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The Question
(Submitted January 23, 1998)
Could you please give me an estimate of the amount of stars located
within 100 light years from earth?
The Answer
As a function of distance, the Gliese star catalog lists the following
number of stars. A parsec is 3.26 light years.
Distance Number Density
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Distance from Sun in parsecs | number of stars | stars/cubic parsec |
| 5 | 63 | 0.120 |
| 10 | | 328 | 0.078 |
| 15 | 1008 | 0.071 |
| 20 | 2127 | 0.063 |
| 25 | 3496 | 0.053 |
http://www.stellarium.com/nearstar/nearby.html
The fall-off in density is probably due to the fact that many stars are too
faint to be cataloged at a distance more than 5 parsecs. (At still larger
distances, the density of stars does vary as you move outside of the local
spiral arm of our galaxy and into the less-populated regions above and
below the disk.)
Using the 0.120 stars/cubic parsec number, and using a volume for a distance
100 light-years = 100/3.26 = 30.7 parsecs
Number = density * volume
= 0.120 stars/cubic parsec * 4/3 pi (30.7 parsecs)^3
= 14,600 stars
Most of these stars are completely unknown.
David Palmer
for Ask a High-Energy Astronomer
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