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Magnetometer
A magnetometer, also known as a gaussmeter or teslameter, is an instrument that measures the strength and direction of magnetic fields, from inexpensive Hall-effect chips to highly sensitive SQUIDs.
Magnetometry
Magnetometry is the measurement of magnetic fields or of the magnetization of materials, using instruments from Hall sensors and fluxgates to SQUIDs and atomic magnetometers, dating to the 1830s.
Magnetomotive force
Magnetomotive force (MMF), also called magnetomotance, is the quantity that drives magnetic flux around a magnetic circuit, equal to a coil's turns times its current and measured in ampere-turns.
Magnetopause
The magnetopause is the boundary of a planet's magnetosphere, where its magnetic field balances the solar wind; at Earth it lies about 10 Earth radii sunward.
Magnetophoresis
Magnetophoresis is the motion of magnetically susceptible particles through a viscous medium under a magnetic field gradient, used to separate, collect, or analyze particles and labeled cells.
Magnetoresistance
Magnetoresistance is the change of a material's electrical resistance under a magnetic field, first reported by William Thomson in 1857 and used in hard drive read heads, sensors, and MRAM.
Magnetoresistive sensor
A magnetoresistive sensor is a solid-state device that measures magnetic fields through a field-dependent resistance change, based on AMR, GMR, or TMR effects in ferromagnetic thin films.
Magnetorheological fluid
A magnetorheological fluid is a smart material of micron-sized magnetic particles in a carrier oil that stiffens reversibly in a magnetic field; applications include the MagneRide vehicle suspension.
Magnetorotational instability
The magnetorotational instability (MRI) is a magnetohydrodynamic instability of conducting disks whose angular velocity decreases outward, first applied to accretion disks by Balbus and Hawley in 1991.
Magnetosheath
The magnetosheath is the region of shocked, compressed solar wind between a planet's bow shock and magnetopause, a turbulent natural laboratory studied by spacecraft such as MMS and Cluster.
Magnetosonic wave
A magnetosonic wave, also called a magnetoacoustic wave, is a compressional magnetohydrodynamic wave in a magnetized plasma, coupling plasma pressure disturbances to magnetic field disturbances.
Magnetosphere
A magnetosphere is the region of space around a planet or moon controlled by its magnetic field, deflecting the solar wind; Earth's shields its atmosphere and drives auroras.
Magnetosphere of Uranus
The magnetosphere of Uranus, discovered by Voyager 2 in January 1986, is unusually tilted and offset, so its geometry changes dramatically over the planet's 17-hour day.
Magnetospheric accretion
Magnetospheric accretion is the process by which a magnetized young star truncates its accretion disk and channels gas along field lines to its magnetic poles.
Magnetospheric convection
Magnetospheric convection is the large-scale circulation of plasma and magnetic flux through Earth's magnetosphere, driven by interaction between the solar wind and Earth's magnetic field.
Magnetospheric Multiscale Mission
The Magnetospheric Multiscale Mission is a NASA mission, launched in 2015, that flies four identical spacecraft in tetrahedral formation through Earth's magnetosphere to study magnetic reconnection.
Magnetospheric origin of fast radio bursts
The magnetospheric origin of fast radio bursts is the hypothesis that these millisecond radio bursts are emitted inside the magnetospheres of compact objects, chiefly magnetars.
Magnetospheric substorm
A magnetospheric substorm is a rapid release of energy stored in Earth's magnetotail, lasting about an hour, marked by sudden auroral brightening and capable of damaging satellites.
Magnetostatics
Magnetostatics is the branch of electromagnetism describing magnetic fields from steady currents and permanent magnets, applied in MRI magnet design, magnetic shielding, and electric motors.
Magnetostratigraphy
Magnetostratigraphy is a stratigraphic technique that dates and correlates rocks by matching their record of magnetic polarity reversals against the geomagnetic polarity time scale, providing time lines where direct dating is not possible.
Magnetostriction
Magnetostriction is the change in shape or dimensions of a ferromagnetic material when magnetized, first observed by James Joule in 1842 and used in actuators and sensors.
Magnetotail
The magnetotail is the long, stretched nightside portion of Earth's magnetosphere, extending at least 220 Earth radii downstream, where geomagnetic substorms begin and the polar aurora originates.
Magnetotellurics
Magnetotellurics is a passive geophysical method that uses natural electric and magnetic field variations to image subsurface electrical conductivity from hundreds of meters to hundreds of kilometers deep.
Magnification
Magnification is the factor by which an optical system enlarges an object's appearance, defined as image height over object height for lenses, or angular magnification for microscopes and telescopes.
Magnification bias
Magnification bias is the change in the detection rate of background sources in flux-limited surveys caused by gravitational lensing, which brightens sources and magnifies the sky area.
Magnitude (astronomy)
Magnitude, also called star magnitude, is astronomy's logarithmic measure of celestial brightness: five magnitudes equal a 100-fold brightness difference, so brighter objects carry smaller or negative numbers.
Magnitude (mathematics)
Magnitude in mathematics is the property that determines whether an object is larger or smaller than others of the same kind, from Euclid's geometry to vector norms.
Magnitude of completeness
The magnitude of completeness (Mc) is the lowest magnitude at which 100% of earthquakes in a region are reliably detected by a seismic network; below it, smaller quakes are missed.
Magnolol
Magnolol is a dimeric phenolic neolignan (C18H18O2) and a primary active component of Magnolia officinalis bark, used in Chinese and Japanese herbal medicine and studied for anti-inflammatory, antitumor, and neuroprotective effects.
Magnon
A magnon is the quantum of a spin wave, the collective wavelike disturbance of aligned spins in a magnetically ordered solid; carrying spin but no electric charge, it underlies magnonics.