Aeronautics and Space Report of the President FY 1995 Activities



m Meter

M Mach number-a relative number named after Austrian physicist Ernst Mach (1838-1916) and indicating speed with respect to that of sound in a given medium; in dry air at 32 degrees Fahrenheit and at sea level, for example, Mach 1=approximately 741 mph or 1,192 kilometers per hour

Mach See M

Magellanic Stream A large filament of neutral hydrogen gas from the Milky Way's radio emission that originates at the Small Magellanic Cloud, a Milky Way satellite dwarf galaxy, and extends almost one-third of the way around the sky

magnetosphere The region of the Earth's atmosphere where ionized gas plays an important role in the atmospheric dynamics and where consequently, the geomagnetic field also exerts an important influence; other magnetic planets, such as Jupiter, have magnetospheres that are similar in many respects to the Earth's

maser Microwave Amplification by Simulated Emission of Radiation-a device introduced in 1953 with multiple applications in physics, chemistry, and radio and television communication

mesopause The layer of the Earth's atmosphere with the lowest temperature, from 50 to 53 miles (80 to 85 kilometers) up

mesosphere That portion of the Earth's atmosphere located 34 to 50 miles (55 to 80 kilometers) up, where temperature decreases with increasing altitude

METEOR Multiple Experiment to Earth Orbit and Return (program)

MinSci (Russian) Ministry of Science and Technology Policy

MMU Manned Maneuvering Unit

Mode C transponder A radar beacon receiver/transponder capable of reporting the attitude of the aircraft aboard which it is installed

MOU Memorandum of Understanding

MSS Multispectral Scanner

MTCR Missile Technology Control Regime

MTPE Mission to Planet Earth-a program developed by NASA and the world scientific community to provide scientists with data that will allow them to understand the planet as a total system and to measure the effects of the human population on it

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Curator: Lillian Gipson
Last Updated: September 5, 1996
For more information contact Steve Garber, NASA History Office,