The penumbra is a weak shadow that appears between darkness and light.
Penumbra is a notion that comes from a compound Latin word: paene ( "almost" ) and umbra ( "shadow" ). It is, therefore, the weak shadow that exists between light and darkness and that prevents us from perceiving where one begins and the other ends.
For example: "The murderer waited in the dark until the victim burst into the room" , "Please turn on the light: I can't read in the dark" , "My husband took me to dinner at a very romantic restaurant, where We ate in the dark and listened to classical music .
Features of the penumbra
In darkness, the light source is partially blocked , unlike in darkness. That is why the darkness allows us to see certain shapes or colors, although it does not allow them to be seen clearly.
If there is a man standing on a dark street, it is likely that another person will notice his presence, but will not be able to recognize him or know how he is dressed, since there will not be enough lighting to capture details.
The term in astronomy
For astronomy , the penumbra is the partial shadow that appears between the spaces that are completely illuminated and those that are entirely in darkness during an eclipse. In this sense, a distinction can be made between penumbra , antumbra and umbra .
For a lunar eclipse to occur, it is necessary for the moon to be partially or totally located in the cone of shadow that the Earth projects as a result of the light it receives from the Sun, and which is determined by the outer tangent conical areas of our planet and the star. On the other hand, there is the twilight zone, which presents a decreasing level of illumination as it approaches said shadow cone, and which is determined by the inner tangent conical surfaces of the Earth and the Sun.
Eclipses produce a penumbra.
The penumbra in an eclipse
During an eclipse, the penumbra is characterized by the fact that anyone who, located on its surface, tries to observe the Sun, can only see part of it. The same thing happens during lunar eclipses, when there are some areas of shadow and some areas of penumbra, or only the latter type (in this case, it is practically impossible to perceive the difference in luminosity of the surface of the moon with the naked eye). , which is why it is usually studied by capturing digital images).
An eclipse is total if the lunar disk is completely covered by the umbra (the shadow of the cone projected by the Earth), partial if only part of it is shadowed, and penumbral if the satellite only manages to partially or completely enter the penumbra of the Earth. . As mentioned above, since the shadow of the penumbra is not very intense, it is very difficult to perceive a penumbral eclipse with the naked eye. It is important to understand that the total eclipse causes the Moon to pass through the penumbra at the beginning and end and to pass through the umbra completely during its process.
The notion in oncology
Within the field of radiation oncology, the term penumbra is used to name the area that constitutes the periphery of the main focus of x-ray treatment.
This concept is defined as the lateral distance between 80% and 20% of the isodose and its order of magnitude is the same as the result of the measurements taken in the ionization chamber.
Penumbra as a name or title
Penumbra , on the other hand, is the name of a French gothic metal band that was founded in 1996 and that, to date, has released four albums.
A PC video game saga that started in 2007 is also known as Penumbra . The first game was called Penumbra: Overture and was followed by Penumbra: Black Plague and Penumbra: Requiem .