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

Not soft; severe.
Physics: Having relatively high energy (of a beam of particles or photons); → hard X-rays; opposed to → soft.

Hard, from O.E. heard "solid, firm; severe, rigorous," from P.Gmc. *kharthus (cf. Du. hard, O.H.G. harto "extremely, very," Goth. hardus "hard"), from PIE *kratus "power, strength" (cf. Gk. kratos "strength," kratys "strong").

Saxt "hard, strong, firm, secure, solid, vehement, intense," from Mid.Pers. saxt "hard, strong, severe;" Av. sak- "to understand or know a thing, to mark;" cf. Skt. śakta- "able, strong," śaknoti "he is strong," śiksati "he learns."

In → stellar dynamics studies of → three-body encounters, a → binary system whose → binding energy far exceeds the → kinetic energy of the relative motion of an incoming third body. In such an encounter, a hard binary is likely to get harder and transfer energy to the incoming star, whereas a → soft binary is likely to be disrupted.

→ hard; → binary.

The front, bony part of the roof of the mouth. → soft palate.

→ hard; → palate.

The short wavelength, high energy end of the → electromagnetic spectrum. Hard X-rays are typically those with energies greater than around 10 keV. The dividing line between hard and → soft X-rays is not well defined and can depend on the context.

→ hard; → X-rays.

Any physical equipment. The physical equipment comprising a computer system; opposed to → software.

→ hard + ware, from M.E., from O.E. waru, from P.Gmc. *waro (cf. Swed. vara, Dan. vare, M.Du. were, Du. waar, Ger. Ware "goods").

Saxt-afzâr, from saxt, → hard + afzâr "instrument, means, tool," from Mid.Pers. afzâr, abzâr, awzâr "instrument, means," Proto-Iranian *abi-cāra- or *upa-cāra-, from cāra-, cf. Av. cārā- "instrument, device, means" (Mid.Pers. câr, cârag "means, remedy;" loaned into Arm. aucar, aucan "instrument, remedy;" Mod.Pers. câré "remedy, cure, help"), from kar- "to do, make, build;" kərənaoiti "he makes" (Pers. kardan, kard- "to do, to make"); cf. Skt. kr- "to do, to make," krnoti "he makes, he does," karoti "he makes, he does," karma "act, deed;" PIE base k^wer- "to do, to make").

(adj.) Of, pertaining to, or noting a series of oscillations in which each oscillation has a frequency that is an integral multiple of the same basic frequency.
(n.) A wave motion, superimposed on a fundamental wave, having a frequency which is an integral multiple of the fundamental frequency. → overtone.

From L. harmonicus, from Gk. harmonikos "harmonic, musical," from harmonia "agreement, concord of sounds," related to harmos "joint," arariskein "to join together;" PIE base *ar- "to fit together."

Hamâhang, "harmonious, concordant," from ham- "together, with; same, equally, even" (Mid.Pers. ham-, like L. com- and Gk. syn- with neither of which it is cognate. O.Pers./Av. ham-; Skt. sam-; also O.Pers./Av. hama- "one and the same," Skt. sama-; Gk. homos-; originally identical with PIE numeral *sam- "one," from *som-) + âhang "melody, pitch, tune; harmony, concord," from Proto-Iranian *āhang-, from prefix ā- + *hang-, from PIE base *seng^wh- "to sing, make an incantation;" cf. O.H.G. singan; Ger. singen; Goth. siggwan; Swed. sjunga; O.E. singan "to chant, sing, tell in song;" maybe cognate with Gk. omphe "voice; oracle."

A number whose reciprocal is the → arithmetic mean of the reciprocals of a set of numbers. Denoted by H, it may be written in the discrete case for n quantities x₁, ..., x_n, as: 1/H = (1/n) Σ(1/x_i), summing from i = 1 to n. For example, the harmonic mean between 3 and 4 is 24/7 (reciprocal of 3: 1/3, reciprocal of 4: 1/4, arithmetic mean between them 7/24). The harmonic mean applies more accurately to certain situations involving rates. For example, if a car travels a certain distance at a speed speed 60 km/h and then the same distance again at a speed 40 km/h, then its average speed is the harmonic mean of 48 km/h, and its total travel time is the same as if it had traveled the whole distance at that average speed. However, if the car travels for a certain amount of time at a speed v and then the same amount of time at a speed u, then its average speed is the arithmetic mean of v and u, which in the above example is 50 km/h.

→ harmonic; → mean.

A motion that repeats itself in equal intervals of time (also called periodic motion).

→ harmonic; → motion.

Any oscillating particle in harmonic motion.

→ harmonic; → oscillator.

Math.: Any ordered set of numbers, the reciprocals of which have a constant difference between them. For example 1, ½, 1/3, ¼, ..., 1/n. Also called → harmonic sequence.

→ harmonic; progression.

→ harmonic progression.

→ harmonic; → sequence.

Overtones whose frequencies are integral multiples of the → fundamental frequency. The fundamental frequency is the first harmonic.

→ harmonic; → series.

A type of galaxies characterized by strong emission in the blue and violet regions of the spectrum. They are often elliptical or lenticular.

Named after the Mexican astronomer Guillermo Haro (1913-1988), who first compiled a sample of these objects; → galaxy.

A → polarimeter using the → spectrographic capabilities of the → High Accuracy Radial velocity Planet Searcher (HARPS) to measure the → Zeeman effect indicating the presence of a → magnetic field at the surface some stars. This combined instrument is installed at the ESO 3.6-m telescope at → La Silla Observatory (Chile) and covers the 3800-6900 Å wavelength region with an average → spectral resolution of 110,000 (Piskunov, et al., 2011, ESO Messenger 143, 7). HARPSpol is mainly used in research on → magnetic fields in stars. See also → magnetic star, → magnetic massive star, → magneto-asteroseismology

→ HARPS + -pol, from → polarimeter.

A number that is divisible by the sum of its digits. For example, 18 is a Harshad number because 1 + 8 = 9 and 18 is divisible by 9 (18/9 = 2). The simplest Harshad numbers are the two-digit Harshad numbers: 10, 12, 18, 20, 21, 24, 27, 30, 36, 40, 42, 45, 48, 50, 54, 60, 63, 70, 72, 80, 81, 84, 90. They are sometimes called Niven numbers.

The name Harshad was given by Indian mathematician Dattaraya Kaprekar (1905-1986) who first studied these numbers. Harshad means "joy giver" in Sanskrit, from harṣa- "joy" and da "to give," → datum.

A proposal regarding the initial state of the → Universe prior to the → Planck era. This → no boundary hypothesis assumes an imaginary time in that epoch. In other words, there was no real time before the → Big Bang, and the Universe did not have a beginning. Moreover, this model treats the Universe like a quantum particle, in an attempt to encompass → quantum mechanics and → general relativity; and attributes a → wave function to the Universe. The wave function has a large value for our own Universe, but small, non-zero values for an infinite number of other possible, parallel Universes.

Hartle, J., Hawking, S., 1983, "Wave function of the Universe," Physical Review D 28; → initial; → state.

A band in the → absorption spectrum of → ozone (O₃) extending in the → ultraviolet from 200 nm to 300 nm. It is stronger than the → Huggins band. See also: → Hartley band.

W. N. Hartley, J. Chem. Soc. 39, 111 (1881).

A way of testing the quality of optical systems. In this method, incident rays from a point source are isolated by small holes in an opaque screen located close to the lens or mirror under test. Photographic plates are inserted into the beam within and beyond the focal region. The black dots on the exposed plates, which reveal differences of optical focus in the various zones of the lens or mirror, are analyzed to yield the objective's figure. → Shack-Hartmann wavefront sensor.

Named after the German astronomer Johannes Hartmann (1865-1936), who developed the method. → test.

A unit of energy used in atomic and molecular physics; symbol Ha or E_h. It is defined as: 1 Ha = m_ee⁴/(4ε₀²ħ), where m_e is the mass of electron, e its charge, ε₀ the → permittivity of vacuum, and ħ → reduced Planck's constant. Its value is 2 → rydbergs, or 4.3597 x 10^-18 → joule, or 27.213 → electron-volts.

Named for the British physicist and mathematician Douglas R. Hartree (1897-1958).

A classification of stellar spectra published in the Henry Draper catalogue, which was prepared in the early twentieth century by E. C. Pickering and Miss Annie Canon. It is based on the characteristic lines and bands of the chemical elements. The most important classes in order of decreasing temperatures are as follows: O, B, A, F, G, K, M.

Harvard, named for John Harvard (1607-1638), the English colonist, principal benefactor of Harvard College, now Harvard University. → classification