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‖ penumbra|pɪˈnʌmbrə|
[mod.L. (Kepler, 1604), f. pene-, L. pæne almost + umbra shadow. Cf. F. pénombre (1671 in Hatz.-Darm.).]
1. The partially shaded region around the shadow of an opaque body, where only a part of the light from the luminous body is cut off; the partial shadow, as distinguished from the total shadow or umbra; esp. that surrounding the total shadow of the moon, or of the earth, in an eclipse, producing respectively a partial (or annular) eclipse of the sun, or a fainter obscuration bordering the full shadow on the disk of the moon.
[1604Kepler Ad Vitell. Paralipom. 239 Quod est inter KL,NM penumbra dicatur, LN vero umbra. 1709M. G. Hanschius (in Kepler's Wks. ed. Frisch III. 516) Umbræ penumbræque (quam primus ipse in astronomiam introduxit).] 1666Phil. Trans. I. 348 The Moon was not at all obscured by the true shadow, but entred only a little into the Penumbra. 1690Leybourn Curs. Math. 745 The Penumbra towards the perfect Shadow, does, little by little, grow more and more obscure. 1769Hirst in Phil. Trans. LIX. 231, I saw a kind of penumbra or dusky shade, which preceded the first external contact two or three seconds of time. 1812Woodhouse Astron. xxxv. 366 The time at which the Moon first enters the Earth's penumbra. 1869Tyndall Notes Lect. Light §12 If the source of light be a point, the shadow is sharply defined; if the source be a luminous surface, the perfect shadow is fringed by an imperfect shadow called a penumbra.
b. The lighter outer part or border of a sun-spot, surrounding the darker central nucleus or umbra.
1834M. Somerville Connex. Phys. Sc. xxxvii. (1849) 425 One of these spots..with its penumbra, occupied an area of 3780 millions of square miles. 1868Lockyer Guillemin's Heavens (ed. 3) 48 If the spot and its penumbra are formed by a conical opening, the sloping sides of which reveal to us the thickness of the envelopes.
c. Painting. (See quot.)
1826J. Elmes Dict. Fine Arts, Penumbra, in painting, drawing, &c., that point of a picture or drawing where the shade blends itself with the light... These gradations should be nearly imperceptible.
2. fig. A partial shade or shadow (in various metaphorical applications), esp. regarded as bordering upon a fuller or darker one.
1801M. Edgeworth Angelina iv, I will defend him, madam,..against every shadow, every penumbra of aristocratic insolence. 1836J. Abbott Way to do Good vi. 187 It is but a penumbra, a twilight of virtue and happiness. 1862Masson in Macm. Mag. Aug. 319 Those who can surround a definite designation with the due penumbra. |