How do we determine the magnetic Intensity of a celestial body?

Answer 1

Different methods are used for different types of astronomical object. Measuring a remote magnetic field strength is difficult, and often inaccurate. If the object (star or interstellar cloud) has detectable spectral lines, then the Zeeman effect can be used---this is a splitting, or broadening of some spectral lines caused by the magnetic field. For other objects, the magnetic field strength can sometimes be inferred from its effects---for example, in pulsars the magnetic field is extremely strong, and directs a beam of energetic particles.