How much does a shadow weigh? What? You mean the weight of a shadow but how will you put the shadow on a weighing machine. Wait! What we can do is measure the weight of an object on which the shadow falls. So we have to figure out that casting a shadow on an object can make it any lesser or not. These questions may seem stupid and baseless. But actually these questions have real world implications. The questions we consider useless are topics of study for astrophysicists.

Do you think this question has an answer?    

We have been seeing Peter Pan always fail in catching his shadow. So is there any answer to this question. Well, it is complicated but not beyond our imagination. So don’t feel silly if this question pops up in your mind because there is an answer for it.

Let’s make our concepts of light photons a bit more clear.

How photons are formed?

The central part of an atom is the nucleus. Nucleus is positively charged with protons. However, the neutrons inside nucleus have no charge. Negatively charged electrons orbit the nucleus in predefined positions. Although the electrons are restricted to move from the fixed position but they can do so by changing their energy level. To move into the next lower energy orbit an electron has to lose energy. As electrons move to new orbits energy is released. The energy in the form of energy packets are called “photons”.

Photons have no mass and they travel with the speed of light. As soon as photons escape in air they take up the form of electromagnetic waves or light. Light doesn’t have any mass but it pushes the object a little bit on which it falls. When sunlight falls on Earth, it pushes every square meter of the surface it illuminates with a force of 10⁻⁹ Kg. It doesn’t sound much but the results are significant on large surfaces. In fact, the photons from the sun push the Earth away all the time.  

At night the United states weigh less whereas in day time light pushes away its surface with a force of 14, 925, 122 pounds. The effects matter a lot for astronomers who have to take into account the solar winds. One you escape from the Earth’s atmosphere, light pushing phenomena become more prominent. A space probe travelling from Earth to Mars has to face a pressure of 950 kilometers.

Conclusion  

Now it is proved that shadows don’t have weight. But we can find out the reduction in the weight of an object on which a shadow casts. You can experiment it with your friends. Ask your friend to stand in light and then measure his weight. Similarly, ask him to stand in the shadow of some big object and measure his weight. You will notice that his weight in light is slightly greater than his weight under shadow.

So now you have an answer to the question “How much does a shadow weigh?” Weight of a shadow is zero unless it falls on an object and makes that object a little lighter.