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

1) The outermost portion of the Earth's → atmosphere. Extremely tenuous, it lies above the → ionosphere from a height of about 500 km, to the edge of → interplanetary space.
2) An extremely tenuous kind of atmosphere surrounding a → solar system body. Since the → mean free path is much greater than the atmospheric scale height. The → atoms or → molecules never collide with each other. → lunar exosphere.

→ exo- + → sphere.

The → photoelectric effect in solids where free electrons are emitted from the surface of a substance (e.g., → semiconductor) when radiation of appropriate frequency falls on it. Also called → photoemissive effect.

→ external; → photoelectric; → effect.

A → microorganism with the ability to thrive in extreme environmental conditions that would kill other species. These conditions include high temperatures, very low temperatures, high pressures, high levels of radiation, and high concentrations of salt in water.

→ extreme; → -phile.

Photoconductivity due to the addition of impurities or external causes.

→ extrinsic; → photoconductivity.

Šidhâzandegi, → photoconductivity; borungin, → extrinsic.

The 500 m diameter → radio telescope which is the largest → single-dish antenna in the world. It is an Arecibo type telescope nestled within a natural basin in China's remote and mountainous Dawodang, Kedu Town, in southeastern China's Guizhou Province. The → reflector consists of 4,450 triangular panels, each with a side length of 11 m. More than 2,000 → actuators are used, according to the feedback from the measuring system, to deform the whole reflector surface and directly correct for → spherical aberration. Several detectors are used to cover a frequency range of 70 MHz to 3 GHz.

→ five; → hundred; → meter; → aperture; → spherical; → radio; → telescope.

That part of the atmosphere where the effects of the ground on the → turbulence conditions are negligible.

→ free, → atmosphere.

The first phase of → supernova remnant (SNR) evolution in which the surrounding → interstellar medium (ISM) has no influence on the expansion of the → shock wave, and the pressure of the interstellar gas is negligible. The shock wave created by the → supernova explosion moves outward into the interstellar gas at highly → supersonic speed. Assuming that most of the → supernova energy  E_SN is transformed into → kinetic energy of the ejected gas, the ejection velocity v_e can be estimated from E_SN by using E_SN = (1/2) M_ev_e², which leads to v_e = (2E_SN / M_e)^(1/2), where M_e is the ejected mass. The schematic structure of the SNR at this phase can be described as follows: behind the strong → shock front which moves outward into the ISM, compressed interstellar gas accumulates forming a → shell of interstellar gas. This shell of swept-up material in front of shock does not represent a significant increase in the mass of the system. After some time the accumulated mass equals the ejected mass of stellar material, and it will start to affect the expansion of the SNR. By definition, this is the end of the free expansion phase, and the corresponding radius of the SNR, called → sweep-up radius, R_SW, is defined by M_e = (4π/3) R_SW³ρ₀, that is R_SW = (3M_e / 4πρ₀)^(1/3), where ρ₀ is the initial density of the ISM. This radius is reached at the sweep-up time t_SW = R_SW/v_e. The free expansion phase lasts some 100-200 years until the mass of the material swept up by the shock wave exceeds the mass of the ejected material. Then the following → snowplow phase starts.

→ free; → expansion; → phase.

A bright, third → magnitude (3.22) → giant star of → spectral type K1, also called → Errai, HR 8974, HIP 116727, and HD 222404. γCephei has a → surface temperature of 4920 K a mass of 1.40 Msun, a → luminosity 10.6 solar, and a radius 4.8 solar. Its distance is estimated to be 45 → light-years. γ Cephei will become the → Pole Star in about 2,000 years. γ Cephei has a low mass → companion (B), a main → main sequence star of spectral type M4 V with a mass of 0.4 Msun. It orbits the → primary star every 67.5 years. An → extrasolar planet. (γ Cephe b) has been discovered orbiting the main star.

Gamma, as in → Bayer designation; → Cepheus.

Of or pertaining to → geography.

→ geography; → -ic.

A → ccordinate system on the surface of the Earth that defines every location by a set of numbers and letters, indicating the → latitude and → longitude.

→ geographic; → coordinate; → system.

A synonym for → geodetic latitude or → astronomical latitude.

→ geographic; → latitude.

→ north pole.

→ geographic; → north; → pole.

→ south pole.

→ geographic; → south; → pole.

The science dealing with the areal differentiation of the Earth's surface, as shown in the character, arrangement, and interrelations over the world of such elements as climate, elevation, soil, vegetation, population, land use, industries, or states, and of the unit areas formed by the complex of these individual elements (Dictionary.com).

→ geo-; → -graphy.

The branch of physics that deals with the Earth and its environment, including meteorology, oceanography, seismology, and geomagnetism.

→ geo-; → physics.

Of or pertaining to the force produced by the rotation of the Earth.

From Gk. → geo- + Gk. strophe "a turning," from strephein "to turn," from PIE *strebh- "to wind, turn" + → -ic.

From zamin-, → geo-, + carxeši, → rotational.

Meteo.: The balance between the → Coriolis force and the → pressure gradient force. See also → geostrophic flow.

→ geostrophic; → balance.

Oceanography: A flow resulting from → geostrophic balance. In geostrophic flow water moves along the lines of constant pressure or → isobars. Geostrophic flow is characterized by small → Rossby and → Ekman numbers.

→ geostrophic; → flow.

Meteo.: A wind which is balanced by the → Coriolis effect and → pressure gradient force. An air parcel initially at rest will move from high pressure to low pressure because of the pressure gradient force. However, the air parcel in its movement is deflected by the Coriolis force, to the right in the northern hemisphere and to the left on the southern hemisphere. As the wind gains speed, the deflection increases until the Coriolis force equals the pressure gradient force. At this point, the wind will be blowing parallel to the → isobars.

→ geostrophic; → wind.

1) A visual representation of data that displays the relationship among variables, usually cast along X and Y axes.
2) In → graph theory, a graph G = (V, E) consists of a set of objects V called vertices and a set E which contains unordered pairs of distinct elements of V called edges.

Short for graphic (formula), from L. graphicus "of painting or drawing," from Gk. graphikos "able to draw or paint," from graph(ein) "to draw, write" + -ikos, → ic.

Negâré, from negâr "picture, figure" (verb negârdan, negâštan "to paint"), from prefix ne-, O.Pers./Av. ni- "down; into," → ni-, + gâr, from kar-, kardan "to do, to make" (Mid.Pers. kardan; O.Pers./Av. kar- "to do, make, build;" Av. kərənaoiti "he makes;" 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").