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Take a spaceship in interstellar space, say halfway between Sol and Alpha Centauri. So, you have what is effectively a sphere of stars around it providing all the illumination - how bright would this be? Is starlight alone bright enough to cast shadows?

Next time you're in the countryside away from city lights..

go outside and stand in any farm-field on a moonless night.

That will give you an idea.

Actually, the answer to your question of course is "yes".
All light casts shadows.
The question is: "is the human eye sensitive enough to see the shadows cast by starlight?"

Don't forget that there are thousands of stars casting shadows, too. That'd make it very hard to detect the individual shadows.

let me rephrase: if you could figure an average apparent magnitude for all the stars in a 360 degree sky, what would it be? I figure it'd be about 5 or 6?

Malenfant wrote:let me rephrase: if you could figure an average apparent magnitude for all the stars in a 360 degree sky, what would it be? I figure it'd be about 5 or 6?

You might like to try Mostly Harmless. I haven't used it myself, but I understand it has a database of stars built in mySQL, so a simple SQL query should answer your question, at least for Celestias/MH's star database.

I don't really see how that would help me...

I guess it does boil down to this: 'is the human eye sensitive enough to see the illumination on an object provided by a full sphere of starlight if that's all there is to see' - not just to see the shadows cast by it. Would the starlight effectively provide some level of ambient illumination?

I've never been out in a perfectly dark environment with no city lights, a perfectly clear sky, and nothing but stars out. Let alone one where I have stars not only above me but below me too. So references to such things aren't particularly useful .

Yes, you can see by starlight, but not colors.

I found a paper on human vision response to various light levels titled "Fundamentals of Spatial Vision" by James A. Ferwerda at http://www.graphics.cornell.edu/~jaf/pu ... _final.pdf


Section 3 includes a scale of relative light levels from starlight to noon and how the eye adapts to them.

Now THAT'S what I'm talking about. Thanks, Selden!

Malenfant wrote:Take a spaceship in interstellar space, say halfway between Sol and Alpha Centauri. So, you have what is effectively a sphere of stars around it providing all the illumination - how bright would this be? Is starlight alone bright enough to cast shadows?

My fellow Stephen Baxter fan who must have really enjoyed the Manifold Time and Space books....I must say to you that it will be very very very bright!

Space is alot brighter, busier, and happening than we earthlings may figure just from looking up there from here...

he he he he..

I don't know if this will answer your question, but it's an interesting read:

http://www.astropix.com/HTML/L_STORY/SKYBRITE.HTM

Lone

It should be possible to compute a rough magnitude by summing the light output for all the stars.

The amount of light contributed by a star is equal to 10^-(m*2/5), where m is the apparent magnitude of the star. Then add up all the result for individual stars, and convert back to a magnitude with logs: -5/2*log10(sum).

When the brightnesses of the 25 brightest stars are summed in this way, the resulting combined magnitude is about -3.14. By comparison, Venus can be as bright as -4.4.