Sun, Moon, and Stars: Astronomy for Beginners · Part II, Ch. XI · Part 2: Part II: A closer look at the Solar System
24. More about comets: tails, dust and visitors
Goal: Your child can explain why a comet's tail always points away from the Sun, even when it leads the comet, and what comets and meteorites are made of.
You'll need
- The book, open to Part II, Chapter XI
- A flashlight or lamp for the Sun
- A cotton ball and a strip of ribbon or tissue taped to it for a comet
- A dark plate and a magnet in a plastic bag (optional, for collecting space dust)
What's in the book
The chapter tells of famous comets of the 1800s (1811, Halley's in 1835, 1843, Donati's in 1858), how a star shone undimmed through Donati's tail, how Jupiter's moons threw a comet off its path, and how the tail always points away from the Sun, so that a comet going away seems to push its tail in front. It closes with what comets and meteorites are made of and comets that visit from beyond.
The lesson, step by step
Read together
Read the chapter aloud. At Donati's comet, stop: the star Arcturus shone through its tail as if nothing were there.
Tail first, head first
Put the lamp in the middle of the room. Carry the cotton-ball comet in a long loop around it, always keeping the ribbon tail pointing away from the lamp.
Coming in, the tail trails behind. Going round the lamp, it swings. Going away, the tail goes first.
The comet thus appears to be moving backwards.
What we know now
Comets often have two tails: a curved dust tail pushed by sunlight, and a straight, bluish gas tail blown by the solar wind, a stream of electrically charged particles from the Sun. The book's guess that 'electricity may have something of a hand in the matter' was a good one.
In 2014 a spacecraft, Rosetta, orbited a comet and dropped a small lander on it. The nucleus was a dark, dusty lump of ice and rock a couple of miles across.
Meteorites do not come from the Sun or from Earth's volcanoes. Most are pieces of asteroids; a few were knocked off the Moon or Mars by crashes. Today's estimates say many tons of space dust fall on the Earth every day.
Most comets belong to the Sun's family, coming from far out beyond Neptune. But in 2019 astronomers did spot a comet that came from another star, and another visitor from outside the Solar System was found in 2025.
Tell it back
Ask your child to explain why a comet going away from the Sun seems to be pushing its tail ahead of it.
Check questions
How did astronomers know Donati's comet's tail was very thin?
What happened to the comet that passed among Jupiter's moons in 1770?
About how often does Halley's Comet return?
Try it (optional)
Collect space dust: set a dark plate out in the rain or in a gutter's run-off, or rinse rain-gutter grit into a bowl. Dry it, then pass a magnet sealed in a plastic bag over it. Tiny round metal specks under a magnifier may be micrometeorites, though most will be ordinary dust. Wash hands afterward.
Afterwards
Look back at the comet drawing from Part I and add a second, straight tail.
Answers to the book's problems
Because the bright star Arcturus shone through the densest part of the tail, close to the nucleus, without being dimmed at all. Jupiter and its moons pulled it into a completely new orbit, while the comet did not disturb the moons at all. About every seventy-six years.
Worked out for this site from the scan. If a number in your copy differs, trust the book.