If a fine star ruby or sapphire is properly lit, the needles reflect the light in such a manner that it appears the star is hovering over the gemstone. The star wanders as the light is moved. One will have good color and a bad star. One will have a great star and bad color. Only one out of a hundred will have a good star and good color.
Fine stars are pretty rare.
Until the 1960s, these stones always sold for more than the faceted ruby.