The Fairy-Land of Science · Lecture II, part 3 · Part 2: Lecture II: Sunbeams and the work they do
6. How we see colors, and the work of sunbeams
Goal: Your child can explain that we see a thing because light bounces off it into our eyes, that a leaf looks green because it sends back the green light, and that sunbeams also bring heat.
You'll need
- Sheets of white and black paper (or a white and a black T-shirt)
- A green leaf, a red thing, and a mirror
- A sunny spot
- Optional: sun-print (cyanotype) paper and some lace or a leaf
What's in the book
Pages 42 to 49. How light waves bounce off things into our eyes; why glass is hard to see and a spoon shines; why a leaf looks green; the invisible heat waves in sunlight that lift water, make winds and warm us; and how sunbeams print a picture of lace on special paper.
The lesson, step by step
Hook question
Turn off the light in a room with the curtains closed.
SayWhy can't we see the chair now? It is still there.
Let your child think. (No light is coming from it to our eyes.)
Read together
Read pages 42 and 43, and the leaf on page 44.
So when you say a leaf is green, you mean that the leaf does not want the green waves of the sunbeam, but sends them back to you.
a white tablecloth sends back nearly the whole of the waves, and a black coat scarcely any.
Try it: white and black in the sun
In a dim room, which is easier to see, the white paper or the black? (White: it sends back nearly all the light.)
Now lay both sheets in the sunshine for ten minutes, then touch them. The black one feels warmer, because it keeps the light it takes in and turns it to heat.
Look in the mirror: the light bounced off your face, then off the mirror, back into your eyes.
Sunbeams bring warmth
Read page 46.
Breathe upon your hand, and feel how hot your breath is; well, that heat which you feel, was once in a sunbeam
SayPlants catch sunlight to grow. We eat the plants (or animals that ate them). So the warmth of your body began as sunshine.
Sun pictures
Buckley made a picture of lace on paper soaked in a silver chemical. Don't use those chemicals at home: they stain and sting skin.
If you have sun-print paper (sold for children), lay a leaf or some lace on it in the sun for a few minutes, then rinse it in water as the packet says.
Tell it back and check
Your child explains why a leaf looks green. Then ask:
1. Why can't we see in the dark?
2. Why is a white thing easier to see in dim light than a black one?
3. Which got warmer in the sun, black or white? Why?
What we know now
Leaves soak up red and blue light most and use it to make their food; much of the green is bounced back, which is why leaves look green. Buckley ends by saying the old Greeks worshipped the Sun, and that "We are grateful for the sun instead of to him." Today we know the Sun is a huge ball of very hot gas that shines because of the energy made deep inside it.
Afterwards
Notice it this week: on a sunny day, touch a dark car and a light car (carefully: a dark car can be hot!), or dark and light clothes on a line. Which is warmer?
Tip
Don't hold anything hot near a child's face, though Buckley suggests feeling the heat from a warm iron. The sun on dark paper shows the same thing safely.
Answers to the book's problems
1. In the dark no light comes from things into our eyes. 2. White sends back nearly all the light that falls on it; black sends back very little. 3. The black paper, because it takes in the light and turns it into heat instead of sending it back.
Worked out for this site from the scan. If a number in your copy differs, trust the book.