The concept of aberration has multiple uses and meanings, as the dictionary reveals. The word, as it is officially accepted, may refer to a very serious error associated with the ability to understand; by acting depraved or perverse, which is far from what is considered lawful; the deviation from the normal type that, in certain situations, experiences a morphological or physiological character; or to the apparent deviation of the stars, among others.
The aberration in optical systems (such as mirrors, lenses or prisms) means a degradation of the images that occurs when light from a particular point of an object does not converge to a single point once transmitted through a system.
Other light- related aberrations that can be identified are spherical aberration (a defect characterized in that light rays incident parallel to the optical axis are deflected to a different focus) and chromatic aberration (alteration of the distance from the image with refractive index).
Aberration of light
The phenomenon that describes the different position of a star when observed with respect to the real one is called light aberration. James Bradley, a professor of astronomy at the University of Oxford, discovered this peculiarity in 1725, while seeking to establish the distance between a star and our planet. To do this, he made two observations, each at different times of the year, with the aim of achieving a more accurate triangulation of the star, thanks to the Earth’s orbital movement.
Bradley noted with amazement that the fixed stars presented a systematic translation that was linked to the direction of Earth’s motion in its orbit and that did not depend on the location of our planet in space, as previously believed. The highest value of variation between the observed and true position of a star is 20.47 arcseconds; this is known as the aberration constant. If we calculate its trigonometric tangent, we obtain a result very close to the ratio of the orbital speed of the Earth and that of light.
A chromosomal-type aberration constitutes an error that arises during gamete meiosis or when the first divisions of the egg take place, a phenomenon that triggers an abnormality that influences the number or composition of chromosomes. This phenomenon can cause multiple disorders, such as the development of the so-called Down syndrome.
The alteration can occur in the structure of the chromosome with respect to the linear ordering of genes, and the reasons are several, as well as their characteristics and consequences. We quote some below:
* Deletions: when a fragment of the chromosome is lost, either at one end or along one of its arms, generating an imbalance, appreciable in Prader-Willi syndrome;
* Duplications: causes a living being to contain too much genetic material, since a chromosomal region is duplicated, as occurs in fragile X syndrome;
* Inversions: it consists of the change of orientation of a segment of the chromosome, and does not usually cause considerable disorders. It can be pericentric, if the centromere is included in the inverted part, or paracentric, when it is not;
* Ring chromosome: This alteration is rare and consists of the fusion of both arms of a chromosome. Its development on the X chromosome is one of the causes of Turner syndrome;
* Translocations: describes the transfer of a portion of one chromosome to another, which does not imply loss or gain of genetic information.