Sun, Moon, and Stars: Astronomy for Beginners · Part I, Ch. IV · Part 1: Part I: Our family in the sky, and its neighbors
5. The inner planets and the asteroids
Goal: Your child can name the four inner planets in order from the Sun, say one fact about each, and explain why planets shine.
You'll need
- The book, open to Part I, Chapter IV
- A flashlight and a hand mirror
- Four small balls or wads of paper to stand for planets
- Paper and colored pencils for a planet chart
What's in the book
Planets shine by reflected sunlight, like a mirror in the sun. The chapter sorts the planets into inferior (inside our orbit) and superior (outside), then into two groups of four with the asteroid belt between, and describes Mercury, Venus, Mars and the asteroids, with their years and speeds.
The lesson, step by step
Hook: shining without a light
In a dim room, shine the flashlight on the mirror so it flashes a spot on the wall. Then switch the flashlight off.
SayThe mirror stopped shining. Planets are like the mirror. The Sun is like the flashlight.
A lamp shines by its own light; but a looking-glass, set in the sun's rays and flashing beams in all directions, shines by reflected light.
Read together
Read the chapter aloud. Stop at the book's list of the planets in two groups and copy it onto paper: Mercury, Venus, Earth, Mars, then the asteroids, then Jupiter, Saturn, Uranus, Neptune.
Planet birthdays
The book says a year on Mercury is not quite 88 days, so a person would have about four birthdays for each one of ours.
Work out together: if you are 10 Earth years old, about how old would you be in Mercury years? (About 40.) Mars takes 687 days, nearly two of our years. About how old would you be on Mars? (About 5.)
Hoops on a table
Lay out four balls in a line from a lamp or a 'sun' on the floor: Mercury, Venus, Earth, Mars. Walk each one round in a circle, the nearest ones faster.
SayThe book says the orbits lie almost flat, like hoops on a table, and every planet goes round the same way.
What we know now
The book counts about 350 asteroids. Today more than a million are known.
Pallas is not the largest: Ceres is, about 590 miles across, and it is now called a dwarf planet.
Vulcan, the planet once thought to be inside Mercury's orbit, does not exist.
Venus has no moon, as the book suspected. Mars has two tiny moons, Phobos and Deimos.
The dark patches on Mars are not water but darker rock and dust. Its white polar caps are ice.
Tell it back
Ask your child to name the inner planets in order and tell one thing about each from the book.
Check questions
What is the difference between how a star shines and how a planet shines?
Which two planets are inferior planets, and why?
Why does Mercury have to travel faster than the Earth?
Notice it this week
Venus is often the brightest point in the sky after sunset or before sunrise. Look for it low in the west in the evening or the east in the morning, after the Sun is fully down or before it rises.
Afterwards
Start a planet chart: one box per planet, with its place from the Sun, its year, and one fact. Add the outer planets after the next lesson.
Tip
Only look for Venus and Mercury when the Sun is completely below the horizon. Never sweep binoculars near where the Sun is.
Answers to the book's problems
A star shines by its own light; a planet shines by reflected sunlight. Mercury and Venus, because their orbits lie inside the Earth's. Because it is nearer the Sun, the pull is stronger, so it must go faster or it would fall in. Order: Mercury, Venus, Earth, Mars. Facts from the book: Mercury's year is under 88 days; Venus is nearly the size of the Earth and shows phases like the Moon; Mars is reddish, its day is only about 40 minutes longer than ours, and its year is 687 days.
Worked out for this site from the scan. If a number in your copy differs, trust the book.