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    Make a Comet
    By Lori 2

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    We make comets in our classroom in two ways -- I got these ideas from a NASA website. I do these after reading Maria's Comet by Deborah Hopkinson. I also have the class listen to the song Halley Came to Jackson by Mary Chapin Carpenter.

    Dry Ice Comet Demo

    Materials:

    2 cups water

    2 cups dry ice (frozen carbon dioxide) Caution
    dry ice is -79 degrees celsius or -110 degrees Farenheit. Any more than the briefest exposure to skin will cause "burns." Everyone handling dry ice should wear heavy rubber gloves! Be sure to discuss safety precautions with students when working with dry ice. Day old dry ice works best for this experiment. Keep the dry ice in an ice chest when transporting and in your freezer overnight. Many ice companies have a minimum on the amount of ice they will sell (usually 5 pounds). Having extra dry ice on hand is useful, however, because some will evaporate and also because it is advisable to practice this activity at least once before doing it with a class.

    2 tablespoons of sand or dirt

    dash of ammonia

    dash of dark corn syrup

    ice chest

    newspapers

    four medium sized garbage bags

    heavy duty rubber gloves

    hammer, meat mallet, or rubber mallet

    large mixing bowl

    large wooden spoon

    paper towels

    hair dryer (optional -- use with caution)


    Procedure:

    Cut open a garbage bag and use it to line the mixing bowl.

    Have all ingredients and utensils arranged in fron of you before you beginn.

    Pour water into the mixing bowl.

    Add sand or dirt, stirring well.

    Add a dash of ammonia.

    Add a dash of corn syrup, stirring until well mixed.

    Place the dry ice into three garbage bags that have been place inside each other. Be sure to wear the heavy rubber gloves while handling the dry ice to keep from being burned.

    Crush the dry ice by pounding it with a hammer. This is very easy to do.

    Add the dry ice to the rest of the ingredients in the bowl while stirring vigorously.

    Continue stirring until the mixture is almost frozen.

    Lift the comet out of the bowl using the plastic liner and shape it as you would a snowball.

    Lift the comet out of the bowl using the plastic liner and shape it as you would a snowball.

    Unwrap the comet as soon as it is frozen sufficiently to hold its shape. Now you can place the comet on display for the rest of the day as it begins to melt and sublimate (turn directly from a solid to a gas -- which is what frozen carbon dioxide does at room temperature and comets do under the conditions of interplanetary space when they are heated by the sun's rays).

    Explanations and Observations:

    Students should only examine the comet with a wooden spoon and with heavy duty rubber gloves. As the comet begins to melt, the class may notice small jets of gas coming from it. THese are the locations where gaseous carbon dioxide is escaping through the small holes in the still frozen water. This type of activity is also detected on real comets, where the jets can sometimes expel sufficient quantities of gas to make small changes in the orbit of the comet.

    After several hours, the comet will become a crater-filled ice ball as the more volatile carbon dioxide sublimates before the water ice melts. Real comets are also depleted by sublimation each time they come near the sun. Ultimately, old comets may break into several pieces or even completely disintergrate. In some cases, the comet may have a solid, rocky core that is then left to travel around the comet's orbit as a dark barren asteroid.

    The ingredients used to build the comet represent our current understanding of the components found in actual comets; frozen water, frozen carbon dioxide and other frozen gases, dust and rock, and organic or carbon-based substances -- represented by the corn syrup.

    Scientists have studied the spectrum of light coming from real comet's comas and tails to determine the presence of these materieal.

    I have some observation questions for this experiment/demo but would probably be more appropriate for older students.



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