Sun, Moon, and Stars: Astronomy for Beginners · Part II, Ch. VII · Part 2: Part II: A closer look at the Solar System
20. Jupiter, the giant
Goal: Your child can describe Jupiter's belts and four large moons, and can watch the moons change places from night to night.
You'll need
- The book, open to Part II, Chapter VII
- Binoculars and something steady to lean on (a fence, a car roof, or a tripod)
- A notebook for a Jupiter-moon log
- A watch, to show which way 'west to east' goes
What's in the book
Jupiter is huge and spins in about ten hours. The chapter describes its light and dark cloud belts, its fierce winds, the guess that it might still be hot inside, and its moons: a tiny new fifth moon found by Professor Barnard, and the four large ones, Io, Europa, Ganymede and Callisto. A side passage explains the plane of the ecliptic with a sheet of cardboard and a watch.
The lesson, step by step
Read together
Read the chapter aloud. At the cardboard-and-watch passage, lay a watch face-up on the table. Say: The planets go round the Sun the opposite way from these hands, seen from above the north.
Draw Jupiter
Draw a slightly squashed circle (the book says Jupiter is flattened at the poles because it spins so fast). Color light and dark stripes across it. Add four dots in a line beside it for the moons.
Watch the moons yourself
Look up whether Jupiter is in the evening sky (it is usually the brightest 'star' in the sky after Venus). Hold the binoculars very steady, and you can often see up to four tiny points of light in a line beside it: the moons Galileo first saw in 1610.
Draw what you see in the Jupiter-moon log. Look again the next clear night: the moons will have moved.
What we know now
Jupiter has no solid surface to stand on. It is mostly hydrogen and helium, getting thicker and hotter deeper down. The book's guess that it is hot inside was partly right: Jupiter gives off a little more heat than it receives from the Sun. But it is not cooling toward a solid crust.
Its Great Red Spot is a storm wider than the whole Earth that has blown for centuries. Its winds can go faster than 300 miles an hour.
Spacecraft have visited many times. Io has hundreds of volcanoes; Europa hides an ocean under its ice. Callisto is just a little smaller than Mercury, not larger. And Jupiter has about a hundred known moons, not five.
Tell it back
Ask your child to describe Jupiter's four big moons from the book: which is nearest, which is biggest, how long each takes to go round.
Check questions
How long is a day on Jupiter?
Why does Jupiter have almost no seasons?
How does the book know Jupiter does not shine by its own light?
Afterwards
Keep the Jupiter-moon log for a week. Number the moon dots and see if you can guess which one is Callisto (it strays farthest from Jupiter).
Tip
Binoculars braced against something solid make all the difference. Even a tripod adapter for a few dollars helps.
Answers to the book's problems
Nearly ten hours (a five-hour day and a five-hour night, as the book puts it). Because its axis is tilted only a tiny amount. Because Jupiter casts a shadow that eclipses its moons; a body shining by its own light would not throw a dark shadow in sunlight.
Worked out for this site from the scan. If a number in your copy differs, trust the book.