in winter?
Earth is always spinning with the same speed. It takes 24 hours for the earth to rotate once, regardless of the season. So why is there a difference in the day length in summer and in winter?
The reason that I want to learn about day length is that I think day length is affecting many aspects of our lives. First the weather changes. When days are short, we get less heat from the sun and the air temperature drops.
In short winter days no plants can grow and agricultural businesses are in halt. In winter we consume more energy for heat and lighting and in general winters are very costly.
Find out about what the earth and it’s rotation speed. Read books, magazines or ask professionals who might know in order to learn about the solar system and the orbit of the earth around the sun. Keep track of where you got your information from.
If you search the Internet to gather information, you may search for keywords such as Day Length, Solar System, Earth Seasons. Following links show samples of information that you might find.
You may need or be required to gather some information from books as well. Visit your local library and look for a book about solar system or search the sections with astronomy or geography books.
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.
The purpose of this project is to understand and demonstrate the cause of changes in day length from winter to summer.
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.
Since the speed of earth rotation is constant, the only other variable that may affect the day length in different days of the year is the tilt in earth rotation axis. This angle is an independent variable.
Day length is the dependent variable.
In other words we are saying that the day length is possibly affected by the tilted earth axis and we are going to test it.
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. Following is a sample hypothesis:
My hypothesis is that when the earth north pole is tilted toward the sun, a larger portion of the earth latitude lines in north hemisphere will be in the light area. That makes the days longer. The same happens for the south hemisphere when the south pole is tilted toward the sun.
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.”
Gathered information indicates that a 23.5º tilt in the earth rotational axis with respect to the plane of earth orbit is causing the difference in day length in different days of the year. As a result, when the Earth is at a certain place in its orbit, the northern hemisphere is tilted toward the Sun and experiences summer. Six months later, when the Earth is on the opposite side of the Sun, the northern hemisphere is tilted away from the Sun and experiences winter. The seasons are, of course, reversed for the southern hemisphere. So we design and make a model of earth with tilted axis and use it to observe the day length in different days or seasons of the year.
Get a piece of cardboard about 24″ x 24″ and install a light bulb in the center of that to represent the sun.
Draw a circle with the radius of about 10″ around the light bulb.
Divide the circle into 4 equal parts and insert four equidistance toothpicks in the circles perimeter in a way that all toothpicks are tilted to one direction about 23.5º.
Get some Styrofoam balls and paint them as earth models. Make sure to mark south and north poles and show some latitude lines. Try to draw the equator and 2 latitude lines (40º South and 40º North). You may paint them using a brush or insert them partially in a water based paint solution. Painting in this way requires a lot of hours waiting for each paint to dry before you can try the other one.
Place a Styrofoam ball over each toothpick such that the tooth pick passes the center of each ball and act as the earth rotation axis.
Turn on the light and mark the area of each latitude line that is illuminated by the light.
Light will represent the sun and each ball represents the earth in a different position of it’s orbit. Compare the illuminated section of each latitude line with dark section of the same latitude line for all four positions of earth around the sun.
Do this in a dark room. It will be easier to identify the areas that are dark. It will also be easier to see what portion of each latitude line in in the dark. Make a close observation and mark the seasons based on northern hemisphere.
In this experiment you will use a globe as your earth model and use a flashlight or a desk lamp as the sun to see how does the tilt in the earth axis affect the daylight hours. Also try to calculate the number of daylight hours in summer.
When I got my globe, I noticed that it’s rotation axis is already tilted 23.5º and it is ready to use. Most likely yours will be tilted too.
Turn on the light on the desk and make it faced to the globe and at the same level or elevation. Turn the globe base in a way that the north pole be tilted toward the light.
Do you have more light on north hemisphere or south hemisphere?
Make a look from the top (or from north pole). See one of the latitude lines. What portion of latitude line is in the dark? Carefully mark the points in a latitude line where the light ends.
Use a meter stick or a ruler to measure the length of the specific latitude line which is in the light. Also measure the length of the dark portion of the same line. Use these to calculate the longest day length. The circle is drawn on latitude 55ºN.
Now turn the base of the globe in a way that the north pole be tilted away from the sun. Compare the light in northern hemisphere with the light in the southern hemisphere.
Compare the light in the north pole with the light in the south pole. What day of the year is this in the northern hemisphere? Is it winter or summer?
When the north pole is tilted away from the sun, look at the globe from the north pole direction. You can see the portion of the light in the northern hemisphere.
Make drawings or pictures from your experiment setup and experiment results and use them as a part of your display.
Is there any change in day light hours in equator in different seasons?
Materials and Equipment:
This list of material can be modified based on your final design.
- Foam board or strong cardboard or wooden board about 2′ x 2′
- 4 Plastic or Styrofoam balls (Also get a few extra balls for practice)
- Steel Wires or wooden barbeque sticks
- Water base paints
- Pencils and markers
- Light bulb and base or socket
- some wires and battery
- Desk lamp or flashlight
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.
Make close observation to the model that you have made and try to answer your questions.
When the north pole is tilted away from the sun, north pole is in the darkness. No matter how we rotate our earth model around it’s axis, north pole remains in the dark. Don’t you think that north pole night takes 6 months?
This is the part of year that the northern hemisphere gets less sunlight.
This image shows the north pole image when the north pole is tilted away from the sun. As you see the north pole which is in the center of the image is quite dark.
Do the people in the north pole ever see the sun over their head?
When the north pole is tilted toward the sun, northern hemisphere gets more light. This model shows me that north pole will never get a large amount of sunlight.
What happens in the south pole when we have sunlight in the north pole?
You may want to calculate the number of daylight hours in the summer using the experiment number 2. This is a sample calculation.
I want to calculate the day length for 55ºN in the longest day of summer. I positioned the north pole away from the sun (desk lamp) and took a picture from the direction of north pole. Then I marked the light area with red marker and dark area with yellow marker. The length of the dark area line was 13.5 cm (Centimeter), the length of the light area line was 21 cm. (Obviously the total will be 34.5 cm)
To calculate the daylight I divided 21 by 34.5 and multiplied the result by 24 (because each rotation of earth takes 24 hours)
Day light in 55ºN in the longest day of summer = 21/34.5 x 24 = 14.6 hours.
I compared this result with other data on the Internet and noticed that the actual number of daylight hours must be about 17 hours. So my results are not accurate.
See Possible Errors section.
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.
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.
Although my results and analysis of daylight in different parts of the earth matches the actual data, my calculation of daylight is off the track!
The fact that I did not do my experiment in a fully dark room, may have caused some error. In other words I ignored parts of the light from the desk lamp because they were not visible to me. If I would do the experiment in a dark room with black walls (to avoid light reflections), the results could be different.