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

The diaphragm that limits the diameter of the axial light bundle allowed to pass through a lens.

→ aperture; → stop.

Light that is reflected from a curved surface mirror.

→ catoprtics; → light.

An optical system in which the light is reflected only.

→ catoprtics; → system.

The area of → optics which treats of the laws and properties of light reflected from reflective surfaces.

From Gk. katoptrikos, from katoptron "mirror" (from kat-, → cata-, + op- "to see," → optics, + -tron suffix of instruments) + -ikos, → -ics.

Bâztâbik, from bâztâb, → reflection, + -ik, → -ics.

An → isotope not itself → fissile but that is converted into a fissile isotope, either directly or after a short → decay process following absorption of a → neutron. Example: U-238 can capture a neutron to give U-239. U-239 then decays to Np-239 which in turn decays to fissile Pu-239. The most important fertile isotope is U-238. This is by far the most abundant isotope of natural uranium, making up 99.28%. The important transformation chain is: ₉₂U²³⁸ + ₀n¹→ ₉₃Np²³⁹ + β^- (23.5 minutes) → ₉₄Pu²³⁹ + β^- (2.36 days).

→ fertile; → isotope .

A diaphragm located at an image plane of an optical system that determines the size and shape of the image. → aperture stop.

→ field; → stop.

An isotope that is capable of undergoing nuclear fission after capturing either fast neutron or thermal neutron. Typical fissionable isotopes: ²³⁸U, ²⁴⁰Pu, but also ²³⁵U, ²³³U, ²³⁹Pu, ²⁴¹Pu

→ fissile; → isotope .

One of two or more atoms having the same number of protons in its nucleus, but a different number of neutrons and, therefore, a different mass.

Isotope, from → iso- + -tope, from Gk. topos "place."

Izotop, loan from Fr., as above. hamjâ, from ham- "together" → com- + jâ "place" (from Mid.Pers. giyag "place;" O.Pers. ā-vahana- "place, village;" Av. vah- "to dwell, stay," vanhaiti "he dwells, stays;" Skt. vásati "he dwells;" Gk. aesa (nukta) "to pass (the night);" Ossetic wat "room; bed; place;" Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night").

A slight difference between the → abundances of → isotopes of the same → chemical element owing to → physical or → chemical  → processes. It results in the → enrichment or → depletion of an isotope. Same as → isotopic fractionation.

→ isotope; → fractionation

A displacement in the spectral lines due to the different isotopes of an element.

→ isotope; → shift.

Of or relating to an → isotope.

→ isotope; → -ic.

Same as → isotope fractionation.

→ isotopic; → fractionation

The difference between the number of neutrons in an isotope and the number of protons. Neutron excess.

→ isotopic; → number.

The relative abundances of two isotopes of a given chemical element, such as D/H (deuterium/hydrogen), (carbon) ¹²C/¹³C, and (uranium) ²³⁵U/²³⁸U.

→ isotopic; → ratio.

Same as → isospin.

→ isotopic; → spin.

Any of molecular entities which differ in their isotopic composition but retain the same → chemical elements, e.g. H₂O and HDO.

Abbreviation of → isotopic → analogue.

Any of → isomers having the same number of each isotopic atom but differing in their positions. For example, CH₃CHDCH₃ and CH₃CH₂CH₂D are a pair of isotopomers.

Short for isotopic isomers.

The boundary layer between a planet's → magnetosphere and the → magnetic field of the → solar wind. It borders the → magnetosheath and is defined by the surface on which the pressure of the solar wind is balanced by that of the planet's magnetic field. The front point of the Earth's magnetopause, on the sun-ward side of the Earth, is about 10 terrestrial radii, on average. This point can be closer or farther, because the magnetopause contracts or expands depending on the intensity of the solar wind.

From → magneto- + pause "break, cessation, stop," from M.Fr. pause, from L. pausa "a halt, stop, cessation," from Gk. pausis "stopping, ceasing," from pauein "to stop, to cause to cease."

From meqnât-→ magnet + marz "frontier, border, boundary," from Mid.Pers. marz "boundary;" Av. marəza- "border, district," marəz- "to rub, wipe;" Mod.Pers. parmâs "contact, touching" (→ contact), mâl-, mâlidan "to rub;" PIE base *merg- "boundary, border;" cf. L. margo "edge" (Fr. marge "margin"); Ger. Mark; E. mark, margin.

A stage in the formation of a → planet, which comes about from the aggregation of → planetesimals. The protoplanet eventually becomes a planet by → accretion of material from a → protoplanetary disk.

→ proto- + → planet.

Of or relating to a → protoplanet or protoplanets.

→ protoplanet; → -ary.