Vector magnetograph
Encyclopedia
A vector magnetograph is a type of imaging telescope
that can estimate the 3-D
vector of the magnetic field
on a distant body with a resolved line spectrum. Magnetographs are useful for studying the Sun
because the surface magnetic field is important to the creation and maintenance of the solar corona, and gives rise to the phenomena of solar flare
s 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 that affects the wavelength
of emission and/or absorption spectral line
s in the presence of a magnetic field. The Zeeman splitting is caused by the fact that individual atom
s are magnetized due to the circulating motion of electron
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 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 spectral line
, for example the 525.02 nm 'Fe I' line from neutral (non-ionized) iron
. The measured shifts in wavelength are fractions of a picometre
. Measuring the full spectral profile of the line with this precision requires a high-dispersion spectrograph and a long time to collect sufficient photon
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 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
s of the spectral line, and operate much more quickly: the HMI
instrument on board the Solar Dynamics Observatory
will produce a vector magnetogram every few minutes.
The splitting effect is antisymmetric
along the line-of-sight, but 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 IVM at the Mees Observatory in Hawaii, SVM
at Udaipur Solar Observatory, India, the SOLIS
instrument at the National Solar Observatory
(strictly speaking, SOLIS is a scanned spectropolarimeter), 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 Solar Dynamics Observatory
, launched in February 2010.
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
that can estimate the 3-D
Three-dimensional space
Three-dimensional space is a geometric 3-parameters model of the physical universe in which we live. These three dimensions are commonly called length, width, and depth , although any three directions can be chosen, provided that they do not lie in the same plane.In physics and mathematics, a...
vector of the magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
on a distant body with a resolved line spectrum. Magnetographs are useful for studying the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
because the surface magnetic field is important to the creation and maintenance of the solar corona, and gives rise to the phenomena of solar flare
Solar flare
A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...
s and space weather
Space weather
Space weather is the concept of changing environmental conditions in near-Earth space or thespace from the Sun's atmosphere to the Earth's atmosphere. It is distinct from the concept ofweather within the Earth's planetary atmosphere...
.
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 that affects the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of emission and/or absorption spectral line
Spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...
s in the presence of a magnetic field. The Zeeman splitting is caused by the fact that individual atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s are magnetized due to the circulating motion of electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
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 wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
, 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 spectral line
Spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...
, for example the 525.02 nm 'Fe I' line from neutral (non-ionized) iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
. The measured shifts in wavelength are fractions of a picometre
Picometre
A picometre is a unit of length in the metric system, equal to one trillionth, i.e. of a metre, which is the current SI base unit of length...
. Measuring the full spectral profile of the line with this precision requires a high-dispersion spectrograph and a long time to collect sufficient photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s to make the measurement with precision. For example, SOLIS
Solis
- People :* Brian Solis, American marketing executive* Fermín Solís, Spanish cartoonist* Gabrielle Solis, a fictional character on the ABC drama Desperate Housewives* Hilda Solis, current U.S...
requires about an hour to gather polarized spectral profiles over the whole Sun, and Hinode
Hinode
Hinode , formerly Solar-B, is a Japan Aerospace Exploration Agency Solar mission with United States and United Kingdom collaboration. It is the follow-up to the Yohkoh mission and it was launched on the final flight of the M-V-7 rocket from Uchinoura Space Center, Japan on 22 September 2006 at...
, the recently launched spacecraft with a 0.5-meter 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 (mathematics)
In mathematics, a moment is, loosely speaking, a quantitative measure of the shape of a set of points. The "second moment", for example, is widely used and measures the "width" of a set of points in one dimension or in higher dimensions measures the shape of a cloud of points as it could be fit by...
s of the spectral line, and operate much more quickly: the HMI
HMI
HMI can refer to:* Hahn-Meitner-Institut, a research institut in Berlin, Germany, now called Helmholtz-Zentrum Berlin* Hammond–Whiting , an Amtrak station in Indiana, United States, with the code HMI....
instrument on board the Solar Dynamics Observatory
Solar Dynamics Observatory
The Solar Dynamics Observatory is a NASA mission which will observe the Sun for over five years. Launched on February 11, 2010, the observatory is part of the Living With a Star program...
will produce a vector magnetogram every few minutes.
The splitting effect is antisymmetric
Antisymmetric
The word antisymmetric refers to a change to an opposite quantity when another quantity is symmetrically changed. This concept is related to that of Symmetry and Asymmetry. The difference between these three concepts can be simply illustrated with Latin letters. The character "A" is symmetric about...
along the line-of-sight, but 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 IVM at the Mees Observatory in Hawaii, SVM
SVM
SVM can refer to:* SVM * Saskatchewan Volunteer Medal* Scanning voltage microscopy* Schuylkill Valley Metro* Secure Virtual Machine, or AMD Virtualization , a virtualization technology by AMD* Solaris Volume Manager...
at Udaipur Solar Observatory, India, the SOLIS
Solis
- People :* Brian Solis, American marketing executive* Fermín Solís, Spanish cartoonist* Gabrielle Solis, a fictional character on the ABC drama Desperate Housewives* Hilda Solis, current U.S...
instrument at the National Solar Observatory
National Solar Observatory
The mission of the National Solar Observatory is to advance knowledge of the Sun, both as an astronomical object and as the dominant external influence on Earth, by providing forefront observational opportunities to the research community...
(strictly speaking, SOLIS is a scanned spectropolarimeter), and the narrowband filtergraph instrument on the Hinode
Hinode
Hinode , formerly Solar-B, is a Japan Aerospace Exploration Agency Solar mission with United States and United Kingdom collaboration. It is the follow-up to the Yohkoh mission and it was launched on the final flight of the M-V-7 rocket from Uchinoura Space Center, Japan on 22 September 2006 at...
spacecraft. Planned instruments include a vector polarimeter at the Advanced Technology Solar Telescope
Advanced Technology Solar Telescope
The Advanced Technology Solar Telescope is a large domed solar telescope facility that is planned to be built by the National Solar Observatory atop the Haleakala volcano on the Pacific island of Maui. The site was selected for its clear daytime atmospheric seeing conditions, which will enable...
slated to be built in the 20-teens, and the HMI
HMI
HMI can refer to:* Hahn-Meitner-Institut, a research institut in Berlin, Germany, now called Helmholtz-Zentrum Berlin* Hammond–Whiting , an Amtrak station in Indiana, United States, with the code HMI....
instrument aboard the Solar Dynamics Observatory
Solar Dynamics Observatory
The Solar Dynamics Observatory is a NASA mission which will observe the Sun for over five years. Launched on February 11, 2010, the observatory is part of the Living With a Star program...
, launched in February 2010.
External links
- Vector Magnetograph description by NASANASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
Marshall Space Flight CenterMarshall Space Flight CenterThe George C. Marshall Space Flight Center is the U.S. government's civilian rocketry and spacecraft propulsion research center. The largest center of NASA, MSFC's first mission was developing the Saturn launch vehicles for the Apollo moon program... - Solar Vector Magnetograph description by USO Physical Research Laboratory, India
- Home page for the SOLIS instrument, hosted by the National Solar ObservatoryNational Solar ObservatoryThe mission of the National Solar Observatory is to advance knowledge of the Sun, both as an astronomical object and as the dominant external influence on Earth, by providing forefront observational opportunities to the research community...