An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

One of several peaks appearing in the → CMB angular power spectrum of the → cosmic microwave background radiation which are ripples left by acoustic oscillations of the plasma-radiation fluid in the early Universe (→ baryon acoustic oscillations). When the Universe was small and very hot, the free electron density was so high that photons could not propagate freely without being scattered by electrons. Ionized matter, electrons and radiation formed a single fluid, with the inertia provided by the baryons and the radiation pressure given by the photons.

→ acoustic; → peak.

The uplift of the central parts of the → crater floor due to the impacting force of a large → meteorite. The shock wave entering the Earth will first move in as a compressional wave (P-wave), but after passage of the compressional wave an expansion wave (rarefaction wave) will move back toward the surface. This will cause the floor of the crater to be uplifted and may also cause the rock around the rim of the crater to bent upward.

→ central; → peak.

A crucial period in the history of the → Universe, when the bulk of stars in massive galaxies were likely formed. Observations of young stars in distant galaxies at different times in the past have indicated that the → star formation rate peaked at the → redshift of z ~ 2, some 10 billion years ago, before declining by a factor of around ten to its present value (P. Madau & Dickinson, 2014, arXiv:1403.0007).

→ cosmic; → star; → formation; → peak.

In nuclear fusion, the product of the Maxwell-Boltzmann distribution with the tunnelling probability of the nuclei through their Coulomb barrier. This is the energy region where the reaction is more likely to take place: at higher energies, the number of particles becomes insignificant while at lower energies the tunnelling through the Coulomb barrier makes the reaction improbable.

→ Gamow barrier; → peak.

A bump appearing in the plot of stellar → opacity versus temperature. The ionization of the heaviest → chemical elements, especially → iron, which is the most abundant heavy metal, produces a large number of weak spectral → absorption lines. These lines dominate the stellar opacity in the temperature range 10⁵-10⁶ K and furnish two local opacity peaks: a large peak around 2 × 10⁵ K and a smaller one around 1.5 × 10⁶ K (Rogers & Iglesias, 1992, ApJS 79, 507; Iglesias et al. 1992, ApJ, 397, 717).

→ iron; → opacity; → peak.

A maximum on the element-abundance curve in the vicinity of the iron → atomic number 26. The relative higher abundance of the → iron peak elements results from their being the end products of → nucleosynthesis in the interiors of → massive stars.

→ iron; → peak.

A member of a group of elements with → atomic masses A about 40 to 60 that are synthesized by the → silicon burning process and appear in the → iron peak. They are mainly: → titanium (Ti), → chromium (Cr), → manganese (Mn), → iron (Fe), → cobalt (Co), and → nickel (Ni).

→ iron; → peak; → element.

A device in which electric signals are converted into audible sound.

→ loud; → speak; → -er.

The pointed top of a mountain or ridge. The pointed top of anything. → Gamow peak; → peak wavelength.

Perhaps from M.L.G. pék "pick, pike."

Setiq "summit, top," from *us-tig, from us-, → ex-, + tig "pointed," related to tiq "blade," tiz "sharp," tež, tej, tij; Mid.Pers. tigr, têz, têž "sharp," O.Pers. tigra- "pointed," tigra.xauda- "pointed helmet (epithet of Scythians)," Av. tiγra- "pointed," tiγray- "arrow," tiži.arštay- "with the pointed spear," cf. Skt. tikta- "sharp, pungent, bitter," tejas- "sharpness, edge, point or top of a flame;" PIE base *st(e)ig- "to stick; pointed." Cognates in other IE languages: Gk. stizein "to prick, puncture," stigma "mark made by a pointed instrument," L. in-stigare "to goad," O.H.G. stehhan, Ger. stechen "to stab, prick," Du. stecken, O.E. sticca "rod, twig, spoon," E. stick.

The → bolometric luminosity of a → supernova corresponding to the highest brightness in its → light curve. The peak luminosity occurs after the → supernova explosion; it is directly linked to the amount of radioactive ⁵⁶Ni produced in the explosion and can be used to test various explosion models. Following → Arnett's rule, one can derive the ⁵⁶Ni mass from the peak luminosity of a → Type Ia supernova.

→ peak; → luminosity.

The wavelength at which the radiant intensity of a source is maximum.

→ peak; → wavelength.

To utter words with the ordinary voice (not singing) to communicate; to talk.

From M.E. speken "to speak," from O.E. specan, alteration of earlier sprecan "to speak;" cf. Low Germ. spreken "to speak," Du. spreken, Ger. sprechen "to speak;" ultimately from PIE *spreg- "to make a sound, utter, speak."

From M.P. saxwanitan "to speak, to talk," → speech.