Illuminating

[Bazile]

Someone asks why when in space and view the earth , space all around it in all direction is dark - why isn't the light rays from the sun lighting the area immediately around the earth ?

[EDDIE51]

Light has to 'land' on something to illuminate it.
Think of a dark room and you have a torch, you only see the light where it 'lands' on the wall or floor. You don't see the air around the room 'lit up'.
So from space you only see the Earth itself lighted not the surrounding atmosphere or the vacuum of space.

[ToraToraTora]

gawd elp us!

[jim360]

Never ever ever go into a classroom TTT if all you do is poke fun at people for asking questions.

[jim360]

Further to Eddie's answer, I suppose you could also say that, to a first approximation, light rays travel in straight lines. So if you are looking at the sun you will see sun light. And, if you aren't looking at the sun, you won't see it, because the light rays were heading in a straight line away from it. So it need to bound something in order to head in a different straight line to reach your eyes, as eddie said. (Basically I'm just adding "because light travels in straight lines if there's nothing to stop it" to his answer.)

[Bazile]

EDDIE51 - That's a good explanation .

I was trying to explain the reason to the person asking , but she could not see it .

[jim360]

"I was trying to explain the reason to the person asking , but she could not see it . "

I guess your explanation was also travelling in a straight line while she wasn't looking then. :/

[Bazile]

It looks that way jim :-)

[bhg481]

Only when the light is scattered off dust particles in the atmosphere divebuddy.

[jim360]

Yeah there's lots of space dust, but it's also very thinly spread, so that to all intents and purposes space is a vacuum. Or a near-perfect one, anyway.

In the 90 million mile-long journey from the sun to Earth, I should expect that only the tiniest, tiniest fraction of the light from the Sun is scattered by cosmic dust. That just doesn't register, you'll never be able to see it. You're talking individual photons. For the torch in a dusty room, it's still a small fraction (if the light's going to be any good -- as you say, a super-dirty sea and all the light scatters in a few metres), but far, far more appreciable.

It's a question of scales, in other words.

[bhg481]

There are things floating around in space but they will be fairly evenly distributed, so the light reflected from them will form a faint background illumination not readily visible. Water, particularly dirty water, scatters/absorbs light just as dust in the atmosphere does, hence the visibility of the beam and the limit of its penetration..

[jim360]

Not without more information. On a sunny day, I assume, both effects are true? Also, how deep is the water in either case?

Sunlight can penetrate the water, anyway. If it's clean water it can carry on down almost indefinitely. So in that sense I suppose the point is that the high tide, and motion of the water, changes the concentration of the sand to the extent that light can penetrate to the depth you are lying -- but only for a split second in any one direction, which gives you the glittering effect.

In still, murky water, this motion doesn't happen and the light is stuck "above" the band of silty sandy yeuch.

[wildwood]

Think of it as if two inmates are trying to escape over the wall of an asylum.

A says two B "I got a torch, you climb on the light beam so you can get over the wall".
"No way" says B. "I know you...... when I get half way up you switch the torch off and I'll fall".

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Yes, I'll get my coat.....