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Eclipses
Experiment Central: Understanding Scientific Principles Through Projects. 2nd ed. 2010. Lexile Measure: 1110L.
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Imagine living in ancient times. You stroll down a dirt road leading to a favorite temple. It is a nice day, but without warning, the sky starts to get dark. The Sun looks strange and, gradually, something huge blocks it out, although a bright ring can be seen around its edge.

We now know that this phenomenon is a solar eclipse. An eclipse occurs when one celestial body passes in front of another, partly or completely cutting off our view of it. Today, we would get advance information through newspapers and magazines or by news reports on television or radio if a major eclipse was expected. To most ancient people, who had no explanations for the darkness, an eclipse was terrifying.

Close encounters in the sky

In the eighth century B.C.E., Babylonian scholars began systematically observing and writing down celestial phenonema, as they studied astronomy. These scholars watched the motion of the planets and noticed that sometimes two planets came close together. Sometimes the Moon passed in front of the Sun. Sometimes Earth's shadow fell on the Moon. After studying these phenomena for many years, they identified certain experiences as occurring in cycles. They also developed mathematical formulas involving time and distances that helped them to predict eclipses.

Thales of Miletus (624-546 B.C.E.) was a Greek philosopher who may have learned astronomical methods from the Babylonian scholars. Thales accurately predicted a solar eclipse on May 28, 585 B.C.E.--probably the earliest, most public eclipse prediction. The term eclipse comes from the Greek words meaning "to leave out," because when one occurred, either the Sun or the Moon was "left out." In fact, the theory that Earth was a sphere began getting attention around this time because observers noticed that Earth's shadow on the Moon during eclipses was always circular.

The first eclipse to interest a significant number of astronomers took place on April 22, 1715. The shadow of the eclipse fell across Great Britain and parts of Europe. English astronomer Edmond Halley (1656-1742) plotted its path and prepared maps enabling many to watch its course.

Celestial line-up

The two most commonly known eclipses are solar and lunar. Earth revolves around the Sun. The Moon revolves around Earth. The Moon takes a month to complete a revolution; Earth takes a year. Sometimes these three bodies end up in a straight line and cause an eclipse.

Two conditions have to be met for a total solar eclipse--one in which our view of the Sun is completely blocked. The Sun, Moon, and Earth must lie in a perfectly straight line, and the Moon must be a certain distance from Earth to cover the Sun. When these conditions are met, the Moon totally blocks our view of the Sun for a period of about seven minutes. If the Moon is too far away from Earth, or if it is not exactly aligned between Earth and the Sun, it will only partially block the Sun, causing a partial solar eclipse.

For a total lunar eclipse, the Sun, Earth, and Moon must lie in a perfectly straight line. Did you catch the difference? In this case, Earth is in the middle, not the Moon. Earth's shadow across the Moon is what causes the darkness. Lunar eclipses can happen only during a full Moon, when Earth's dark side faces the Moon's bright side. In this position, Earth casts a shadow, causing the Moon to darken.

Celestial fireworks

The bright ring you might see around the Sun during a solar eclipse is the corona, the Sun's outermost layer, which appears to be a pearly color. The red plumes that shoot out around this ring are called prominences.

Like fireworks, these streams of glowing gas shoot out from the Sun and extend many miles into space. No wonder ancient people were terrified. Lunar eclipses have a colorful side also. They can make the Moon turn red. This reddish color is actually an accumulation of light waves from the Sun.

By constructing models that simulate eclipses, we can better understand the extraordinary processes that cause them.

Words to Know

Astronomy
The study of the physical properties of objects and matter outside Earth's atmosphere.
Celestial bodies
Describing planets or other objects in space.
Corona
The outermost atmospheric layer of the Sun.
Cycles
Occurrence of events that take place on a regular, repeating basis.
Eclipse
A phenomenon in which the light from a celestial body is temporarily cut off by the presence of another.
Gibbous moon
A phase of the Moon when more than half of its surface is lighted.
Hypothesis
An idea in the form of a statement that can be tested by observation and/or experiment.
Lunar eclipse
An eclipse that occurs when Earth passes between the Sun and the Moon, casting a shadow on the Moon.
Partial solar/lunar eclipse
An eclipse in which our view of the Sun/Moon is only partially blocked.
Phases
Changes in the portion of the Moon's surface that is illuminated by light from the Sun as the Moon revolves around Earth.
Prominences
Masses of glowing gas, mainly hydrogen, that rise from the Sun's surface like flames.
Solar eclipse
An eclipse that occurs when the Moon passes between Earth and the Sun, casting a shadow on Earth.
Total solar/lunar eclipse
An eclipse in which our view of the Sun/Moon is totally blocked.
Variable
Something that can affect the results of an experiment.

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PROJECT 1

Simulating Solar and Lunar Eclipses

Purpose/Hypothesis

This project will create a model that demonstrates a solar and lunar eclipse. By adjusting the alignment and distances of the model Sun, Moon, and Earth, you should be able to demonstrate both partial and total eclipses.

Level of Difficulty

Easy/moderate. (The assembly and principles are not difficult, but it takes patience to adjust the objects to get the desired effect.)

Materials Needed

  • 2 Styrofoam balls, one ball 2 inches (5 centimeters) and one 0.5 inch (1.25 centimeters) in diameter
  • two 4-inch (10-centimeter) Styrofoam squares
  • small table lamp (measuring 12 inches in height) with no lamp shade and a 40-watt bulb
  • 2 wooden dowels (as long as the height of the lamp from its base to the middle of the bulb)
  • ruler

Approximate Budget

$3 for the Styrofoam pieces and the dowels.

Timetable

Less than one hour.

How to Experiment Safely

Use caution when handling the lamp. Do not touch or move it until it has cooled for at least five minutes.

Step-by-Step Instructions

  1. Poke each dowel into the center of a Styrofoam square.
  2. Place the small Styrofoam ball, representing the Moon, onto one dowel.
  3. Place the large Styrofoam ball, representing Earth, onto the other dowel.
  4. Place the lamp on a sturdy table and plug it in. Turn it on.
  5. Here is the challenge! Place the Sun (lamp), Earth (large ball), and Moon (small ball) on a flat surface in perfect alignment to create a solar and lunar eclipse. Follow the diagrams illustrated.

Summary of Results

Make a diagram of your experiment, measuring and marking the distances and height of the experiment parts for others to see and try. Through the shadows you created with the lamp, were you able to create full eclipses or only partial eclipses?

Troubleshooter's Guide

Here is a problem that may arise during this project, a possible cause, and a way to remedy the problem.

Problem: You cannot get the shadow to cover the entire object to create the "eclipse."

Possible cause: Your alignment may be off. Make sure you line up the objects on the same level.

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PROJECT 2

Phases of the Moon: What does each phase look like?

Purpose/Hypothesis

In this project, you will create models of the changes in the illuminated Moon surface as the Moon revolves around Earth. These changes are called phases. You will create diagrams called sun prints representing these Moon phases.

Level of Difficulty

Easy/moderate.

Materials Needed

  • 8 sheets of dark blue construction paper, 8½ x 11 inches (21.5 x 28 centimeters)
  • 8 sheets of black construction paper, 8½ x 11 inches (21.5 x 28 centimeters)
  • adhesive tape
  • marker
  • 30 x 30-inch (75 x 75-centimeter) board
  • sunny day
  • scissors
  • drawing compass

Approximate Budget

$5 for paper supplies.

Timetable

Approximately 1 hour to set up the model and a whole day for the sun prints to mature.

How to Experiment Safely

Use caution with the compass and scissors.

Step-by-Step Instructions

  1. Use the compass to draw a 7-inch (18-centimeter) diameter circle on eight sheets of blue construction paper.
  2. Draw an 8-inch (20-centimeter) diameter circle on eight sheets of black construction paper.
  3. Cut out the circles.
  4. Tape eight blue circles onto the board in a circle.
  5. Mark the board as shown in the diagram illustrated above.
  6. Place the black circles over the blue circles to show: new Moon; crescent Moon; first-quarter Moon; gibbous Moon; full Moon; gibbous Moon; third-quarter Moon; crescent Moon.
  7. Leave the board in a sunny location for at least 8 hours.
  8. Take the black paper off after 8 hours and examine the results.
  9. Highlight the lightened areas or boundaries with the marker.

Note: the darker blue areas that were covered are the shaded part of the Moon we cannot see.

Summary of Results

Label the board and write a brief description for each Moon phase, that is, how it was caused and what it looks like.

Troubleshooter's Guide

Here is a problem that may arise during this project, a possible cause, and a way to remedy the problem.

Problem: The sun prints are not forming.

Possible cause: They have not had enough time. Give the sun prints two days, for eight hours each day, in full sunlight.

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Design Your Own Experiment

How to Select a Topic Relating to this Concept

Astronomy is a fascinating field of study, with topics such as meteor/meteorites, telescopes, space travel, and stars. Read your local paper to find out about upcoming events in the sky. Then research who saw the phenomena first and when and how theories developed.

Check the Further Readings section and talk with your science teacher or school or community media specialist to start gathering information on eclipse questions that interest you.

Steps in the Scientific Method

To do an original experiment, you need to plan carefully and think things through. Otherwise, you might not be sure what question you are answering, what you are or should be measuring, or what your findings prove or disprove.

Here are the steps in designing an experiment:

  • State the purpose of--and the underlying question behind--the experiment you propose to do.
  • Recognize the variables involved, and select one that will help you answer the question at hand.
  • State a testable hypothesis, an educated guess about the answer to your question.
  • Decide how to change the variable you selected.
  • Decide how to measure your results.

Recording Data and Summarizing the Results

When performing an experiment, it is important to keep your data organized in tables. Your information needs to be analyzed and presented in a visual manner. Graphs, drawings, or pictures of events are great tools for displaying your data.

Related Projects

Creating models like these are always fun and interesting. However, creating a mini-instrument, such as a telescope with lenses and cardboard, might be useful. Ask a teacher or your parents for help.

Source Citation   (MLA 8th Edition)
Nelson, M. Rae. "Eclipses." Experiment Central: Understanding Scientific Principles Through Projects, edited by Kristine Krapp, 2nd ed., UXL, 2010. Science In Context, http%3A%2F%2Flink.galegroup.com%2Fapps%2Fdoc%2FCV2644200012%2FSCIC%3Fu%3Dgale%26sid%3DSCIC%26xid%3Deb036129. Accessed 17 Feb. 2019.

Gale Document Number: GALE|CV2644200012