Sun, Moon, and Stars: Astronomy for Beginners · Part II, Ch. IV · Part 2: Part II: A closer look at the Solar System
16. More about the Moon: phases and eclipses
Goal: Your child can show the Moon's phases with a lamp and a ball, explain earth-shine, and tell the difference between an eclipse of the Sun and an eclipse of the Moon.
You'll need
- The book, open to Part II, Chapter IV
- A lamp with the shade off, in a darkened room
- A white ball (a foam ball on a pencil, or an orange)
- The Moon diary
What's in the book
The Moon has almost no air, likely because her weak pull could not hold it. The chapter compares her size and weight with the Earth's, explains earth-shine, walks through the phases from new moon to full and back, shows them with a candle and a ball held at arm's length, and explains eclipses of the Moon by the Earth's shadow.
The lesson, step by step
Look at the Moon diary
Open the Moon diary. Lay out the drawings in order. Ask: What pattern do you see? Does the bright part grow from one side?
Read together
Read the chapter aloud, up to the candle-and-ball experiment.
Make the phases
Do the book's experiment with a lamp instead of a candle. Your child holds the ball out at arm's length, a little above their head, and turns slowly to the left on the spot, watching the ball.
Facing the lamp: the lit side is turned away. New moon.
A quarter turn: half of what you see is lit. First quarter.
Back to the lamp: the whole face is lit. Full moon.
Another quarter turn: last quarter. Then new moon again.
Let your child name each phase as it appears and match it to a Moon diary drawing.
Eclipses with the same ball
Hold the ball exactly between your eye and the lamp: it hides the lamp, a 'Sun' eclipse at new moon. Hold it exactly behind your head, away from the lamp: your head's shadow falls on it, a 'Moon' eclipse at full moon.
SayUsually the ball passes a little above or below. That is why eclipses don't happen every month.
Earth-shine
Read the book's part about the faint glow on the dark part of a young crescent Moon. Say: That is sunlight bounced off the Earth, onto the Moon, and back to us.
What we know now
The book's figures for the Moon's size and weight are right. It is about a quarter as wide as the Earth and about one eightieth as heavy.
The Moon does have a trace of gas around it, but so thin it is almost nothing, just as the book says.
In a total eclipse of the Moon, it often turns a coppery red. That is sunlight bent through the Earth's air, the light of all the world's sunrises and sunsets falling on the Moon. Eclipses of the Moon are completely safe to watch with your eyes, binoculars or a telescope.
Tell it back
Ask your child to teach the phases to someone else in the family with the lamp and ball.
Check questions
At what phase can an eclipse of the Sun happen? An eclipse of the Moon?
What is earth-shine?
Why does the Moon have no air to speak of, according to the book?
Afterwards
Keep the Moon diary going. Look up the date of the next eclipse of the Moon visible where you live and plan to watch it.
Tip
A foam ball stuck on a pencil gives a handle, so the hand doesn't cast a shadow on the 'Moon'.
Answers to the book's problems
An eclipse of the Sun at new moon; an eclipse of the Moon at full moon. Earth-shine is sunlight reflected from the Earth onto the dark part of the Moon, and back to us. Because she is so small that her pull was too weak to hold the swift gas particles, so they slowly escaped into space.
Worked out for this site from the scan. If a number in your copy differs, trust the book.