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( Comet Machholz 2, Jim Scotti 9/9/94)

THE COMET CONNECTION

By Barbara Sprungman

An ideal way to introduce students to comets is to provide them with a "hands-on" astronomical experience.

COMETS

Thanks to the culinary genius of Dennis Schatz, Associate Director and Director of Education for Seattle's famous Pacific Science Center, you can actually create your own comet! Dennis has generously allowed this home page to reprint his successful comet recipe.

Dr. Robert Chapman and Dr. Lynn Bondurant describe the composition of a comet in their publication Comet Halley Returns (listed under Resources) as follows: "In the early 1950's, Dr. F. L. Whipple of the Harvard College Observatory presented a picture of comets that, with some minor modifications, is accepted today. Whipple proposed that the nucleus of a comet is in effect a dirty iceberg, a large mass of frozen water, methane, ammonia, carbon dioxide, and other constituents, in which is embedded meteor-like solid particles of various sizes."

The "Making a Comet in the Classroom" recipe produces a model of this unusually cratered object that definitely looks like it came from outer space. Be sure to take safety precautions when holding the comet -- this is really a "gloves-on" rather than a "hands-on" activity.

Barbara Sprungman, a credentialed teacher and space science education writer, is an associate of Space Data Resources & Information in Washington, D.C.

RESOURCES

Books

For younger students, Comets, Asteroids, and Meteors, a New True Book from Childrens Press of Chicago by Dennis B. Fradin sells for $3.95.

Did Comets Kill the Dinosaurs? is a Dell Yearling Nonfiction book from Isaac Asimov's Library of the Universe series published in 1988 that sells for $4.95.

For students 9-14 years old, The Return of the Comet by Dennis Schatz is a teacher/parent guide that sells for $5 including shipping and handling from the Pacific Science Center Gift Shop, 200 2nd Avenue North, Seattle, WA 98109, or call (206) 443-2870.

The Comet Book by Robert D. Chapman and John C. Brandt is a popular book for older elementary students through adults that was published by Jones and Bartlett Publishers of Boston in 1984.

Comet Halley Returns: A Teachers' Guide, by Dr. R. Lynn Bondurant, Jr. and Dr. Robert D. Chapman, was published for the return of Halley's Comet in 1985-86, but contains a wealth of information on important concepts about comets, including their historical significance, as well as a number of activities for the classroom. Public libraries and NASA Teacher Resources Centers will likely have copies that can be duplicated of this NASA publication.

Posters

The Comets Poster explores both the science and mythology of comets, and is also $9.95. Both are available from the Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, CA 94112, or call (415) 337-2624.

MAKING A COMET IN THE CLASSROOM

By Dennis Schatz
Pacific Science Center, Seattle, Washington

Copyright 1985 by Dennis Schatz

A dramatic and effective way to begin a unit on comets is to make your own comet right in front of the class. The ingredients for a comet are not difficult to find and watching a comet being "constructed" is something the students will remember for a long time.

The "ingredients" for a six-inch comet are:

Other materials you should have on hand include: Dry ice is available from ice companies in most cities (look under "ice" in the Yellow Pages for a local source). Day-old dry ice works best, so you might want to buy it the afternoon before you do the activity. Keep the dry ice in an ice chest when transporting it and in your refrigerator's freezer compartment overnight. Most ice companies have a minimum on the amount of ice they will sell (usually 5 pounds). But having extra dry ice on hand will be useful because some will evaporate and also because it is advisable to practice this activity at least once before doing it with the class.

Here are the steps for making a 6-inch comet (students make good baker's assistants for this exercise!):

  1. Cut open one garbage bag and use it to line your mixing bowl.
  2. Have all ingredients and utensils arranged in front of you.
  3. Place water in mixing bowl.
  4. Add sand or dirt, stirring well.
  5. Add dash of ammonia
  6. Add dash of organic material (e.g. corn syrup), stirring until well mixed.
  7. Place dry ice in 3 garbage bags that have been placed inside each other. Be sure to wear gloves while handling dry ice to keep from being burned.
  8. Crush dry ice by pounding it with hammer.
  9. Add the dry ice to the rest of the ingredients in the mixing bowl while stirring vigorously.
  10. Continue stirring until mixture is almost totally frozen.
  11. Lift the comet out of the bowl using the plastic liner and shape it as you would a snowball.
  12. Unwrap the comet as soon as it is frozen sufficiently to hold its shape.
Now you can place the comet on display for the students to watch during the day as it begins to melt and sublimate (turn directly from a solid to a gas - which is what carbon dioxide does at room temperature and comets to under the conditions of interplanetary space when they are heated by the Sun).

The comet is reasonably safe to touch without getting burned by the dry ice, but it is still best to have a spoon or a stick for the students to use while examining it. As the comet begins to melt, the class may notice small jets of gas coming from it. These are locations where the gaseous carbon dioxide is escaping through 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 disintegrate. 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.