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

Having little or no hair on the scalp. → bald patch.

Bald from M.E. ball(e)d; Celtic bal "white patch, blaze;" Gk. phalios "having a white spot;" L. fulica "coot;" → patch.

Kal "bald," Mid.Pers. gar "bald;" Av. kaurva- "bald;" cf. Skt. kulva- "bald, thin-haired;" L. calvus "naked, bald."
Kacal may be related to kal.
Tâs, variant taz "bald;" Tabari tisâ, Saraxsi, Lâsgardi, Sangesari tusâ "empty;" related to tohi "empty;" Mid.Pers. tuhig; Av. taoš- "to become empty," pres. tusa-, caus. taošaya-, tusən "they lose their posture;" cf. Skt. tuccha-, tucchya- "empty;" L. tesqua, tesca "deserted place;" Russ. tošcij "hollow;" PIE base *teus- "to empty."

The location on the surface of the → Sun where → coronal  → magnetic field lines become tangent to the → photosphere. Bald patches play an important role in solar → magnetohydrodynamics.

→ bald, such called because of visual reference to a haircut (Titov et al. 1993, A&A 276, 564); → patch.

A set of nebular → emission line diagrams used to distinguish the ionization mechanism of → nebular gas. The most famous version consists of [N II]λ6584/Hα versus [OIII] λ5007/Hβ. The next two more commonly used BPT diagnostics are [S II] λλ6717,6731/Hα versus [O III] λ5007/Hβ and [O I] λ6300/Hα versus [O III]λ5007/Hβ. These diagrams use strong, optical lines of close proximity in the ratios to limit → reddening and → spectrophotometric effects. They are able to clearly distinguish different classes of → ionization, for example → LINERs from normal → H II regions and → active galactic nuclei.

Baldwin, J. A., Phillips, M. M., Terlevich, R., 1981 PASP 93, 5; → diagram.