How light travels

This lesson asks you to name natural and artificial sources of light, and to describe properties of light: that it travels in a straight path and that it can be absorbed, reflected and refracted. The museum offers one scholar's experiments on how light travels and his naming of reflection and refraction among the states of light; the light sources in those experiments include the sun, the moon, a star and a candle. Absorption and sources of your own are for your class to investigate. ¹

The expectations ask for a property of light and for the sources that give it. Think of a test with a source, a small opening and a screen, and of what you would block or measure to check the path.

In Ibn al-Haytham's dark room, sunlight enters through a small hole. In dusty air the light can be seen stretching straight from the hole to where it falls ². Set an opaque body on that line and the light vanishes from the spot beyond; take the body away and the spot returns. Lay a ruler along the line and the light keeps to its edge ³. He says the same holds for the light of the moon ³, and for a bright star on a night without a moon ⁴.

Ibn al-Haytham tried the sun, the moon, a star and candles, and the light kept to a straight line each time. Why is a claim about light more convincing when it is tested with several sources than with only one?

• Ibn al-Haytham's dark room: the sunlight, starlight and candle tests, step by step.
• Optics: the three conditions of light he studied, travelling straight, reflected and bent.
• Ibn al-Haytham: who he was and what else he wrote.

Read about Ibn al-Haytham's dark room. List the sources of light it names, then sort them into natural and artificial.