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Light and the Formation of Shadows

Emission of light

Sources of Light

The two brightest objects we see in the sky are the Sun and the Moon. The brightness of the Sun is so high that during day time, the Moon is not visible in the sky. During night, when the Sun has set, we can see the Moon. Apart from the brightness of light, is there any other difference between sunlight and moonlight?

The answer is YES. There is a big difference between the two. The Sun emits its own light, whereas the Moon does not have its own light. The Moon is illuminated by sunlight. So, what we call moonlight is basically reflected sunlight.

Like the Sun, candles, light bulbs, kerosene lamps also emit light. So, these objects are different from the objects that do not emit light. Therefore, all objects can be classified into two categories—luminous and non-luminous.

The objects that emit their own light are known as luminous objects. The Sun, candle, stars are all luminous objects.

The objects that do not emit their own light are called non-luminous objects. Chairs, tables, clothes, etc., are all non-luminous objects.

In normal temperature, many objects are non-luminous; but many of them can become luminous when raised to higher temperatures. In normal temperature, you will find that an iron rod does not emit light and thus, is a non-luminous object. When you heat the same iron rod to a very high temperature (near 1000°C), you will find that the iron rod becomes red hot. You will observe light being emitted from the rod. Therefore, at high temperature, the iron rod become…

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