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An observer in the penumbra experiences a partial eclipse. An alternative definition is that the penumbra is the region where some or all of the light source is obscured (i.e., the umbra is a subset of the penumbra). For example, NASA's Navigation and Ancillary Information Facility defines that a body in the umbra is also within the penumbra. [2]
Umbra, penumbra and antumbra. A point source of light casts only a simple shadow, called an "umbra". For a non-point or "extended" source of light, the shadow is divided into the umbra, penumbra, and antumbra. The wider the light source, the more blurred the shadow becomes. If two penumbras overlap, the shadows appear to attract and merge.
The moon’s penumbra causes partial solar eclipses. The super blood moon lunar eclipse occurred late in the night of Sunday, Jan. 20, 2019, and carried over into early morning Monday.
For the Sun, this light source is the photosphere. The antumbra (from Latin ante, 'before, in front of', plus umbra) extending beyond the tip of the umbra, within which the object is completely in front of the light source but too small to completely cover it. The penumbra (from the Latin paene, 'almost, nearly', plus umbra), within which the ...
The umbra may be surrounded completely or only partially by a brighter region known as the penumbra. [23] The penumbra is composed of radially elongated structures known as penumbral filaments and has a more inclined magnetic field than the umbra. [24] Within sunspot groups, multiple umbrae may be surrounded by a single, continuous penumbra.
The small area where the umbra touches Earth's surface is where a total eclipse can be seen. The larger light gray area is the penumbra, in which a partial eclipse can be seen. An observer in the antumbra, the area of shadow beyond the umbra, will see an annular eclipse. [20]
The penumbra causes a subtle dimming of the lunar surface, which is only visible to the naked eye when the majority of the Moon's diameter has immersed into Earth's penumbra. [8] A special type of penumbral eclipse is a total penumbral lunar eclipse , during which the entire Moon lies exclusively within Earth's penumbra.
Since Earth's diameter is 3.7 times the Moon's, the length of the planet's umbra is correspondingly 3.7 times the average distance from the Moon to the Earth: roughly 1,400,000 km (870,000 mi). The width of the Earth's shadow at the distance of the lunar orbit is approximately 9000 km (~ 2.6 lunar diameters), which allows people of the Earth to ...