stellar density in our neighborhood

I'm curious how many stars are "near" us. That is, within spheres of
radius 5 lightyears, 10 ly, 20 ly, 50 ly and 100 ly...how many stars
within those spheres? Is this stellar density isotropic, that is,
different in different directions, or is it fairly uniform?

I understand our solar system is near the "edge" of our galaxy, the
Milky Way. What would the stellar density be half-way towards to
center, but still in the disk?
--
"If at first you don't succeed; call it version 1.0"

"Bug Dout" wrote in message
...
| I'm curious how many stars are "near" us. That is, within spheres of
| radius 5 lightyears, 10 ly, 20 ly, 50 ly and 100 ly...how many stars
| within those spheres? Is this stellar density isotropic, that is,
| different in different directions, or is it fairly uniform?
|
| I understand our solar system is near the "edge" of our galaxy, the
| Milky Way. What would the stellar density be half-way towards to
| center, but still in the disk?
| --
| "If at first you don't succeed; call it version 1.0"
|
Stellar density is inhomogeneous.
Now that you've learnt "isotropic", try version 2.0.

On 11/08/2010 03:03 PM, Bug Dout wrote:
I'm curious how many stars are "near" us. That is, within spheres of
radius 5 lightyears, 10 ly, 20 ly, 50 ly and 100 ly...how many stars
within those spheres?

There are about 12 stellar objects within 10 year-lights of the Sun,
according to http://www.nova.org/~sol/solcom/stars/s10ly.htm. The
annual handbook of the Royal Astronomical Society of Canada has a
chapter on nearby stars. Unfortunately I've mislaid by copy, so I can't
quote you numbers from that reference. You can order a copy of the
handbook from http://www.rasc.ca. It is a nice book to have.

Bud

In article ,
Bug Dout writes:
I'm curious how many stars are "near" us. That is, within spheres of
radius 5 lightyears, 10 ly, 20 ly, 50 ly and 100 ly

Oppenheimer et al. (2001 AJ 121, 2189) listed 167 stars within 8 pc
(=26 ly) of the Sun and north of declination -35 deg (about 79% of
the sky). However, subsequent, more accurate parallaxes show that a
few of their stars are actually more distant than 8 pc. On the other
hand, some very faint stars were missed by their survey.

Is this stellar density isotropic, that is,
different in different directions, or is it fairly uniform?

For the smaller distances, I don't know any reason the distribution
should be anisotropic. Of course there are statistical fluctuations.

The Sun is about 20 pc above (north) of the Galactic plane (Humphreys
& Larsen, 1995 AJ 110, 2183), so for the larger distances, there will
tend to be more stars towards Galactic south.

I understand our solar system is near the "edge" of our galaxy,

Roughly 8 kpc from the Galactic center. There's no "edge" as such;
the stellar density in the disk drops off exponentially with a scale
length between 3.5 and 5 kpc. (There is considerable uncertainty in
the measurements.)

What would the stellar density be half-way towards to
center, but still in the disk?

That's about 4 kpc or one scale length lower, so the density would be
about 2.7 times larger, but the uncertainty is pretty big, as noted
above. Still closer to the Galactic center, the bulge population
would become important.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

Excellent, thanks a lot. Watched too many reruns of Startrek: Next Gen
and got to wondering just how many other stars are around us.
--
Why is it that when someone tells you that there are over a billion
stars in the universe, you believe them, but if they tell you there is
wet paint somewhere, you have to touch it to make sure?
--Peter Kay

"Bug Dout" wrote in message
...
| Excellent, thanks a lot. Watched too many reruns of Startrek: Next Gen
| and got to wondering just how many other stars are around us.
| --
| Why is it that when someone tells you that there are over a billion
| stars in the universe, you believe them, but if they tell you there is
| wet paint somewhere, you have to touch it to make sure?
| --Peter Kay

Because you can.