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Space and Solar Definitions - M

M - Mega, a multiplier, x106 (million) from the Greek "megas" (great). See the entry for CGPM.

M 3000 - The optimum high frequency radio wave with a 3000 km range, which reflects only once from the ionosphere (single hop transmission).

M100 - Messier Catalog entry number 100 is a spiral galaxy in the Virgo cluster seen face-on from our solar system.

Magflare - A geomagnetic and/or cosmic storm has been associated with this flare.

Magnetic Bay - A relatively smooth excursion of the h (horizontal) component (see geomagnetic elements) of the geomagnetic field away from and returning to quiet levels.

Magnetic Cloud - In general, any identifiable parcel of solar wind. More specifically, a region of about 0.25 au in radial dimension in which the magnetic field strength is high and the direction of one component of the magnetic field changes appreciably by means of a rotation nearly parallel to a plane. Magnetic clouds may be one manifestation of coronal mass ejections in the interplanetary medium.

Magnetic Local Time (Mlt) - On earth, analogous to geographic local time; mlt at a given location is determined by the angle subtended at the geomagnetic axis between the geomagnetic midnight meridian and the meridian that passes through the location. 15 degrees = 1 h. The geomagnetic meridian containing the sub-solar point defines geomagnetic local noon, and the opposite meridian defines geomagnetic midnight. (see geomagnetic field)

Magnetogram - Solar magnetograms are a graphic representation of solar mag- netic field strengths and polarity.

Magnetopause - The boundary layer between the solar wind and the magneto- sphere.

Magnetosphere - The magnetic cavity surrounding the earth, carved out of the passing solar wind by virtue of the geomagnetic field, which pre- vents, or at least impedes, the direct entry of the solar wind plasma into the cavity.

Major axis - The maximum diameter of an ellipse.

Majorflare - This flare is the basis for the forecast of geomagstorm, cosmic storm and/or protons in the earth's vicinity.

Mars - Fourth planet from the sun, a terrestrial planet.

Maser - A microwave traveling wave tube amplifier named for its process of Microwave Amplification by Stimulated Emission of Radiation. Compare with Laser. In the Deep Space Network, masers are used as low-noise amplifiers of downlink signals, and also as frequency standards.

MC-cubed - Mission Control and Computing Center at JPL (outdated).

MCCC - Mission Control and Computing Center at JPL (outdated).

MCD - DSN's maximum-likelyhood convolutional decoder, the Viterbi decoder.

MCT - Mission Control Team, JPL Section 368 mission execution real-time operations.

MDSCC - DSN's Madrid Deep Space Communications Complex in Spain.

Mean solar time - Time based on an average of the variations caused by Earth's non-circular orbit. The 24-hour day is based on mean solar time.

Medium Frequency. (Mf) - That portion of the radio frequency spectrum from 0.3 to 3 mhz.

Mercury - First planet from the sun, a terrestrial planet.

Meridians - Great circles that pass through both the north and south poles, also called lines of longitude.

MESUR - The Mars Environmental Survey project at JPL, the engineering prototype of which was originally called MESUR Pathfinder, later Mars Pathfinder.

Meteor - A meteoroid which is in the process of entering Earth's atmosphere. It is called a meteorite after landing.

Meteorite - Rocky or metallic material which has fallen to Earth or to another planet.

Meteoroid - Small bodies in orbit about the sun which are candidates for falling to Earth or to another planet.

Mev - Mega (million) electronvolt. A unit of energy used to describe the total energy carried by a particle or photon.

MGA - Medium-Gain Antenna onboard a spacecraft.

MGN - The Magellan spacecraft.

MHz - Megahertz (106 Hz).

Micrometer - µm, 10-6 meter.

Micron - Obsolete terms for micrometer, µm (10-6 m).

Microwave Burst - A radiowave signal associated with optical and/or x-ray flares.

Middle Latitudes - With specific reference to zones of geomagnetic activity, "middle latitudes" refers to 20 deg. To 50 deg. Geomagnetic.

Milky Way - The galaxy which includes the sun and Earth.

Millimeter - 10-3 meter.

MIT - Massachusetts Institute of Technology.

MLI - Multi-layer insulation (spacecraft blanketing).

mm - millimeter (10-3 m).

MO - The Mars Observer spacecraft.

Modulation - The process of modifying a radio frequency by shifting its phase, frequency, or amplitude to carry information.

MON - DSN Monitor System. Also, monitor data.

Moon - A small natural body which orbits a larger one. A natural satellite. Capitalized, the Earth's natural satellite.

MOSO - Multi-mission Operations Systems Office at JPL.

Mount Wilson Magnetic Classifications. Alpha - Denotes a unipolar sunspot group. Beta a sunspot group having both positive and negative magnetic polarities, with a simple and distinct division between the polarities. Beta-gamma a sunspot group that is bipolar but in which no continuous line can be drawn separating spots of opposite polarities. Delta a complex magnetic configuration of a solar sunspot group consisting of opposite polarity umbrae within the same penumbra. Gamma a complex active region in which the positive and negative polarities are so irregularly distributed as to prevent classification as a bipolar group.

MR - Mars relay.

Multiplexing - A scheme for delivering many different measurements in one data stream.

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