On Jan 13, 7:44*pm, "Mark Earnest" wrote:
"Greg Neill" wrote in message

m...



Roedy Green wrote:
In a *75 light year radius sphere centered on earth have you an
estimate how many stars and planets there are, or could you give me
density numbers I could use to compute that?

There are about 50 known stars within 16 light years:

http://www.cosmobrain.com/cosmobrain/res/nearstar.html

So that equates to a density of about 2.9 x 10^-3 stars
per cubic lightyear. *For a radius of 75 light years that
translates to about 5,000 stars.

As to the number of planets, you'll have to dig up an estimate
(or make a guess) as to the fraction of stars that have
planets.

Well, with the number of planets they are discovering these days by the
Hubble, I would say probably most of them.

Perhaps 10% should be worthy of hosting planets. New and improved CCD/
CMOS imaging with individual pixel well/bucket unloading should help
expose even Sirius C.

~ BG