Penumbra Sentence Examples
The notions of the penumbra and umbra are important in considering eclipses (q.v.).
In the neighbourhood surrounding the penumbra the granules appear to be packed more closely, forming brilliant patches called faculae.
A partial lunar eclipse occurs when the Moon passes into the penumbra, or partial shadow.
It is surrounded by the penumbra that receives some light from the light source.
Group differences in average volume of ischaemic penumbra salvaged will be analyzed by t-test, adjusting for baseline differences in prognostic variables.Advertisement
All but the smallest spots show a dark central portion called the umbra with a lighter outer area called the penumbra.
Well, consider the following penumbra of events that surround the current rumpus.
The amount of want of illumination in each portion of the penumbra is roughly indicated by the shading.
The first, taken alone, might seem to bear out Wilson's theory, but the others show that the penumbra is really very unsymmetrical and much broader on the side towards the limb, apart from anything which perspective may have to say.
He pointed out that they were limited to a certain defined zone on the sun's surface; he noted the faculae with which they are associated, the penumbra by which they are bordered, their slight proper motions and their rapid changes of form.Advertisement
The breadth of the penumbra when the source and screen are nearly equidistant from the opaque body is equal to the diameter of the luminous source.
Some lines of certain elements are always seen fainter or thinner than on the photosphere, or even wholly obliterated; others sometimes show the same features, but not always; other lines of the same elements, perhaps originating at a level above the spot, are not affected; there are also bright streaks where even the general absorption of the spot is absent, and sometimes such a bright line will correspond to a dark line on the photosphere; most generally the lines are intensified, generally in breadth, sometimes in darkness, sometimes in both together, sometimes in one at the expense of the other; certain lines not seen in the photosphere show only across the umbra, others cross umbra and penumbra, others reach a short distance over the photosphere.
If we suppose the number of sources to increase indefinitely, so as finally to give the appearance of a luminous surface as the source of light, it is obvious that the degrees of darkness at different portions of the penumbra will also increase indefinitely; i.e.
Each spot shows with more or less completeness a ring-shaped penumbra enclosing a darker umbra; the umbra, which looks black beside' the photosphere, is actually about as brilliant as limelight.
To draw a trustworthy conclusion it is necessary that the spot should be quiescent, show a well-developed and fairly symmetrical penumbra, and be observed near the limb and also near the centre, and these conditions are satisfied in so few cases as to withdraw all statistical force from the conclusion.Advertisement
But if we place a body at a distance of a foot or two only from the arc, the shadow cast will have as much of penumbra as if the sun had been the source.
When the slit of the spectroscope is set across a spot, it shows, as might be expected, a general reduction of brightness as we pass from the photosphere to the penumbra; and a still greater one as we pass to the umbra.
The penumbra remains the penumbra, but it is now darkest where before it was brightest, and vice versa.