 galactic year

the unit of time in which the Solar System makes one revolution around the
Milky Way galaxy. The galactic year is estimated to be about 225 million
ordinary years. The age of the Solar System is about 20 galactic years.
 g

a symbol for the average acceleration produced by gravity at the Earth's
surface (sea level). The actual acceleration of gravity varies from place to
place, depending on latitude, altitude, and local geology. The symbol g is
often used informally as a unit of acceleration. standard acceleration of
gravity g is defined to be exactly 9.806
65 meters per second per second (m/s^{2}), or about 32.174 05 feet per
second per second.
 Ga

symbol for one billion (10^{9}) years. The a stands for the
Latin annus, year.
 galileo

the CGS unit of acceleration. One galileo is an acceleration of 1 centimeter
per second per second (cm/s^{2} ). One Gal is approximately 0.001 019 7 g.
The name of the unit honors the Italian astronomer and natural philosopher
Galileo Galilei (15641642), who proved that all objects at the Earth's surface
experience the same gravitational acceleration.
 gallon

a traditional unit of liquid volume, derived from the Roman galeta. A
U. S. gallon wine holds 4 liquid quarts or exactly 3.785 411 784 liters; a U.S.
gallon of water weighs about 8.33 pounds.
 garnets

a traditional unit of liquid volume in Russia. About 3.28 liters, 3.47
U.S. quarts or 2.89 British imperial quarts.
 generation

an informal unit of time. A generation is the average length of time
between the birth of a parent and the birth of the child. About 25 to 35 years.
 gig

an informal contraction of the gigabyte (GB) common in computer science,
as a unit of storage capacity.
 giga (G)

a metric prefix denoting 10^{9} or one billion. This prefix was coined
from the Greek word gigas , meaning giant.
 gigagram

an SI unit of mass equal to 10^{9} grams, one million kilograms, or 1
kilotonne (1000 metric tons).
 gigahertz (GHz)

a unit of frequency equal to 10^{9} per second, or 1 per nanosecond.
Cellular phones and microwave ovens operate with radio waves having frequencies
in the gigahertz range.
 gigajoule

a metric unit of energy commonly used in the energy industry. One gigajoule
equals 947 817 Btu, 277.7778 kilowatt hours, or about 9.48 therms.
 gigaliter

a metric unit of volume equal to 10^{9} liters or one million cubic
meters.
 gill

a traditional unit of volume for liquids, a gill is 1/4 pint. In the U. S.
customary system, one gill is equal to 1/2 cup, 4 fluid ounces, 7.21875 cubic
inches, or about 118.3 milliliters. In the British Imperial system, the gill
equals 5 fluid ounces, 8.670 cubic inches, or about 137.7 milliliters.
 gin

one of several spellings used in English for the jin, the Chinese weight unit
also called the catty.
 GMT

abbreviation for Greenwich Mean Time, the standard time of longitude 0°. This
meridian of longitude, called the prime meridian, was fixed as the
longitude of the Royal Greenwich Observatory in London by the International
Meridian Conference of 1884. GMT is five hours later than U.S. Eastern Standard
Time.
 go

a traditional Japanese unit of liquid volume. One go is about 180.39
milliliters, 0.3812 U.S. pint, or 0.3174 British imperial pint.
 googol

a unit of quantity equal to 10^{100} (1 followed by 100 zeroes). The
googol was invented by the American mathematician Edward Kasner (18781955) in
1938.
 grade

a unit of angle measurement equal to 1/400 circle, 0.01 right angle, 0.9°, or
54'.

a measure of the steepness of a slope, such as the slope of a road or a ramp.
 grade point

a unit of academic recognition used in U.S. schools and colleges. A student who
has a grade of A (4.0) on a course carrying 3 semester hours of credit receives
12 grade points.
 grain

a traditional unit of weight. 1/480 troy ounce, or exactly 64.798 91
milligrams. 5760 grains in a troy pound and 7000 grains in an avoirdupois
pound.

a unit of weight formerly used by jewelers in measuring diamonds and other
precious stones. The jeweler's grain is exactly 1/4 carat. Now that the carat
has been standardized at 200 milligrams, the jeweler's grain is exactly 50
milligrams, or approximately 0.7716 troy grain. This unit is widely used for
measuring pearls, so it is sometimes called the pearl grain.

a traditional French unit of weight equal to 53.115 milligrams.
 gram (g)

a unit of mass in the metric system. Name from the Greek gramma.One
gram is now defined to be 1/1000 of the mass of the standard kilogram, a
platinumiridium bar carefully guarded by the International Bureau of Weights
and Measures in Paris for more than a century. The gram is a small mass,
equal to about 15.432 grains or 0.035 273 966 ounce.
 gram equivalent

various names for the mass in grams of a substance that would react with or
replace one gram of hydrogen.
 gram weight or gram force

a unit of weight equal to the force exerted on a mass of one gram by gravity at
the Earth's surface: approximately 980.665 dynes, 9.806 65 millinewtons, or
about 0.002 2045 pounds of force in the English system.
 gran

a traditional German weight unit, varying in size but typically about 60
milligrams.
 grand

slang for 1000, the sum of 1000 dollars in the U.S., or 1000 pounds in Britain.
 grano

a traditional Italian weight unit, varying in size but typically about 50
milligrams. The plural is grani.
 Gregorian year

a unit of time equal to exactly 365.2425 days, the average length of a year in
the Gregorian calendar currently used throughout the world.
 grit

a measure of fineness for abrasive materials such as sandpaper, sanding belts,
or the finer materials used to polish optical surfaces.
 gross

a unit of quantity equal to a dozen dozen or 144. This commercial unit has been
in use since at least the 1400's.
