Variable star, definition and study. A-Z index of Cognitio.

A variable star is a star whose apparent brightness changes over time. They may have variations ranging from a few millisecond magnitudes to twenty magnitudes in periods ranging from fractions of the second to the years. Many stars, perhaps most of them, change brightness over time. The Sun is no exception: its brightness is 0.1% in its undeclared cycle.Sun, definition and study. A-Z index of Cognitio.

The first variable star to be recognized as such by Mira: in 1638 Johannes Holwarda noted that it changed its brightness over a period of 11 months.Mira, definition and study. A-Z index of Cognitio.

Variable stars are generally analyzed using photometric, spectrophotometric and spectroscopic techniques. The measurements of their photometric changes can be used to plot the graph of the light curve, which shows the trend of the amount of radiation emitted by the star over time. The first variable stars discovered in a constellation are assigned letters from R to Z, for example, R Coronae Borealis.Coronae Borealis, definition and study. A-Z index of Cognitio.

Variable stars can be divided into several categories:

The pulsating variables, in which the radius expands and contracts periodically.Pulsating variables, definition and study. A-Z index of Cognitio.

Eruptive variables, which experience bulges and mass expulsions.Eruptive variables, definition and study. A-Z index of Cognitio.

 

The cataclysmic or explosive variables, which are experiencing dramatic changes in their physical state, as in the case of novae or supernovae.Cataclysmic explosive variable, definition and study. A-Z index of Cognitio.

 

Eclipse, binary stars that, seen from Earth, eclipse each other during their orbital motion.Eclipse binary stars, definition and study. A-Z index of Cognitio.

 

The rotating variables, in which the variability is caused by the rotation of the star on itself. Examples are the stars that have large stains that affect the brightness of the stem, or stars that, due to the high rotation speed, are elliptical.Rotating variables, definition and study. A-Z index of Cognitio.

 

The advent of astronomical photography greatly increased the number of known variable stars, and their names quickly reached Z. We tried to run on patches using doubling: starting from RR, then RS, to ZZ. This too was not enough, and it started from the beginning of the alphabet: AA, AB, up to QZ, having 334 combinations available for each constellation.

Variable star, definition and study. A-Z index of Cognitio.

© ALL RIGHTS RESERVED

 

To open the video  click on the image, good view from your Alessandro Brizzi.



Variable star, definition and study. A-Z index of Cognitio.