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Moment of truth
The fastest man-made object that ever leave the Earth is the New Horizon spacecraft, launched in January 2006, and attained a speed of more than 36000 mph.

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galena Min.
galena mineral A mineral form of lead(II) sulfide, grey metallic with bluish tint and with a characteristic cubic crystal structure. It is the chief ore of lead with important deposits found at Broken Hill, Australia, USA (Missouri, Kansas), Germany, UK and Zambia. Sometimes the mineral contains up to 1% of silver. For this reason, silver is also produced as a by product. Galena can also contain copper, arsenic, zinc and antimony.

gamma-ray burst Astron.
An outburst (lasts for a few seconds to a few minutes) of gamma-ray that may outshine the entire Universe in gamma rays. This enormous amount of energy usually originates near the edge of the Universe, at around 10 billion light years. Since its discovery in 1960s, astronomers have been trying to identify the reason and source of such bursts. Recently, a powerful 30-second burst (designated GRB 030329) was detected at a relatively near distance of 2 billion light years, in 29 March 2003. The burst was found to relate to a supernova (designated 2003dh), and the latter was seen to brighten few days later, on 8 April 2003.

gas molar volume Chem.
The volume occupied by 1 mole of any gas. It measures 22.4 dm3 at the standard temperature (0C) and pressure (one atmospheric pressure); 24.0 dm3 at room temperature (20C) and pressure (one atmospheric pressure).

gauge bosons Phys.
Imaginary particles acting as 'force carriers' that mediate the interactions between two fundamental particles. It is also known as field particles. For example, photons for electromagnetic interactions.

gauge pressure Chem., Phys.
Pressure measured on a guage instrument that reads zero at atmospheric pressure. See also absolute pressure.

gauge theory Phys., Math.
A class of physical theories or mathematical formulation of the interactions, derived from a symmetry principles. The basic assumption is that the equations are invariant under certain transformations of the wave function. Quantum chromodynamics and electroweak theory, which are the theories that deal with strong and weak interactions, are examples of gauge theory. The theory also stipulates that localized symmetry transformation of space-time can be carried out without affecting what happens in another region.

gaylussite Min.
A mineral consisting of a mixed hydrated sodium and calcium carbonate, Na2CO3.CaCO3.5H2O. It is a monoclinic crystal mineral, colorless but sometimes appear yellowish white. The mineral can become cloudy due to dehydration and usually associate other minerals such as trona and halite. It is named after the French chemist Joseph L. Gay-Lussac (1778-1850).

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