The Latin word cumŭlus came to Castilian as cumulus. The concept can be used to name the accumulation or disorderly piling up of various elements.
For example: “When the meeting ended, I experienced a host of sensations”, “My life is a host of problems, I need vacations”, “The host of government errors caused this social crisis”.
In this framework, if someone refers to the “cumulative difficulties” that they had to go through to reach a goal, they will be referring to all the inconveniences that they had to overcome to achieve their goal.
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In the field of astronomy, on the other hand, a cluster of small stars that is thick in sight is called a cluster. Star clusters are generated by the attraction produced by the mutual gravity of stars.
According to the traditional classification, it is possible to distinguish open star clusters from globular ones. Open clusters are made up of young stars (which can be between a hundred and a billion years old), while globular clusters are made up of old stars, which can be over a billion years old.
Open clusters, on the other hand, have fewer stars than globular clusters. They also disintegrate over time due to their interaction with molecular clouds as they move through the galaxy, whereas globular clouds have higher degrees of stability and density, making them less prone to disintegration, although this does not prevent them from falling apart. Sooner or later they will be destroyed.
Beyond the differences in the number of stars (which inevitably affects the mass of both types of clusters) and the age of each one, it is also possible to distinguish them by the richness in metals they present (the open ones exceed the globular ones in this aspect) and by its orbit (the globular ones belong to the halo population, and the open ones to the disk population).
Despite all that has been said, the dimensions of their cores are not very different: both in open and globular clusters, it can be measured in a few parsecs (the unit called parsec or parsec is used in the field of astronomy and its definition is the distance at which an astronomical unit joins with an angle of arc one second).
In the 1980s and 1990s, some researchers discovered that this classification was not sufficient to include all types of star clusters that exist. In the Magellanic Clouds, to cite an example, there are clusters of dimensions comparable to those of the globular ones, although of an age that does not allow them to be placed in this group. Star clusters with similar characteristics have also been discovered outside our galaxy, with masses much higher than those of globular ones, and they are called superclusters.
In the Milky Way there are also superclusters, and some of them are behind huge clouds of dust. It is important to distinguish star clusters from stellar associations, groupings that are not held together by gravity and that exhibit slow dispersal.
In the field of meteorology, cumulus clouds are groups of clouds characteristic of the summer season, which resemble snowy mountains. Also called cumulus clouds, these clouds have a prominent vertical development and their edges are bright and well defined.
For geology, a cluster is the gathering of crystals in magma. The notion is also used to name the rock that results from this accumulation process.
Cytology, finally, appeals to the idea of cluster differentiation to refer to the antigens found on the surface of leukocytes, used to identify the type of cell and its activity.