Week 27 · Theme 4 Change and Stability, Unit 4 Patterns in the Sky, Concept 4.2 Patterns of Motion in the Sky (B) · 3 lessons
2
Day and night with a lamp and a ball
Discovery Education Science P5: Term 2, Unit 4, pp. 150–156
GoalUse a lamp-and-ball model to explain day and night and the phases of the Moon, and write a claim, evidence and reasoning about day and night.
New words
model · a smaller, simpler copy of something that helps us understand itphase · the shape of the lit part of the Moon that we see from Earthreflect · to bounce light off a surface
Explanation
A model is a safe way to study something big. A small LED lamp is the Sun and a ball is the Earth. The side of the ball facing the lamp is lit (day), and the side facing away is dark (night). Turn the ball slowly and a spot on it moves from light to dark, just like a place on Earth. Now use the ball as the Moon. The Moon makes no light of its own: it shines because it reflects sunlight. Half of the Moon is always lit, but from Earth we see more or less of that lit half as the Moon goes round us. When we see none of it, it is a new Moon. A thin curve is a crescent, half is a quarter, and a whole bright circle is a full Moon. The shadow of the Earth does not make the phases. It takes about a month for the Moon to go through all its phases.
Worked examples
Phase
What we see
new Moon
none of the lit half
crescent
a thin curve
quarter
half a circle
full Moon
the whole lit circle
The five Moons in the first picture of this lesson show new, crescent, quarter, bigger than half, and full, in order from left to right. The Moon takes about 15 days to go from new to full, and about 29 days to go from one new Moon to the next.
In the picture, the Moon is at one place in its orbit, and the Sun is on the left. The half of the Moon that faces the Sun is lit. From Earth we see only part of that half, and the part we see changes as the Moon moves round.
Part
In short
claim
rotation causes day and night
evidence
a spot on the ball goes into and out of light
reasoning
places face the Sun, then face away
Claim, evidence and reasoning for day and night. Claim: Earth’s rotation causes day and night. Evidence: in the lamp model, a spot on the ball goes in and out of light as it turns. Reasoning: as Earth spins, any place faces the Sun for part of the day and faces away for the rest.
Class activity
Lamp-and-ball model (a grown-up helps; use a small LED lamp or torch, not a hot bulb; nobody looks into the light; use a blunt stick or a straw to hold the ball). In a dim room put the lamp on a table. Hold a white ball at arm’s length and slowly turn on the spot. Draw the lit part of the ball at four places in your turn. Which drawings look like a crescent, a half and a full Moon? Write where you are standing in each. Do not look into the lamp.
Practice
1
Why does the Moon shine?
It reflects light from the Sun. It makes no light of its own.
2
True or false: the phases of the Moon happen because the Earth’s shadow covers part of it.
False. We see different amounts of the lit half as the Moon goes round Earth.
3
The row shows the Moon’s shapes in order. The Moon marked ? is between a crescent and a bigger-than-half Moon. What is it called?
A quarter (half of the circle lit).
4
If the Moon is full today, about how many days until the next full Moon?
