The last little goodie is the equation used to determine the distance between two stars.

**DIST = SQRT[ (X1-X2)^2 + (Y1-Y2)^2 + (Z1-Z2)^2 ]**

where SQRT[x] means "take the square root of x", and (x)^2 means "square x".

## Travel Time

If you write a program to generate a list of star co-ordinates, you can then write another to input the list, then find the closest neighbor of each star. Draw lines between them to plot "trade routes" or "exploration routes". Writing a program to list out all the stars within distance X of a given star could also prove useful. Once one has decided how many times faster than light one's starship can travel, it should be easy to use the distance data to determine transit times.

They seem to work, I fed in the co-ordinates of the galactic center and got a point about 10 kiloparsecs on the positive X axis. (RA 17^{h}42^{m}4^{s}, DEC -28°55', DIST 27,000 light years, in case you were wondering.)

## Percolation Radius

Richard Powell has calculated the "percolation radius" for the closest stars to the Sun. The mean distance between stars within 15 light years of the sun is 3.6 light years.