Sun, Moon, and Stars: Astronomy for Beginners · Part I, Ch. VII · Part 1: Part I: Our family in the sky, and its neighbors
8. Visitors: the comets
Goal: Your child can describe the parts of a comet, explain why its tail points away from the Sun, and tell the story of Halley's Comet.
You'll need
- The book, open to Part I, Chapter VII
- Paper and pencil
- A fan or a hair dryer on its cool setting, and a strip of tissue paper
What's in the book
Comets once frightened people, who thought a collision would end the world. The chapter explains the head (nucleus and coma) and the tail, the three kinds of comet paths, why tails point away from the Sun, and the comets of Halley, Encke and Newton.
The lesson, step by step
Read together
Read the chapter aloud. Enjoy the story of the shopkeeper family who fled to America to escape a comet. Ask: Was that a sensible thing to do?
Name the parts
Draw a comet together: the bright nucleus, the hazy coma (the 'hair' around it) and the long tail.
The word "comet" means "a hairy body," the name having been given from the hairy appearance of the light around the nucleus.
Draw a comet's path
Draw a dot for the Sun. Around it, draw a nearly round loop for the Earth's path. Then draw a very long, thin oval that passes just inside the Earth's loop at one end and stretches far off the page at the other. That is a comet path like Halley's.
SayThe comet rushes fast when it swings close to the Sun, then creeps slowly far out past Neptune. (You will draw ovals the book's way, with pins and thread, in Part II.)
Why the tail points away
Hold a strip of tissue in front of a fan or a hair dryer on cool. Walk the tissue around the fan in a circle. It always streams away from the fan, whichever way you walk.
SayThe Sun is like the fan. Its light and a wind of tiny particles from it push the comet's tail away.
What we know now
A comet's nucleus is like a dirty snowball: a lump of ice, dust and rock usually a few miles across. Near the Sun the ice turns to gas, making the coma and tail.
Halley's Comet came back as predicted, last in 1986, and is due again in 2061.
Comets can collide with planets: pieces of one comet crashed into Jupiter in 1994. But scientists watch the sky, and no known comet is on its way to hit the Earth.
Tell it back
Ask your child to tell why people were once afraid of comets, and what comets really are.
Check questions
Which part of a comet is the heaviest?
How long does Halley's Comet take to go round the Sun?
Name the three kinds of comet paths the book describes.
Afterwards
Work out with your child how old they will be in 2061 when Halley's Comet returns. Write it in the planet chart or Moon diary.
Answers to the book's problems
The nucleus (the bright head). About 76 years. Closed oval paths that bring them back; paths so long that we cannot tell if they close; and open paths of visitors that pass once and never return.
Worked out for this site from the scan. If a number in your copy differs, trust the book.