Learning about astronomy is a great way to spark a child’s imagination and engage them in the world of science! In this activity, we’ll learn all about comets.
The visible parts of a comet are the coma, dust tail and ion tail. However the heart of the comet is the nucleus. It’s actually fairly small, maybe the size of a few blocks up to the size of a small village (about 1/2 – 10 miles). Like most small objects is space, the nucleus is covered in craters.
The nucleus contains silicates (rock and sand), carbon, and a mix of many kinds of ice. Most of the ice in the comet nucleus is water, carbon dioxide, methane and ammonia ices. They also have traces of several other ices that contain carbon, nitrogen, oxygen and hydrogen, especially cyanide, carbon monoxide, HCO (a violently reactive ion in the aldehyde group), all of which are highly toxic organic molecules. Scientists first discovered that these toxic chemicals were in comets in the 1880s and 1890s. When astronomers predicted Earth would pass through the tail of comet Halley in 1910, many people panicked about these gases, but comets are so small, no one would’ve been poisoned, even it the entire comet had landed in the back yard.
When the comet gets close to the sun the exposed ices sublimate (go straight from solid to gas). The gas escapes the nucleus in jets and forms a cloud around the nucleus – the coma. The European Space Agency’s Rosetta mission caught this image showing many jets coming off the sunlit side of Comet 67P/Churyumov-Gerasimenko in 2015.
The lightweight gases are swept away from the comet by the solar wind, forming the straight, blue, dim ion tail.
The ice acts like glue, holding the comet together. As the ice sublimates, the silicates, carbon chunks and heavier particles a released and drift off behind the comet, forming the dust tail. Note that the ion tail always points away from the Sun, but the dust tail always points back the way the comet came, so the tails can point in completely different directions! Rolando Ligustri caught the two tails of comet Garrard as it passed a star cluster in 2012.
These particles eventually spread out along the comet’s orbit, and if Earth passes through that stream we get a meteor shower. Sometimes enough ice will sublimate that the comet will actually break apart when it passes the Sun or Jupiter, which is what happened to comet Shoemaker-Levy 9 in 1994.
Materials for making a comet model:
- Model Magic or similar modeling compound in white and/or light blue to simulate the ices. Each comet needs a glob 2 – 5 inches across.
- Dirt, potting soil, sand, glitter, or other material to simulate the sand and carbon particles
- (optional) beads or small stones to simulate larger rocks.
- Blue and white or iridescent curling ribbon.
- a couple pencils
- Smash the glob of modeling compound flat.
- Sprinkle it with a THIN layer of dirt/glitter/etc.
- Roll it up like a jelly roll to keep the dirt/glitter/etc inside.
- Reshape it to be roughly round.
- Repeat steps 1 – 4 until you are happy with the amount of stuff in the nucleus.
- Reshape it to be whatever shape you want your final comet to be.
- Use your fingers or the pencils to make craters and lumps on the surface.
- (optional) stick a few small beads or stones to the surface.
- Add the ribbon to make the tails. Remember, the comet actually has two tails, which could be side by side if the comet is approaching the Sun, or on opposite sides if the comet is leaving the Sun.
The original version of this activity was created and developed by Laura Venner. You can find it at http://www.laurajeanchecki.com/educator-resources/model-magic-comets/
Take the next step:
- Check out these tips for observing the Perseid meteor shower.
- Learn about the body with this free printable matching card game.
- Try this DIY activity to learn about meteors and craters.
The University of Michigan Department of Astronomy may have established one of the first research observatories in the Midwest more than 150 years ago, but more than anything, it’s a young and vibrant department. That’s because we’ve spent the last decade hiring exceptional faculty, investing in high-profile facilities, and restructuring our curriculum — all to propel our graduates into the top ranks of the field.
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