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Words begining with "M"


Region surrounding a celestial body where its magnetic field controls the motions of charged particles. The Earths magnetic field is dipolar in nature. That is, it behaves as if produced by a giant bar magnet located near the center of the planet with its north pole tilted several degrees from Earth's geographic north pole.

The Earth's magnetic field presents an obstacle to the solar wind, as a rock in a running stream of water. This obstacle is called a bow shock. The bow shock slows down, heats, and compresses the solar wind, which then flows around the rest of Earths magnetic field. See Van Allen belts.


Maryland Pilot Earth Science and Technology Education NETwork. NASA sponsored education project designed to complement NASAs Mission to Planet Earth. MAPS-NET has been developed to enrich math and science curricula and enhance teacher preparation in Earth system science.

Middle and high school teachers learn about Earth sciences and satellite direct readout at graduate-level summer workshops; academia, federal agencies, and the private sector form the support network.

MSFC (Marshall Space Flight Center)

See NASA Centers.

Mean Anomaly (aka MO or MA or phase)

Specifies the mean location (true anomaly specifies the exact location) of a satellite on an orbit ellipse at a particular time, assuming a constant mean motion throughout the orbit . Epoch specifies the particular time at which the satellites position is defined, while mean anomaly specifies the location of the satellite at epoch. Mean anomaly is measured from 0 degrees to 360 degrees during one revolution. It is defined as 0 degrees at perigee, and hence is 180 degrees at apogee. See Keplerian elements.

Mean Motion (aka NO)

Averaged speed of a satellite in a non-circular orbit (i.e. eccentricity>0). Satellites in circular orbits travel at a constant speed. Satellites in non-circular orbits move faster when closer to the Earth, and slower when farther away. Common practice is to compute the mean motion (average the speed), which is measured in revolutions per day.

Measurement System Integrity

The tracking and documentation over the long term of all causes of error or uncertainty in a final data-analysis product. These include instrument calibration, adequacy of measurement validation, data coverage and sampling density, availability and quality of ancillary data, procedures for data analysis and reduction, the results of checks against independent measurement, and quantitative error analysis.

Measurement Validation

The establishment of confidence in the numerical relationship between the calibrated sensor output and the actual variable being measured.

Mercator Projection

A method of making maps in which the Earths surface is shown as a rectangle with the meridians as parallel straight lines spaced at equal intervals and the parallels of latitude as parallel straight lines intersecting the meridians at right angles. Areas away from the equator appear larger than they are, with the qreatest distortion near the poles.


The upper boundary of the mesosphere where the temperature of the atmosphere reaches its lowest point


The atmospheric layer above the stratosphere, extending from about 50 to 85 kilometers altitude. The temperature generally decreases with altitude.


Information describing the content or utility of a data set. For example, the dates on which data were procured are metadata.


The former Soviet Union's series of polar-orbiting weather satellites. The Meteor satellites transmit images in a system compatible with the NOAA polar-orbitinq satellites.


Study of the atmosphere and its phenomena.


METEOrological SATellite. Europe's geostationary weather satellite, launched by the European Space Agency and now operated by an organization called Eumetsat. METEOSAT transmits at 1691 and 1694.5 MHz.


Generic term for meteorological ( weather satellites).

MHz (megahertz)

1,000,000 hertz.

Micrometer (um, aka micron)

One millionth of a meter, used to measure wavelengths in the electromagnetic spectrum.


Controlling unit of a microcomputer, laid out on a tiny silicon chip and containing the logical elements for handling data, performing calculations, carrying out stored instructions, etc.


Electromagnetic radiation with wavelengths between about 1000 micrometers and one meter

Middle Infrared

Electromagnetic radiation between the near infrared and the thermal infrared, about 2-5 micrometers.

Millibar (mb)

One thousandth of a bar, a unit of atmospheric pressure. The average atmospheric pressure at sea level is ) .01325 bars or 1013.25 mb. See pascal (Pa).

Mission to Planet Earth (MTPE)

International research program to understand our planet's environment as a system. A major challenge of MTPE is to observe, understand, model, assess, and eventually predict global change. Meeting this challenge will help to evaluate the impact that human activity (e.g., clearing forests and burning fossil fuels) has on our environment, and to distinguish human-induced changes from the effects of natural events (e.g. volcanic eruptions, erosion).

NASA's MTPE uses space-, aircraft-, and ground-based measurements to provide the scientific basis for understanding global change. The program will produce longterm global maps of clouds, land and ocean vegetation, atmospheric ozone, sea-surface temperature, and other global processes necessary to understand the state of the Earth and to detect any patterns of change. This information will be available to scientists and policy makers through the Earth Observing System Data and Information System (EOSDIS).

The centerpiece of NASA's MTPE will be the Earth Observing System (EOS), a series of satellites planned for launch beginning in 1998. Measurements from EOS will be complemented by the Earth Probes, a series of discipline-specific satellites and instruments designed to observe Earth processes where smaller platforms and/or different orbits from EOS are required. Planned Earth Probes will measure tropical rainfall, ocean productivity, ozone, and ocean surface winds. In addition, MTPE includes current NASA Earth science missions collecting important data on the global environment, such as the Upper Atmosphere Research Satellite ( UARS) and the Ocean Topography Experiment ( TOPEX/POSEIDON), Space Shuttle experiments such as ATLAS, and aircraft campaiqns.

Model (noun)

A mathematical representation of a process, system, or object developed to understand its behavior or to make predictions. The representation always involves certain simplifications and assumptions.

Modem (modulator/demodulator)

Device that allows two computers (which use binary data in the form of bits) to communicate using a telephone line (which uses tones). When the computer is transmitting data, the modem is needed to modulate binary data into tones. When receiving data, the device is needed to demodulate the tones to obtain the binary data required by the computer. Since the computer must be both a transmitter and receiver of data, the modem must be able to modulate and demodulate data.


Variation in the frequency of a radio wave in accordance with some other impulse. Modulation is essential to communication systems in which a number of different signals must all share the same medium. One way this sharing can be accomplished is to place each signal in its own band of frequencies in the medium. Amplitude modulation and frequency modulation are two ways in which signals can be moved within the frequency domain to accomplish placement and sharing.

The combining of a number of signals to share a communication medium by dividing it into different frequency bands for each signal is called frequency-division multiplexing.

Amplitude modulation (AM) is technologically quite simple, and the bandwidth of the amplitude-modulated carrier is at most twice the bandwidth of the modulating signal. However, an amplitude-modulated carrier is very prone to the effects of additive noise.

Frequency modulation (FM) is more complicated than amplitude modulation, and the bandwidth of the frequency-modulated carrier can be many times that of the modulating signal. However, the process of demodulating a frequency-modulated carrier eliminates much of the deleterious effects of additive noise. This trade-off between bandwidth and noise reduction characterizes most communication situations.


Heavy winds characterized by a pronounced seasonal change in direction. Winds usually blow from land to sea in the winter, while in the summer, the flow reverses and precipitation is more common. Monsoons are most typical in India and southern Asia.

Montreal Protocol

An international agreement to drastically reduce CFC production, the Protocol was adopted in Montreal in 1987. It was significantly strengthened at a subsequent meeting in London in 1990 that called for a complete elimination of CFCs by the year 2000. The agreement was again amended by a Meeting of the Parties in Copenhagen in November 1992. Consumption of controlled substances - such as CFCs and halons - was greatly reduced or eliminated, and many accountability dates were moved forward. often from January 2000 to 1 January 1996


A composite picture built up from a number of image segments. An example of a mosaic is the WEFAX transmission, which includes both polar and mercator mosaics derived from TIROS-N/NOAA polar orbit image data.

Mountain and Valley Breezes

System of winds that blow downhill during the night (mountain breeze) and uphill during the day (valley breeze).


See Mission to Planet Earth


A device that combines several separate communications signals into one and outputs them on a sinqle line.

Multispectral Scanner (MSS)

A line-scanning instrument flown on Landsat satellites that continually scans the Earth in a 185 km (100 nautical miles) swath. On Landsats 1, 2,4, and 5, the MSS had four spectral bands in the visible and near-infrared with an IFOV of 80 meters. Landsat-3 had a fifth band in the thermal infrared with an IFOV of 240 meters.


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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: May 13 2021

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