Definition of
Nebula
The concept of nebula used in the field of astronomy to allude to a cosmic matter formed by a combination of gases and dust, whose limits are not precise. The nebula, a term that derives from the Latin word nebulōsuscan take different forms.
He helium and the hydrogen They are the most common components of nebulae. This matter can be generated with remnants of stars that have already died outalthough it can also constitute the ingredient that gives rise to new stars from a process of aggregation and of condensation.
The emission nebulae are the most common. In these nebulae, the gases they are transformed by ultraviolet radiation from the nearest stars, and that is why they shine brightly. In the field of astrophysics, these nebulae are called H II Regions and it is an indispensable element in the analysis of the physical properties and chemical composition of nebulae.
One of the reasons why emission nebulae are so important to astrophysics is the large number of emission lines of their chemical elements. The brightest and most relevant of them is H-alphawhich is located in the zone red of the spectrum and explains why this color predominates in the images that are captured of these nebulae.
The absorption nebulae either dark nebulaeon the other hand, are far from the stars and they are not under its influence: therefore they do not emit light. They are accumulations of interstellar dust and gas that are not related to any star, and it is for this reason that they do not receive energy and their presence can only be noticed by contrasting them with a very starry background that is at a great distance.
In the peripheral zone of an absorption nebula, the stars behind it are reddish in color and less intense precisely because the material in the former tends to absorb their energy. light. Because some absorption nebulae are between our galaxy and the Sun, on moonless nights it is possible to notice certain “spots” in the sky.
Some of the easier to distinguish absorption nebulae in our galaxy are sack of coal and Horse’s head (The latter can be seen with a medium telescope, which is why many people know about it.) It is worth mentioning that in other galaxies, beyond our own, there are also nebulae of this type. If they are studied by infrared radiation, forming stars are sometimes detected within them.
The reflection nebulaeFinally, they manage to reflect the light of the nearest stars, but since these are not very hot, they do not emit the ultraviolet radiation that is required for the excitation of the gas in the nebula. In general, they are made up of residues of the gas that created the star and its spectrum resembles that of those whose light they reflect. The best known of this type is the nebula around Meropea star in the open cluster of the seven sistersbelonging to the constellation Taurus.
Beyond the astronomical, the idea of a nebula is used to refer to that which develops in a unclear and to state of bewilderment either hesitation. These meanings are linked to the first uses of nebula which, until the creation of the telescope, referred to celestial bodies that appeared diffuse before the eyes of the observer.
By example: “My brother-in-law told me about a business initiative yesterday, but it seemed a bit nebulous to me”, “Could you tell me what’s going on here? I’m in a haze”.