Index

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

 

P

Paleozoic
A geological term denoting the time in Earth history between 570 and 245 million years ago.
Pahoehoe
A type of basalt lava flow characterized by a smooth glassy skin, and constructed of innumerable "flow units" called "toes"; pahoehoe flows advance at rates of 1 to 10 meters (3 to 33 feet) hour and are associated with low-effusion-rate eruptions with little to no fountaining.
Palimpsest
A circular feature on the surface of dark icy moons such as Ganymede and Callisto lacking the relief associated with craters; Pamlimpsests are thought to be impact craters where the topographic relief of the crater has been eliminated by slow adjustment of the icy surface.
Palus
A swamp.
Patera
Shallow crater; scalloped, complex edge.
Peak Ring
A central uplift characterized by a ring of peaks rather than a single peak; peak rings are typical of larger terrestrial craters above about 50 kilometres (30 miles) in diameter.
Penumbra
The outer filamentary region of a sunspot.
Periapsis
The point in the orbit closest to the planet.
Perigee
The point in the orbit closest to the Earth.
Perihelion
The point in its orbit where a planet is closest to the Sun.
Proton
A proton is a subatomic particle found in the nucleus of every atom.  The particle has a positive electrical charge, equal and opposite to that of the electron.   If isolated, a single proton would have a mass of only 1.673 ? 10-27 kilogram, just slightly less than the mass of a neutron.
The number of protons in an element's nucleus is called the atomic number.  This number gives each element its unique identity.  In the atoms of any particular element, the number of protons in the nuclei is always the same.  An atom of simple hydrogen has a nucleus consisting of a single proton all by itself.  The nuclei of all other elements nearly always contain neutrons in addition to protons.
Protons need not be confined to the nuclei of atoms.  When protons are found outside atomic nuclei, they acquire fascinating, bizarre, and potentially dangerous properties, similar to those of neutrons in similar circumstances.  But protons have an additional property. Because they carry an electric charge, they can be accelerated by electric and/or magnetic fields.  High-speed protons, and atomic nuclei containing them, are emitted in large numbers during solar flares.  The particles are accelerated by the earth's magnetic field, causing ionospheric disturbances known as geomagnetic storms.
Perturb
To cause a planet or satellite to deviate from a theoretically regular orbital motion.
Photosphere
The visible surface of the Sun; the upper surface of a convecting layer of gases in the outer portion of the sun whose temperature causes it to radiate light at visible wavelengths; sunspots and faculae are observed in the photosphere.
Phreatic Eruption
A volcanic eruption or explosion of steam, mud or other material that is not incandescent; this form of eruption is caused by the heating and consequent expansion of ground water due to an adjacent igneous heat source.
Plage
Bright regions seen in the solar chromosphere.
Planar Features
Microscopic features in grains of quartz or feldspar consisting of very narrow planes of glassy material arranged in parallel sets that have distinct orientations with respect to the grain's crystal structure.
Planitia
Broad plains that occupy lowlands on planetary surfaces.
Planum
A plateau or high plain.
Plasma
A low density gas in which the individual atoms are charged, even though the total number of positive and negative charges is equal, maintaining an overall electrical neutrality.
Polarization
A special property of light; light has three properties, brightness, colour and polarization.
Porthole
A dimensional doorway between time and space.
Prana Energy
A source of liquid gold energy in the physical body at the centre of a major charka.
Precambrian
A geological term denoting the time in Earth history prior to 570 million years ago.
Pressure Ridge
A ridge formed by the uplift of a lava flow crust due to pressure of the flowing lava.
Prominence
An eruption of hot gases above the photosphere of the Sun. Prominences are most easily visible close to the limb of the Sun, but some are also visible as bright streamers on the photosphere.
Promontorium
A cape.
Protection Shield
A technique used to protect both the visual and physical body from harm.
Pseudo Crater
A generally circular crater produced by a phreatic eruption resulting from emplacement of a lava flow over wet ground.
Pyroclastic
Pertaining to clastic (broken and fragmented) rock material formed by volcanic explosion or aerial expulsion from a volcanic vent.
Pumice
A light vesicular form of volcanic glass with a high silica content; it is usually light in colour and will float on water.

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