I have three astronomy programs on my computer that give three different distances for Polaris. I just obtained a fourth program, and it says the distance is unknown. What’s the problem?

The center of the stellar merry-go-round
Polaris remains still at the center of star trails.
Bob King

Those new to astronomy expect the distances of bright stars to be very accurately known, but many still aren’t. Different measuring techniques can yield contradictory results. If a star is closer to the Sun than about 50 light-years, astronomers probably know its distance to 1 percent accuracy; farther away, the uncertainty in the value climbs dramatically.

The most reliable distance to Polaris is that published in 1997 by the European Space Agency’s Hipparcos mission: 430 light-years with an uncertainty of ± 30 light-years. This is a distinct improvement on earlier values. It’s important, too,because Polaris is the nearest known Cepheid variable star, the type that has proved quite helpful for gauging the distances to other galaxies.

— Roger W. Sinnott


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