Ramanath Parimi

A magnetograph is a special type of magnetometer the measures the time plot local magnetic field. It records the a time plot automatically.

Early magnetographs were invented by Francis Ronalds and Charles Brooke independently in 1856 that continuously recorded the movements of magnets using photography. [1]

A magnetograph could simply be iron fillings on the card board with a magnet under it. The iron fillings alignments measure the magnetic lines of force.  [2]

The magnetographs (of vector type) has important role in Solar Physics. The astronomers are interested to measure the solar magnetic field as it plays the key role in solar atmospheric structure and solar activity.

There are two types of magnetographs -

  1. line of sight magnetograph (also called longitudinal)
  2. vector magnetograph

The magnetic field is a vector quantity (which has both magnitude and direction). A longitudinal magnetograph measures only the size of the magnetic field directed along the line of sight. The vector magnetograph measures the full vector and gives three quantities as output -

  1. The size of the line-of-sight component
  2. The size of horizontal component
  3. The direction of horizontal component

With these measurements, it would be possible for scientists to theoretically reproduce a mapping of the field which would correspond to the real thing, which would look like below -  [3]

image of dipole magnetic field

Sources and Further Reading -

[1] https://en.wikipedia.org/wiki/Magnetometer#Types_of_magnetometer

[2] https://www.quora.com/How-would-you-show-that-there-is-a-magnetic-field-around-a-magnet/answer/Gangadharan-Jothinathan

[3] https://magnetograph.msfc.nasa.gov/magmore.shtml