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Index (M)
MA - MC
MD - MF
MG - MJ
MK - MN
MO - MR
MS - MV
MW - MZ
Moment of truth
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The Voyager I spacecraft is the most distant man-made object in the universe. It was launched in 1977 and as in 2002, it was more than 8 billions miles from the Earth. |
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MA - MC
MACHO Astron.
The acronym for Massive Astronomical Compact Halo Object. Is is a celestial object that possibly exists at the outer edge (or halo) of the galaxy that
is too faint to be observed directly. Possible candidates for MACHOs are brown dwarfs (failed stars), planets (from other stars), black holes and asteroids.
MACHOs are considered as one of the possible group of objects that account for the missing matter (the dark matter) in the Universe. A MACHO may possibly
be detected especially when it passes in front of a distance star. If its mass is large enough, it causes distortion of the light from the star, an effect called the gravitational lensing, and the mass
of the MACHO causing this phenomenon can be measured.
macromolecules Chem.
A very large molecule which can be either natural or synthetic. For instance, synthetic polymers which have a large number repeat units are macromolecules. Natural biological molecules
such as proteins, which consist of a large number of amino acid residues, are also macromolecules.
magma Geol.
Molten rock below the surface of the Earth (Earth's crust). The temperature of the molten rock can be in the range of 700°C to 1300°C. The molten substance contains mostly silicates. When it is
cooled and solidified it forms igneous rock on the surface of the Earth.
magnetosphere Astron.
A zone of charged particles trapped by a planet's or star's magnetic field, lying above the atmosphere and extends far into space. It can be regarded as the region of space in which a planet's
magnetic field dominates that of solar wind.
magnitude Astron.
The method used to compare the apparent brightness of stars and other celestial objects. It was first conceived by Hipparchus in second century BC. In 140 AD, Ptolemy refined the method and used 1 to 6 to compare star brightness.
The brightness decreases (becomes fainter) as the number increases and the 1st magnitude is 100 times brighter than the 6th magnitude stars. In other words, the difference of one magnitude corresponds to a brightness difference of about 2.5.
Table below lists magnitudes of some selected objects.
Object |
Apparent magnitude |
Sun |
-26.7 |
Full Moon |
-12.5 |
Sirius (brightest star) |
-1.5 |
Betelgeuse |
0.8 |
Naked eye limit |
6.0 |
manganin Eng.
A copper alloy containing 12-18% manganese and 1-4% nickel. For example, manganin alloy 130 with 84% copper, 12% manganese and 4% nickel. These alloys have high electrical resistance that is insensitive to
temperature changes but is very sensitive to pressure . It is used to make resistance wires and pressure gages.
marsh gas Chem.
A gas, usually mixture of methane and carbon dioxide, that is produced by rotting plants in marshes, a wetland covered with grasses and low plants.
MA - MC
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
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