Glossary -- N

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nanometer

a very tiny distance equal to one-billionth of a meter (0.000000001 meter).

natural selection

the primary mechanism of evolution by which, over time, heritable traits that enhance survival and successful reproduction will become progressively more common in succeeding generations in any local environment. It is a NON-random process that produces adaptations.

neap tide

tide that has a small change between low and high tide. It occurs at first and third quarter phase, when the Moon's tidal effect is perpendicular with the Sun's tidal effect.

neutrino

a sub-atomic particle with very small mass that is produced in nuclear fusion reactions and rarely interacts with ordinary matter. Neutrinos travel at the nearly the speed of light and provide current information about the number of nuclear fusion reactions occurring in a star's core (in the case of the Sun, the information is only about 8.3 minutes old).

neutron

subatomic particle with zero charge (neutral charge) that is found in the nucleus of an atom. It is slightly more massive than the positively-charged proton.

neutron degeneracy pressure

pressure exerted by a degenerate gas made of neutrons. It is what prevents further collapse of a neutron star.

neutron star

the collapsed core for an intermediate to high-mass star. The core is more than 1.4 solar masses but less than 3 solar masses and is about the diameter of a city. The pressure from degenerate neutrons prevents further collapse.

newton

unit of force in the metric system. It is used to specify the amount of weight.

Newton's 1st law

(of motion): a body at rest remains at rest, and one moving in a straight line maintains a constant speed and same direction unless it is deflected by a force.

Newton's 2nd law

(of motion): the amount of force needed to cause an acceleration depends on an object's mass, such that the force applied = the mass of an object × its acceleration.

Newton's 3rd law

(of motion): for every action force ON an object, there is an equal but opposite force BY the object.

north celestial pole

(NCP): projection of the Earth's north pole onto the sky. The NCP altitude = the observer's northern latitude.

nova

an object that greatly increases in brightness rapidly, so it appears as a ``new star''. It is caused by the buildup on a white dwarf's surface of hydrogen gas from a companion star to the point where the hydrogen fuses explosively into helium. The super-rapid fusion does not blow up the white dwarf, so the process can repeat itself (contrast with a Type I supernova).

nuclear fusion

the process used by stars to generate energy: less-massive nuclei are fused together under extremely high temperatures and densities to form more-massive nuclei plus some energy. The energy comes from the transformation of some of the mass into energy.

nucleus

(comet): the ``dirty iceberg'' about the size of a city from which all of the stuff in a comet comes from. Irregularly-shaped it is made of dust and frozen gases.

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last updated: 27 May 2001