Introduction: (Initial Observation)
Although we see them every day or night, we still don’t have a clear idea of their sizes, distances, speeds, orbits and more important, their effect on our lives. Making a possibly scale model of Sun, Earth and Moon can help us to have a better understanding of their sizes and distances.
Can you use a long ladder to get to the moon? Why lunar and solar eclipse happen?
Information Gathering:
Find out about the Earth, Moon and the Sun. Read books, magazines or ask professionals who might know in order to learn about the sizes and distances of the moon, the sun and the earth. Keep track of where you got your information from.
The Sun happens to be 400 times the Moon’s diameter, and 400 times as far away. That coincidence means the Sun and Moon appear to be the same size when viewed from Earth. A total solar eclipse, in which the Moon is between the Earth and Sun, blocks the bright light from the Sun’s photosphere, allowing us to see the faint glow from the corona, the Sun’s outer atmosphere.
When the Moon is at apogee, it is 11% farther from Earth than it is at perigee. This is far enough that it cannot entirely block the bright light, so eclipses which occur near apogee are not total.
| Earth | Moon | Sun | |
| Mean diameter | 12,742 km | 3,476 km | 1,400,000 km |
| Distance from earth | 0 | 385,000 km | 150,000,000 km |
When Earth, Sun and Moon are in a line, a solar or lunar eclipse will occur. If the Moon is in-between the Earth and the Sun, it blocks the view of the Sun from some parts of the Earth, and this produces a solar eclipse. If, on the contrary, it is the Earth that is in-between the Sun and Moon, then the earth will block the light from the Sun before it can get to the Moon. Since moonlight is just the light the Moon reflects from the Sun, this will darken the Moon, and we get a lunar eclipse.
Since the Moon goes around the Earth every 28 days, shouldn’t we expect a solar eclipse about every 28 days (when the Moon is new), and a lunar one in the same period, (when the Moon is full) ?
Well, this would be so if the orbit of the Moon were in the same plane as the orbit of the Earth around the Sun. But we know eclipses are rarer than that; and the Moon’s orbit is not in the same plane. Instead, it is tilted with respect to it, and the Moon does not in general pass directly on the Earth-Sun line. Moreover, the Moon’s orbit tilt varies slowly. To have an eclipse, then, it is not enough that the three bodies be in the right order; the Moon’s orbit should also be at the right tilt.
About shadows
Whether it is the Moon between the Earth and Sun, or the other way around, the phenomenon is basically the same: the body in the middle casts a cone of shadow, and if the outer body happens to move into this cone, we have an eclipse. It is important to notice that the shadow is more complicated than just a cone: it actually consists of a darker cone, or umbra, where no sunlight reaches, and a lighter region, the penumbra, where only some of the sunlight is blocked. Whether you will be able to observe a total or partial eclipse will depend on which of the two regions you are located in.
Solar Eclipses
A solar eclipse occurs, when the Moon is directly between the Earth and the Sun. As noted above, these are not as frequent as one might expect, but there are still at least two each year. The Moon and the Sun appear to have the same size when viewed from the Earth. The Moon is about 400 times smaller than the Sun, but at the same time the Sun is about 400 times farther away from the Earth than the Moon. Because of this, when there is a solar eclipse, the Moon is about the right size to completely cover the disk of the Sun. If the Moon is close enough to the Earth, it will cover it completely, and we get a total solar eclipse. This is the most spectacular kind, where the day changes into darkness, and one can see the stars in plain day. If the Moon is further away from the Earth, then its disk will not be big enough to cover the Sun completely, and we get an annular eclipse, where most of the sun is covered, but an annulus remains, surrounding the dark disk of the Moon.
Total eclipse
Annular eclipse (ring shape)
In a solar eclipse, the dark part of the Moon’s shadow on the surface of the Earth is a circle of only about 160 miles in diameter. As the Earth moves, this circle traces a path on its surface, called the path of totality. To see a total solar eclipse you have to be inside this rather small region. It is estimated that, on the average, a given spot on the Earth will be on the path of an eclipse only about once every 370 years, so if you like to see an eclipse, it is better to move to an eclipse than to wait for one to come to you.
Lunar Eclipses
As explained above, lunar eclipses do not occur every month because of the inclination of the Moon’s orbit. They do happen at least twice a year, though. And you are far more likely to be able to observe one than a solar one. The reason is that when the Moon gets dark, it is because it does not receive the sunlight, and it then is dark for anyone who can see it. So, instead of having to be in a rather narrow path, as happens for solar eclipses, you only have to be in a part of the world from which the Moon is visible at the time of the eclipse. Pretty much half the world qualifies!
As with solar eclipses, there are partial and total lunar eclipses. If the Moon does not enter into the umbra, the darkest part of the Earth’s shadow, then it does not darken completely, and we get a partial eclipse. These are hard to notice; the Moon just darkens a bit, but does not disappear completely into the night.
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.
The purpose of this project is making models of the sun, Earth and moon in order to demonstrate the proportional sizes and distances or to show their movements in their orbits. Use this model to explain solar or lunar eclipses.
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.
Not required for a display project.
Hypothesis:
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.
Not required for a display project.
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:
Locate the moon in the daytime sky. If it is the first quarter of the month, you can see the moon in the east in the afternoon. If it is the third quarter of the month, you can see the moon in the west in mornings.
Hold a ball in the sunlight, next to the moon so you can see both moon and the ball at the same time.
Observe and compare the shadow and sunlight on the ball and on the moon.
Can you use this experiment to explain why doesn’t the moon look round?
What fraction of the moon is usually exposed to sunlight?
Experiment 2:
Make a model of sun, earth and moon to show that sun is an stationary object, earth rotates around the sun and moon rotates around the earth. Use this model to explain or demonstrate solar and lunar eclipse.
Procedure:
Paint a large Styrofoam ball with yellow color as the sun. Secure the sun on a base board using one or two wood dowels with sharpen end that enters the foam. The other end of the wood dowel may be glued to the base board or inserted in a hole in the board.
Get a straight steel wire about 16″ long and bend it as shown in the above picture. Insert one end of that in the top center of the sun and insert the other end of that in the earth. By now earth should be able to revolve around the sun.
Get a smaller steel wire about 6″ and bend it the same way. Insert one end of this wire in the top center of the earth and the other end into the moon.
By now, moon should also be able to revolve around the earth. This model can be used to demonstrate the Sun, Earth, Moon and their movements. You can also use it to explain occurrence of lunar eclipse and solar eclipse.
The only problem with this model is that the diameter and distances of balls are not proportional to the real diameters and distances. Next activity can demonstrate the true meaning of space and relative distances of sun, earth and moon.
Experiment 3:
Make a scale model of the sun, Earth and the moon to demonstrate their proportional diameters and distances. Use the following table for sizes.
| Sun | Earth | Moon | |
| Real Diameters | 1,400,000 km | 12,742 km | 3,476 km |
| Proportional diameters in your scale model | 70 cm (2.5 feet) |
6.5 mm (1/4 inches) |
1.5 mm (1/16 inches) |
Procedure:
- Get a very small white glass or plastic bead to be the moon. This must be the size of a small circle like this º. The diameter of the moon in your model must be about 1.5 millimeters.
- Get a larger plastic or glass bead to be the Earth. This will be the size of a chick pea or about 6 to 7 mm in diameter.
- Get the largest orange or yellow balloon that you can find to be the sun in your model. It should be about 70 cm in diameter (2.5 feet).
- Get a string and pass it trough the earth and moon beads. Use knots to hold the beards on the string about 18 cm (1.5 feet) apart. This is the distance between the earth and the moon in your model.
- Use another string about 75 meters long (250 feet) to connect the earth to the sun. This is the distance between the earth and the sun in your model. Wind this long string around a cardboard until you go into a large space for your final observation.
- In a park or in another large space, ask your friend to hold the balloon. Hold the earth and moon in your hand and distance from your friend while unwinding the string that connects the earth to the sun. When there is no string left, you should be about 75 meters (250 feet) away from your friend.
- Keep the earth in your left hand and the moon in your right hand and stretch the string connecting these two. Make your final observation to have a good idea about the relative sizes and distances of the sun, Earth and the moon.
Additional experiments:
While the sun is 250 feet away from you, close your left eye and hold the moon between your eyes and the sun. Move it back and fourth until it covers the sun. How far is the moon from your eyes when it can fully cover the sun? Compare this distance with the distance from earth to the moon.
Materials and Equipment:
List of material can be extracted from the experiment section.
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.
Calculations:
To find the acceptable sizes for this model, we are dividing the real numbers by 2,000,000,000 that is a large number. To make it simpler to understand, we use one millimeter to show 2000 km.
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.
Write what you have learned from this project in your own words.
Conclusion:
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.
