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

In → graph theory, an → ordered tree with all → nodes having at most two → children.

→ binary; → tree.

A diagram representing a systematic way of determining all the prime factors of a number.

→ factor; → tree.

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 method used in → numerical simulations for studying the growth and development of galaxies and → dark matter halos. Within the currently accepted ΛCDM cosmology, dark matter halos merge from small → clumps to ever larger structures. This merging history can be traced in simulations and stored in the form of merger trees. Merger trees are necessary because a galaxy may have more than one → progenitor at an early time.

→ merger; → tree.

In → graph theory, a → tree in which the → children of each → vertex are ordered.

→ ordered; → tree.

In → graph theory, a → tree in which one → vertex is distinguished from the other vertices and is called the root.

→ root; → tree.

1) A tall, woody perennial plant usually with a single trunk.
2) Math.: → factor tree.
3) A → data structure that is used to represent hierarchical data.
4) In → graph theory, a → connected graph with no → cycles.
5) A mathematical structure that can be viewed as either a graph or as a data structure. Many powerful algorithms in computer science and software engineering are tree based algorithms.

M.E., from O.E. treo, treow "tree, wood," from P.Gmc. *trewan (cf. O.S. trio, O.N. tre, Goth. triu), from PIE *deru- "wood" (cf. Mod.Pers. dâr "tree;" O.Pers. dāruv- "wood;" Av. dāuru- "piece of wood, tree trunk;" Skt. dāru- "tree, wood;" Gk. drus "tree;" Serb. drvo "tree;" L. larix "larch tree;" Rus. drevo "tree, wood;" Pol. drwa "wood;" Lith. derva "pine wood;" O.Ir. daur, Welsh derwen "oak").

Deraxt "tree;" Mid.Pers. draxt "tree," two possible etymologies. A suffixed variant of dâr "tree," cognate with E. tree, as above. Alternatively, from Av. *draxta- "firmly stood, fixed" (as in handraxta-), from drang-, dranj- "to fix, fasten, strengthen, hold," dražaite "holds," infinitive drājnhe; cf. Khotanese drys- "to hold;" Sogdian drγ- "to hold;" Parthian Mid.Pers. drxs "to endure."

A type of → data structure in which each element is attached to one or more elements in a hierarchical manner. Trees are often called inverted trees because they are normally drawn with the root at the top.

→ tree; → structure.

A graphical representation that displays a hierarchical view of data.

→ tree; → view.