Hi Jonathan,

Astronomers, by looking at the light from many, many stars in our galaxies, know that all the stars are rotating around "the center" fo the galaxies. They can tell about the star's motion because the color of the light get shifted slightly by the motion. So astronomers can estimate what point all the stars are rotating around. This is just one way of estimating the distance. Astronomers also use "standard candles". A standard candle is an identifiable type of stellar objects (such as the best known type of supernova aka stellar explosion) who intrinsic brightness is know. Then, from how bright it appear, its distance can be estimated.

The distance is still uncertain but is thought to be 25,000-28,000 light years away.

Paulett