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Index (M)

MA - MC

MD - MF

MG - MJ

MK - MN

MO - MR

MS - MV

MW - MZ

Moment of truth
The fastest man-made object that ever leave the Earth is the Pinoeer 10 spacecraft, launched in 1972, and attained a speed of more than 32000 mph.


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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 700C to 1300C. The molten substance contains mostly silicates. When it is cooled and solidified it forms igneous rock on the surface of the Earth.

Magnadur Eng.
Tradename for a ceramic material made of sintered iron oxide and barium oxide. It is ferromagnetic and is mainly used for making permanent magnets.

magnetar Astron.
A subclass of neutron star that, like a pulsar, spins at a rate of several times persecond and produces X-ray flashes (in contrast, pulsars emit radio waves). Magnetar also occasionally releases a burst of gamma rays. Magnetars are thought to come from the death of very massive stars (about 30-40 solar masses) and only about less than a dozen of such neutron stars have been identified.

Magnetars have unusually large magnetic field that is thousands of times stronger than that of normal pulsars. Occasionally these stars can erupt and produce flares so strong that it can affect Earth's upper atmosphere even though the stars are thousands of light years away.

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

maltose Chem.
Also called malt sugar, it is a sugar consisting two linked glucose molecules that results from the action of the enzyme amylase on starch. Maltose occurs in barley seeds following germination and drying. This is the basis of malting process used in the manufacture of beer and malt whisky.

Maltose can be broken down in two glucose molecules via enzyme maltase. In the laboratory, this is achieved by heating with a strong acid for several minutes, a process called hydrolysis.

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.

massicot Min.
A natural mineral form of lead(II) oxide. See also litharge.

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