Re:How did they find out? (Score 2, Informative)

The way they find out is taking a spectrum of the star light. The spectrum, via prisim/spectrial grating tells us what the object is made of, its temperature, ans if an effect knowen as, for give my spelling, Zieman spiliting effect takes place on the spectrial lines, there is a magnetic field present on or applyed to the luminus object. The object can be a star, candle flame, Heated iron, basicly anything that gives off light. All you need is a light source. No great or even mediourcer resoilution necessary, just the bear minuim light.