Lesson Plan D2 • 1 spoonful of rubbing alcohol or ammonia

(window cleaner will do)

Comets and • 10-20 plastic bags (grocery bags with
NO HOLES)
Meteors • Plastic dishpan or other large plastic
container
• Plastic bowls or large ice cream containers
(enough for each group of students)
Introduction • Wooden or sturdy plastic spoons (not metal!)
for mixing
Comets have always fascinated people because • Thick winter gloves
of their unpredictability and their beauty. At • Hair dryer or lamp with an exposed bulb
one time they were seen as omens of evil. Later • Protective eye goggles
they were viewed as beautiful but harmless • Cloth towels
objects. Now we know they are a bit of both. • Hammer

In this lesson, students will learn what comets

are made of and a little of how they behave. Time Required
Students will build a model that mimics the
composition of a real comet nucleus. After making Hands-on Activity: 40 minutes
the model comet nucleus, students will use the Starry Night Computer Exercise: 20-30 minutes
Starry Night computer exercise to “hitch a virtual
ride” on a comet as it orbits the Sun.
Conceptual Background
Key Concepts Both comets and asteroids are small solar system
bodies. They are both dark in color, irregular in

Comets are mostly made of dirt and ice. shape, and made of ancient material from the

Comets are often called dirty snowballs or formation of the solar system. They differ in their
icy mud balls. compositions and orbits. Asteroids are composed

A comet develops a tail when it gets close mainly of rock and metal, while comets are
to the Sun. made of ice and rock. Asteroids tend to have

A comet’s tail always points away from near-circular orbits that lie in the plane of the
the Sun. solar system. Comet orbits are very elongated

Meteor showers are caused when Earth and are usually not in the plane of the solar
moves through the debris left behind by system. Comet material has not changed since
comets. the formation of the solar system.

Comets move in elliptical orbits with
random orientations. Comets move in random orbits around the

Most comets come from the Oort cloud Sun. This means their orbits can be tilted in all
at the outer edges of the solar system. directions with respect to the plane of the solar
system. Most comets orbit the Sun in a distant
outer region of the solar system called the Oort
Materials Required cloud. The Oort cloud is a spherical shell of comet
nuclei that surrounds the entire solar system.
• 2 kg (4-5 pounds) dry ice (it can be wrapped New comets are completely unpredictable.
in newspaper and stored in a picnic cooler) Every once in a while something happens to
Note the SAFETY WARNING in the Activity nudge a comet out of it’s place in the Oort cloud
section below. and it begins its long, slow fall inward toward
• 2 liters (quarts) of water the Sun. A comet can approach the inner solar
• A handful or two of soil system at any time and from any direction.
• 2 spoonfuls of molasses, dark corn syrup or
pancake syrup

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If a comet collides with a planet, it is very 1. In the dishpan or large plastic bowl mix
destructive. Comets have struck Earth repeatedly together about one half liter (one half quart)
over Earth’s history. Much of the water in Earth’s of water, half of the dirt, and all of the
oceans may have come from comets. syrup, ammonia or rubbing alcohol.

As a comet approaches the Sun and develops a 2. Line the ice cream containers with plastic
tail, it also sheds small particles of itself. These bags. There should be enough for each group
particles stream out behind the comet and form of students to have one.
a debris stream in the comet’s orbit. If the comet’s
orbit crosses Earth’s orbit, this debris stream can 3. Divide the muddy-water mixture up
produce a meteor shower. between the lined plastic containers.

4. Have everyone put on gloves and goggles.

5. Place your dry ice in a double plastic bag.

Wrap it completely in the cloth towel and
put it on the ground.

Ion tail 6. Use the hammer to smash the dry ice into
tiny pieces.

7. Pour equal amounts of the crushed dry ice

into each of the lined ice cream containers
Dust Tail with the water-dirt mixture. It will make
lots of vapor.
Coma
8. Use wooden or plastic spoons to stir the
Nucleus Head mixture. Keep stirring until it gets thick.

9. Lift the plastic bags out of the containers.

10. Using gloves, pack the slush (still in the

Figure D2.1 plastic bags) into balls. Keep packing until
These are the main parts of a comet. you have a solid frozen lump.

11. Remove the lumps from the plastic bags.

Activity
12. Sprinkle more dirt onto your comets. Pour
This is a messy activity best done outdoors. water over them until they have a frozen
Certain safety precautions must be followed layer of water all over them.
during this activity.

SAFETY WARNING: Now you have some comet nuclei. Watch what
Dry ice is -79 degrees C (-110 degrees F). Even happens to them. Watch them hiss and pop as
brief exposure will cause “burns.” Be careful the dry ice sublimates from a solid to a vapor.
when handling it. Always wear gloves to protect
your hands, and safety goggles to protect your You can speed up the process with a hair dryer
eyes. or other heat source like a lamp. Your comet
nuclei are most impressive outdoors in bright
This recipe makes a scientifically accurate sunlight where they may form a small coma or
model of a comet nucleus. Comets are made of vapor cloud around themselves. Carry (with
frozen water, ammonia, organic (carbon-based) gloves!) your comets around and see if you can
material, and silicates (dirt). see them forming tails.

Starry Night High School D2.2 www.starrynight.com

Discussion Questions comet’s orbit. This in turn makes predicting a
comet’s path through space difficult.
A. Describe the surface features of your comet
nucleus. As you watch your model comet, you may
notice that it hisses and pops more where there
B. Why does the model comet nucleus hiss and pop? is more of the dark-colored dirt. Dark material
absorbs more heat energy from the Sun than does
C. What effect might jets of gas bursting from a light-colored material. These darker areas are
comet nucleus have on the comet’s motion? where the comet surface heats up the quickest
and more dry ice sublimates into gas. A comet
D. If the comet was made entirely of ice with without the dirt wouldn’t be as active or as
no dirt, would it behave the same way? interesting as a comet with lots of dirt. As your
model comet sits around, its surface will become
E. How might a comet appear different when it more cratered and irregular as the dry ice
is far from the Sun compared to when it is sublimates away.
close to the Sun?
When a comet is far away from the Sun’s light
and heat, it stays frozen. It has little or no coma
The model comet nuclei should be irregular and and no tail. As it nears the Sun and is subject
lumpy. As the dry ice is heated it sublimates, or to more solar radiation, its frozen gases begin to
converts directly from a solid to a gas. As it does sublimate more and more. Gas jets release bursts
this, small pockets of gas are released explosively of comet material and the comet develops its
from the comet nucleus. This is why it hisses tail. As the comet continues in its orbit and moves
and pops. When this happens to a real comet, away from the Sun, its tail and coma shrink.
the gas jets make the comet nucleus tumble in The tail and coma reform every time the comet
space. The tumbling makes small changes to the approaches the Sun.

Starry Night Computer Exercise

Lesson D2: Comets and Meteors
why two different parts of the comet gave such
Since antiquity mankind has looked at comets with different results.
awe and wonder. This exercise allows students to learn
some basic facts about the nature of comets and how Comet Halley has been observed over many returns.
they orbit the Sun. Unfortunately the giant planets can affect the comet’s
orbit sufficiently to make predictions of its return only
Teaching Strategies approximate. In this exercise such planetary effects
are ignored and hence predictions of the comet’s
Many students believe that comets come from “way out return far into the future are unreliable.
in space”. While this may be true, they are members
of our solar system. Students are probably aware of the Perseid meteor
shower in mid-August every year. This shower, however,
Students may be interested to know that in the last is caused by debris from a different comet.
century the Earth has probably “collided” with a
comet twice. In 1910 the Earth passed through part Students usually have misconceptions as to the size of
of comet Halley’s tail without any negative effects. “shooting stars”. Most “shooting stars” or meteors are
And in 1908 a small cometary nucleus may have caused by particles no bigger than a grain of sand.
collided with the Earth in Tunguska in central Siberia
causing devastation over an area of about 5000 square This exercise should take students about 20 to 30
kilometers. Students should be encouraged to suggest minutes to complete.

www.starrynight.com D2.3 Starry Night High School

Conclusion Lesson Specific Resources
At the end of this lesson, students should have SkyGuide
a good understanding of what real comets are Guided Tours>Our Solar System, the Stars and
made of. They should know how a comet’s Galaxies> Meteor Showers (all sections)
composition affects its behavior as it approaches
Guided Tours>Our Solar System, the Stars and
and draws away from the Sun in its orbit. They
Galaxies> The Comets (all sections)
should know that most comets move in very
elongated orbits around the Sun, and they spend Guided Tours> Our Solar System, the Stars and
most of the their time far away from the Sun. Galaxies> The Planets> Jupiter> A Comet
Comes to Call

SkyTheater DVD
Main Menu: Earth Zone>Meteorites
Main Menu: Planet Zone>Oddballs

Starry Night High School D2.4 www.starrynight.com

Starry Night Computer Exercises Name:
Lesson D2: Comets and Meteors Class:

Instructions for the Student

Open the SkyGuide pane, and navigate to Student Exercises > D – Asteroids, Comets and Meteors > D2: Comets and
Meteors and follow the instructions given. Record your answers to the questions in the spaces provided.

Ask your teacher for a worksheet if you plan to do the Extra Credit exercise.

Question 1: They came from outer space

a) Describe what the comet looks like.

b) List two things that happen to the comet’s tail as it passes the Sun.

c) In what direction does the comet’s tail always face?

Question 2: A famous comet

a) Describe the size and shape of the comet’s orbit.

b) What is the date? (Only the year is important)

c) During what year was the comet closest to the Sun?

d) Does the comet maintain its speed as it orbits the Sun? Describe and explain any differences.

e) How long does it take Comet Halley to go once around the Sun?

Continued next page

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Lesson D2: Comets and Meteors

f) Predict when comet Halley will be close to the Sun again.

Question 3: Meteor showers

a) On what dates (approximately) can we expect a meteor shower?

b) Does comet Halley have to be near the Earth to give us a meteor shower? Explain.

Extra Credit

a) Use this chart to compare the similarities and differences between comets and asteroids.

Asteroids Comets

Size

Appearance

Composition

Location of orbit
in solar system

Circular or elliptical orbit

Orbital inclination compared

to plane of solar system

Short or long period of orbit

b) Determine the orbital period of Comet Wild.

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