Glossary -- I

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ideal gas law

the equation of state for simple gases: pressure = (k × density × temperature)/(molecular weight of the gas).

inertia

the property of an object describing its tendency to stay at the same velocity (or at rest) unless a force acts on it.

inflation

a brief period of ultra-rapid expansion in the very early universe about 10>^-35 seconds after the Big Bang.

instrumentalism

a way of viewing scientific theories and models that says they are merely tools or calculation devices and are not to be interpreted as reality.

intensity

the number of waves or photons reaching your detector every second.

interferometer

an array of telescopes connected electronically to act as one large telescope with much improved resolution. The resolution of the interferometer is equal to a single telescope having a diameter equal to the length of the interferometer.

interstellar medium

the gas and dust between the stars.

inverse square law of light brightness

an object's apparent brightness decreases with the square of the distance. The apparent brightness is the amount of energy flowing through a given area in a given amount of time.

ion

a particle with an electrical charge (the number of electrons is different than the number of protons).

ion tail

(comet): one of the two tails of a comet made of ionized particles that points directly away from the Sun from the action of the solar wind. It has a bluish color from the emission lines mostly of ionized carbon monoxide.

irregular galaxy

a galaxy with no definite structure. Stars are distributed in bunches placed randomly throughout the galaxy. Many irregular galaxies have a lot of gas and dust still left in them from which stars are now forming.

isotope

a sub-group of an element in which the atomic nucleus has the same number of neutrons, as well as, the same number of protons. All of the atoms of an element will have very nearly the same chemical properties, but the isotopes can have very different nuclear properties.

isotropic

exhibiting the same property when looking in any given direction.

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last update: 06 August 1999