A vector magnetograph is a type of imaging

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe ...

that can estimate the 3-D

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

of the

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

on a distant body with a resolved line spectrum. Magnetographs are useful for studying the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

because the surface magnetic field is important to the creation and maintenance of the

solar corona A corona ( coronas or coronae) is the outermost layer of a star's atmosphere. It consists of plasma. The Sun's corona lies above the chromosphere and extends millions of kilometres into outer space. It is most easily seen during a total solar e ...

, and gives rise to the phenomena of

solar flare A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other solar phe ...

s and

space weather Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the time varying conditions within the Solar System, including the solar wind, emphasizing the space surrounding the Earth, including conditions in the ma ...

. 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 The Zeeman effect (; ) is the effect of splitting of a spectral line into several components in the presence of a static magnetic field. It is named after the Dutch physicist Pieter Zeeman, who discovered it in 1896 and received a Nobel prize ...

that affects the

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

of emission and/or absorption

spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

s in the presence of a magnetic field. The

is caused by the fact that individual

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, and ...

s are magnetized due to the circulating motion of

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

s 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

, 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

, for example the 525.02 nm 'Fe I' line from neutral (non-ionized)

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

. The measured shifts in wavelength are fractions of a

picometre The picometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: pm) or picometer (American spelling) is a unit of length in the International System of Units (SI), equal to , or one trillionth of ...

. Measuring the full spectral profile of the line with this precision requires a high-dispersion spectrograph and a long time to collect sufficient

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...

s to make the measurement with precision. For example, SOLIS requires about an hour to gather polarized spectral profiles over the whole Sun, and Hinode, the recently launched spacecraft with a 0.5-

meter The metre (British spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its prefi ...

solar telescope on board, takes about an hour to cover a 164-arcsecond-square field (1% of the Sun) at very high spatial resolution. Other types of magnetograph use narrowband filter imaging to produce a measurement of the first few

moment Moment or Moments may refer to: * Present time Music * The Moments, American R&B vocal group Albums * ''Moment'' (Dark Tranquillity album), 2020 * ''Moment'' (Speed album), 1998 * ''Moments'' (Darude album) * ''Moments'' (Christine Guldbrand ...

s of the spectral line, and operate much more quickly: the HMI instrument on board the

Solar Dynamics Observatory The Solar Dynamics Observatory (SDO) is a NASA mission which has been observing the Sun since 2010. Launched on 11 February 2010, the observatory is part of the Living With a Star (LWS) program. The goal of the LWS program is to develop the ...

will produce a vector magnetogram every few minutes. The splitting effect is antisymmetric along the line-of-sight, but

symmetric Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definiti ...

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

IVM {{Disambig * In vitro maturation * Protein Data Bank (PDB) ligand code for ivermectin * Innoson Vehicle Manufacturing Innoson Vehicle Manufacturing Co. Ltd. (commonly shortened to IVM) is a Nigerian automobile manufacturer headquartered in Nnewi, ...

at the Mees Observatory in Hawaii, SVM at Udaipur Solar Observatory, India, the SOLIS instrument at the

National Solar Observatory The National Solar Observatory (NSO) is a United States public research institute to advance the knowledge of the physics of the Sun. NSO studies the Sun both as an astronomical object and as the dominant external influence on Earth. NSO is headq ...

(strictly speaking, SOLIS is a scanned

spectropolarimeter Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves. Typically polarimetry is done on electromagnetic waves that have traveled through or ha ...

), and the narrowband filtergraph instrument on the Hinode spacecraft. Planned instruments include a vector polarimeter at the Advanced Technology Solar Telescope slated to be built in the 20-teens, and the HMI instrument aboard the

, launched in February 2010.

References

{{Cite journal , bibcode=2013SoPh..283..579L , title=The Hinode Spectro-Polarimeter , journal=Sol. Phys. , volume=283 , page=579, doi = 10.1007/s11207-012-0206-3 , doi-access=free

USO The United Service Organizations Inc. (USO) is an American nonprofit-charitable corporation that provides live entertainment, such as comedians, actors and musicians, social facilities, and other programs to members of the United States Armed F ...

Physical Research Laboratory, India *Home page for th
SOLIS
instrument, hosted by the

Astronomical imaging

References

External links