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This page is meant to make it easier for you to understand the content of this web site. The glossary contains both astronomical and art terms.
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Parallax: The shift a star appears to make when viewed from two different locations. The closer the object the larger shift. This is a method which has a lesser accuracy the further away the object is.
Parsec: A distance scale, 3.26 light years, or about 30 trillion kilometres.
Periastron: A point in an orbit in which the object is closest to its' main star.
Perigee: The point in the moon's orbit around earth on which it is closest.
Perihelion: The point in an object's orbit around the sun on which it is closest.
Period-Luminosity Relation: A relationship between the pulsation period of a variable star and its luminosity. Generally the more luminous the star the longer the pulsation period. The relationship permits distances to be measured.
Pesek, Ludek (1919-1999): Illustrator and fine artist. His work became known to the american audiance through the National Geographic Magazine. More. Ludek Pesek gallery.
Photon: A photon is a light wave/particle, whether be it is a radio wave or a gamma ray. Link: Photons and radiation.
Planet: A large object which does not produce its own energy and does orbit a star. The difference between a planet or an asteroid is sometimes vague. How large does an object have to be, to be called a planet?
Planetary nebula: A kind of a nebula that is created when a star throws off a huge amounts of gas. The sun is believed to create one when it will near the end of its life. Nebulae give birth to new stars. Link: Planetary nebulae.
Population I stars: Relatively young stars, containing a larger fraction of metals, found mainly in the disk of the Galaxy.
Population II stars: Relatively old stars, containing a smaller fraction of metals, found mainly in the halo of the Galaxy and in Globular Clusters.
Proton: The second part of an atomic nuclei. It is positively electrically charged. The other part is a neutron, which is neutral in charge.
Proton-proton chain: The fusion reaction of four protons which become a helium atum with two protons and two neutrons, and a very energetic light wave, a photon. A neutrino is also produced in this chain. Link: Fusion processes and radiation.
Protoplanet: This is an early stage of a planet's formation. It is a clump of material which may gather more material to make a planet.
Protostar: A clump of gas which may become a star if it has enough mass. When the gravitational pressure which points inwards is balanced by an equal internal gas pressure, pointing in the opposite direction is achieved a star is born. Not all protostars become real stars.
Pulsar: A rotating magnetized neutron star that produces regular pulses of radiation when observed from a distance. A pulse is produced every time the rotation brings the magnetic pole region of the neutron star into view. In this way the pulsar acts much as a light house does, sweeping a beam of radiation through space.
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