penumbra

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penumbra

(pĭnŭm`brə): see eclipseeclipse
[Gr.,=failing], in astronomy, partial or total obscuring of one celestial body by the shadow of another. Best known are the lunar eclipses, which occur when the earth blocks the sun's light from the moon, and solar eclipses, occurring when the moon blocks the sun's light
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; sunspotssunspots,
dark, usually irregularly shaped spots on the sun's surface that are actually solar magnetic storms. The spots are darker because the temperature of the spots is lower than that of the surrounding photosphere (the visible surface of the sun).
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.

penumbra

(pi-num -bră)
1. See umbra.
2. See sunspots.

Penumbra

 

the space between regions of total shadow and total light formed behind an opaque body illuminated by a light source whose dimensions are comparable both with the dimensions

Figure 1

of the body and with the distance from the light source to the body (see Figure 1). Only part of the light source is visible in the penumbra; the light source is not visible in the umbra and is completely visible in the region of total light. The point of observation of a partial solar eclipse is within the penumbra formed by the moon as illuminated by the sun.

penumbra

[pə′nəm·brə]
(astronomy)
The outer, relatively light part of a sunspot.
(optics)
That portion of a shadow illuminated by only part of a radiating source.

penumbra

1. a fringe region of half shadow resulting from the partial obstruction of light by an opaque object
2. Astronomy the lighter and outer region of a sunspot
3. Painting the point or area in which light and shade blend
References in periodicals archive ?
CONCLUSION: PCT is a better non-invasive modality for diagnosis of infarct, penumbra and normal brain regions based on quantitative perfusion parameters especially rCBV, CBV ratio and CBF ratio.
Penumbra pattern assessment in acute stroke patients: comparison of quantitative and non-quantitative methods in whole brain CT perfusion.
Quantitative Evaluation of the Penumbra and Ischemic Core in Acute Cerebral Infarction Using Whole-Brain CT Perfusion.
sup][2] The role of perfusion neuroimaging in the management of AIS is to confirm the presence of reduced regional blood flow and contribute to the identification of the ischemic penumbra that might be salvaged by thrombolytic and/or endovascular recanalization therapy.
sup][5],[6],[7],[8] In this study, ischemic penumbra was defined by decreased ASL CBF area, except in the restricted diffusion area.
When the sunspot is in the last phase of dissolution, the penumbra is less regularly radiated, and it seems formed of the thinnest and most tenuous part of the photosphere itself.
Caracteristicas de la penumbra de la mancha mayor del grupo, b-Poblacion del grupo segun McIntosh con la modificacion aplicada en Cuba, c-Tipo de grupo segun la clasificacion de Zurich, d-Numero de poros, e-Area de los grupos de manchas en millonesimas de semiesfera y f-Clasificacion magnetica.
Tamano y simetria de la penumbra de la mancha mayor del grupo, segun McIntosh