Sound does not travel through a vacuum. How do we know that light does?
Explain how you can see ordinary nonluminous classroom objects.
Light? Through what medium does starlight reach us?
We see nonluminous objects mainly with reflected light.
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We know that light can travel through a vacuum because of various scientific experiments and observations.
One of the key experiments that helped in understanding the nature of light was conducted by James Clerk Maxwell in the 19th century. He formulated a set of equations, known as Maxwell's equations, that described the behavior of electromagnetic waves. These equations predicted the existence of electromagnetic waves, which include light, and showed that they can travel even in the absence of a medium, such as in a vacuum.
Furthermore, the observation of astronomical phenomena also provides evidence for light's ability to travel through a vacuum. For example, when we observe stars in outer space, the light emitted from them has traveled vast distances through space, which is mostly a vacuum. This suggests that light can indeed propagate through a vacuum.
Now, moving on to the second question about seeing ordinary nonluminous classroom objects, we are able to see these objects primarily because of reflected light. When light from a light source, such as the Sun or a lamp, falls onto an object, it interacts with the surface of the object. Some of the light gets absorbed by the object, while the rest gets reflected and scattered in different directions. This reflected light enters our eyes, and our eyes and brain work together to process the incoming light signals and create a visual perception of the object.
Finally, as for starlight, it reaches us through space without a medium or medium like atmosphere, before entering our eyes. In space, where there is no significant atmosphere or other media, starlight can travel through the vacuum and reach us directly. This is why we are able to observe stars even though they are millions or billions of light-years away from us.