Density of stars and planets

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?
--
Roedy Green Canadian Mind Products
http://mindprod.com
PM Steven Harper is fixated on the costs of implementing Kyoto, estimated as high as 1% of GDP.
However, he refuses to consider the costs of not implementing Kyoto which the
famous economist Nicholas Stern estimated at 5 to 20% of GDP

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.

"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.

On Jan 13, 7:03*pm, 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?
--
Roedy Green Canadian Mind Productshttp://mindprod.com
PM Steven Harper is fixated on the costs of implementing Kyoto, estimated as high as 1% of GDP.
However, he refuses to consider the costs of not implementing Kyoto which the
famous economist Nicholas Stern estimated at 5 to 20% of GDP

Our 75 ly radius isn't very populated. There are many tightly packed
areas of our galaxy that'll put our local stars to shame, not to
mention what the universe has to offer.

Perhaps 10% of our local stars within 75 ly radius should have
planets, and a few of those planet shouldn't be without moons.

Sirius C is supposedly a 50x Jupiter, and is likely to having
substantial moons or planetoids of its own.

~ BG

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