Why does the moon’s reflection on the surface of a rippled lake appear elongated?
When we see the reflection of the moon or a lamp on lightly rippled water somewhere near us, we notice that in reality each small wave gives a separate image. All illuminated waves together form one figure, which is an elongated spot, the long axis of which lies in the vertical plane passing through the eye and the light source.
To understand how the light path appears, let’s start with a simple experiment.
Sit down at the table, place the mirror M on the table so that the rays of the lamp L, after reflection, fall into your eye. Now place a piece of cardboard under the mirror so that it tilts towards you. You will see that the mirror now reflects objects above the lamp. If you want a ray from point L to fall into the eye, you will need to move the mirror to point N. Now we put cardboard on the other side so that the mirror is tilted in the opposite direction from us, and move the mirror to point N ‘. The mirror in these two inclined positions will represent the extreme positions of the waves at which the light reflected from them will still enter our eye. The distance between N and N * will therefore be the length of the light path. At all points between N and N *, there are sections of waves of this kind that will have a sufficient inclination to reflect the rays towards our eye. The more of these spots, the brighter the light path will be at this point.