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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

Distance from Sun in parsecsnumber of starsstars/cubic parsec

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 an Astrophysicist

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