How much star light does the universe produce?

[Javid]

If the Sun were just an ordinary "light bulb" illuminating the Earth and the rest of our solar system with visible light, and you were to simply switch it "off" at this very moment in time, anyone here want to guess how much light the whole starry night sky would then produce? (That's an accumulation of light from every star, every galaxy, every globular cluster, the whole Milky Way's glow, and every source of incandescent glowing gas in every nubulae... everything in the entire universe!)?

Jav
:o

[antoniseb]

Originally posted by Javid@Dec 20 2004, 12:57 PM
anyone here want to guess how much light the whole starry night sky would then produce?
Are you talking only about light that is in the optical range when it gets to us? Are you counting the light that gets absorbed by dust and stellar interiors before it can get to us?

If that's what you're counting, I'd guess that it would be about as bright as a magnitude -2 or -3 star. So about one billionth as much light as we get from the sun.

[John L]

Probably about the same as what we see on a regular night. The Appollo astronaughts, on the far side of the Moon shielded from the Sun, didn't see much of an apparant increase in starlight.

[Betelgeuse]

Yeah, I totally agree with John L. Step outsided on a cold night, let your eyes ajust to the darkness - the outlook will look the same. Think about it - think how far out we can see from - we look out at night and see the Milky Way - our galaxy and of course, with the odd exception - andromedia etc. "Switching off" the sun won't increase our ability to see further out into the universe much at all......

Hope this helps
Regards
Rigel

[antoniseb]

I think the point that Javid is making is not that the sun has to be off, but rather to estimate the amount of light from all other sources. You may note that in a previous post in another thread he referred to a place a few tens of thousands of AU away from the Sun, where illumination from the sun was equaled by the light of everything else.

While I don't think there is a special significance to this sphere physically, or operationally for a spacecraft, it is an interesting place to think about.

[Javid]

Antoniseb - sir - you are very right.

You don't actually have to turn the Sun "off", you can just go a couple of light years away into deep space (from where the Sun looks just like another star) and take a measurement of the cosmic night sky.

Our man - captain Ahab, no, that should be Ahad, did this in his night sky paper by using some magnitude adding equations. He came to a net figure of -6.5 or roughly 1/300th of a full moon ("Ahad's constant"). His workings are here:

http://uk.geocities.com/aa_spaceagent/rest...terstellar.html (http://uk.geocities.com/aa_spaceagent/restricted/interstellar.html)

So there's a new constant that will be added to the Astronomy books, hopefully soon.
Wanna see what the Sun looks like from Alpha Centauri? Here's a sim:

http://uk.geocities.com/aa_spaceagent/sunb...brightness.html (http://uk.geocities.com/aa_spaceagent/sunbrightness.html)

It's quite a humbling thought to know that our majestic Sun, the giver and sustainer of all life to our planet and all that we ever experienced and knew about, could be cast aside into no more than a bright twinkling dot of starry light, just like that. I can't wait to go on a voyage to the stars...

Jav
:D

[downunder]

This "constant" is only a local constant. Imagine what it would be if the Earth was circling a star somewhere near the core of the galaxy. Or if we were inside a dust cloud. Or anywhere else except where we are now.

[Javid]

"Ahad's constant" will stay as a fixed constant within a sphere of several hundreds of light years in radius centered on Sol - providing one is not located too close to a particular star within this zone.

(Oh, and also the occasional transient flaring of a supernova in local galactic space can cause a small _momentary_ fluctuation.)