Umbra

Umbra

"For other uses of the word "umbra", see Umbra (disambiguation)."

"For other uses of the word "penumbra", see Penumbra (disambiguation)."

The umbra, penumbra and antumbra are the names given to the three distinct parts of a shadow which are created when the source of light is not a point source. These names are usually used when referring to the shadows cast by celestial bodies.

In reality there is no such thing as a point source radiator, though in theory such a light source would cast an umbra, but not an antumbra or penumbra.

Umbra

The umbra (Latin: "shadow") is the darkest part of a shadow. From within the umbra, the source of light is completely concealed by the occulting body. In astronomy, an observer in the umbra is said to be experiencing a total eclipse.

Penumbra

The "penumbra" (Latin: "paenes" "almost, nearly" + "umbra" "shadow") the region in which only a portion of the occulting body is obscuring the light source. An observer in the penumbra experiences a partial eclipse.

Antumbra

The "antumbra" is the region from which the occulting body appears entirely contained within the disc of the light source. If an observer in the antumbra moves closer to the light source, the apparent size of the occulting body increases until it causes a full umbra. An observer in this region experiences an annular eclipse.


Wikimedia Foundation. 2010.

Игры ⚽ Нужна курсовая?
Synonyms:

Look at other dictionaries:

  • umbră — ÚMBRĂ, umbre, s.f. I. 1. Lipsă de lumină, întunecime provocată de un corp opac care opreşte razele de lumină; porţiune din spaţiu întunecoasă (şi răcoroasă) unde nu ajung direct razele de lumină. ♢ loc. adj. Fără umbră = corect, desăvârşit, pur.… …   Dicționar Român

  • Umbra — es un personaje ficticio del universo de Bionicle y representa a un guerrero gigante. Vive en Voya nui y protege la máscara Inika de la vida de los que la emplearían mal. Los grandes seres lo designaron como guardia de la máscara y de la Orden de …   Wikipedia Español

  • Umbra — (lat.: Kernschatten) bezeichnet: Umbra (Farbe), ein Pigment beziehungsweise dessen Farbe bestimmte Gebiete innerhalb von Sonnenflecken, die viel dunkler sind als die Sonnenoberfläche, siehe Penumbra (Astronomie) den Kernschatten bei einer… …   Deutsch Wikipedia

  • UMBRA — an ab imbre, quod omnes Umbrae humidae; an quod imbres obscurant lucem Solis; Perot. et Isidor. an a terra, cuius etiam color dicta Veteribus, humi chroa, χρόα enim Graecis color, post Humbra et Umbra, i. e. Terrae color? Becmann. aer est carens… …   Hofmann J. Lexicon universale

  • umbra — (del lat. «umbra»; ant.) f. *Sombra. * * * umbra. (Del lat. umbra). f. ant. sombra …   Enciclopedia Universal

  • umbra — ȕmbra ž <G mn ȗmbrā> DEFINICIJA 1. min. tamnosmeđa zemljana boja, vrsta okera 2. sjenka ETIMOLOGIJA lat. umbra: sjena …   Hrvatski jezični portal

  • Umbra — Um bra, n.; pl. {Umbr[ae]}. [L., a shadow.] 1. (Astron.) (a) The conical shadow projected from a planet or satellite, on the side opposite to the sun, within which a spectator could see no portion of the sun s disk; used in contradistinction from …   The Collaborative International Dictionary of English

  • Umbra — (römische Erde, römische Umbra, Schönrot, Türkischbraun, Umbrabraun, Umbraun), braune Erdfarben, neben als Farbensubstrat anzusehenden Kalk und Tonarten als färbende Hauptbestandteile vorwiegend Eisenoxydhydrat, wenn gelblich, Manganhydrat, wenn… …   Lexikon der gesamten Technik

  • umbra — (n.) 1590s, phantom, ghost, a figurative use from L. umbra shade, shadow (see UMBRAGE (Cf. umbrage)). Astronomical sense of shadow cast by the earth or moon during an eclipse is first recorded 1670s. Meaning an uninvited guest accompanying an… …   Etymology dictionary

  • umbra — (Del lat. umbra). f. ant. sombra …   Diccionario de la lengua española

  • Umbra [1] — Umbra (lat.), 1) der Schatten; 2) ein Tischgenoß bei römischen Gastmählern, welcher nicht von dem Gastgeber eingeladen, sondern von einem Gaste mitgebracht worden war …   Pierer's Universal-Lexikon

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”