Vector magnetograph

A vector magnetograph is a type of imaging

solar corona, and gives rise to the phenomena of solar flares and space weather

Vector magnetographs measure the longitudinal (line-of-sight) component of the magnetic field separately from the transverse (image-plane) components, using different aspects of the

Zeeman splitting is caused by the fact that individual atoms are magnetized due to the circulating motion of electrons bound to them. Emission or absorption of a photon changes the magnetic moment of the atom. In a magnetic field, photons emitted with different polarizations gain or lose energy depending on their orientation relative to the surrounding magnetic field, changing the characteristics of the spectral line—some polarization components are blue-shifted or red-shifted relative to the line's reference wavelength

, by a factor proportional to the field intensity.

Specifically, the circular-polarized component of the light is shifted in wavelength proportional to the field strength in the direction of the observer, and the wavelength shift of the vertical and horizontal linearly-polarized components measures the field strength in those directions.

A vector magnetograph works in a very narrow waveband around a single

HMI instrument on board the Solar Dynamics Observatory

will produce a vector magnetogram every few minutes.

The splitting effect is

symmetric

transverse to the line of sight, so the transverse component of the field can only be measured up to a factor of -1: there is a 180° ambiguity in vector magnetograph measurements of portion of the magnetic field that is perpendicular to the line of sight of the instrument.

Notable existing vector magnetographs include the

HMI instrument aboard the Solar Dynamics Observatory

, launched in February 2010.