[colty72 (OP)]

When we look up at the moon on a clear night we obviously see the sunlight hitting and then reflecting off the Moon. Why do we not see a "beam" of light streaming from the sun towards the moon for example like a torchlight. Hopefully this makes sense and is not a silly question.

[chris]

You do not see a beam of light stretching from the Sun towards the Moon because the light is passing through empty space until it hits the Moon's surface and is reflected towards you.

For something to be visible it must be emitting a stream of photons in your direction so you can see them. If the Sun is illuminating the Moon, those photons are heading towards the moon, not towards you, so you cannot see them.

But, if there were some dust or other particles between the Sun and the Moon, this could scatter or reflect some of the travelling photons, a proportion of which would be reflected in your direction, making the path of the light visible to you.

At rock concerts or in night clubs, the reason that they fill the place with smoke or fog is so that the lasers and lighting effects can be seen. It's the beam bouncing off the particles of smoke that makes them visible.

[colty72 (OP)]

Thanks for the reply. That makes sense.