Expert: Jayendra Upadhye - 8/2/2008

Question
If our sun was reduced to a grain of salt, how many meters away would the next closest star be? I ask because I want to figure out the volume of space occupied if all the stars in our galaxy were reduced to the size of salt grains (perhaps one-half the diameter of our solar system?). Thanks.

martin

Answer
Hi,
I am not going to answer directly.
Consider that the nearest star proxima Centauri is 4.3 light years away.

1 ly is 300000 km/sec * 3600 sec /hr * 24 hrs/day * 365.25 days/ year
or 1 ly = 300000*3600*24*365.25 = 9467280000000 km.

The sun is roughly 1000000 km in diameter. (approx only).

That would mean if 1000000 km corresponds to 0.5 mm (say), then by the rule of 3s, 9467280000000 km would be
9467280000000 km * 0.5 mm / 1000000 km
= 9467280*0.5 mm
= 9467.280 met
= 9.467 km! (say 10 km)
Then on this new scale, Proxima centauri would be
= 9.467 * 4.3 = 40.709 km away!!

If sun became a grain of salt, proxima centauri would be 40 km away!!

The galaxy at 100000 lightyears dia would be 946,700 km wide!!

And the universe would be 14 billion ly * 10km /ly or approx. 14*1000,000,000*10 km wide!!

I leave it to you to weed out approximations.

But there would be no point would there?

Please do rate the answer.


Hi! Thanks for the rating!
However i did find out a very silly mistake that i MUST admit i made, especially as you say you are NOT  maths buff!!

Revised figure after removing mistake is this.
[That would mean if 1000000 km corresponds to 0.5 mm (say), then by the rule of 3s, 9467280000000 km would be
9467280000000 km * 0.5 mm / 1000000 km
= 9467280*0.5 mm] <------------ mistake is from here..

I FORGOT THE FACTOR 0.5 in all my carried forward figures...
Age catches up with you i think!! Despite what one "likes to believe"!!

So..
= 9467280*0.5 mm
= 4733640 mm or 4733640/1000 met
= 4733.640 met
= 4.733640 km! (This is one light year on our new scale).
At 4.3 light years, Proxima centauri the nearest star would be
= 4.733640*4.3= 20.354652 km away
(correct as originally i forgot the 0.5 factor which now rightly halves our readings).

By this token of halving our previous calculations, (sorry about that earlier slip my dear fellow), The milky way at 100,000 light years would be 4733640 km wide!

And the universe at 14 billion lys would be 4.733640*14,000,000,000=66,270,960,000 km wide!
(Almost half the previous value of 140,000,000,000 km).

Despite my silly error Martin, The fact IS that the universe is IMPOSSIBLY empty, YET rich and varied beyond measure, and incredibly massive, yet expanding, and is currently at an CMB (COSMIC MICROWAVE BACKGRUND black body temperature of just about 3 degrees kelvin.

Thanks for your rating anyway.
regards
jayen