Astroparticle Physics

16 Glossary 325See fermion.The point in an orbit of a star in a double-star system in which thebody describing the orbit is nearest to the star.The point in the orbit of the Moon or an artificial Earth satellite, atwhich it is closest to Earth.The point in the orbit of a planet, comet, or artificial satellite in asolar orbit, at which it is nearest to the Sun.Positron Electron Tandem Ring Accelerator, an electron–positronstorageringatDESYinHamburg.Intensity maximum of secondary cosmic rays at an altitude of approximately15 km produced by interactions of primary cosmicrays in the atmosphere.Supersymmetric partner of the photon.Liberation of atomic electrons by photons.The gauge boson of electromagnetic interactions.Pauli principleperiastronperigeeperihelionPETRAPfotzer maximumphotinophotoelectric effectphotonπ; the lightest meson; pions constitute an isospin triplet the mem- pionbers of which have electric charges of +1, −1, or 0.Intensity distribution of blackbody radiation of a blackbody of temperatureT as a function of the wavelength following Planck’s radiationlaw.Scale, at which the quantum nature of gravitation becomes visible,L Pl = √ G¯h/c 3 ≈ 1.62 × 10 −35 m.Energy scale, at which all forces including gravity can be describedby a unified theory; m Pl = √¯hc/G ≈ 1.22 × 10 19 GeV/c 2 .A law giving the distribution of energy radiated by a blackbody.The frequency-dependent radiation density depends on the temperatureof the blackbody. See also Planck distribution.The tension of a typical string in string theories.The time taken for a photon to pass the distance equal to the Plancklength: t Pl = √ G¯h/c 5 ≈ 5.39 × 10 −44 s.A shell of gas ejected from and expanding about a certain kind ofextremely hot star.Planck distributionPlanck lengthPlanck massPlanck’s radiation lawPlanck tensionPlanck timeplanetary nebula