(ORDO NEWS) — What is a variable star? It’s simple: those stars that change their brightness are called variables.
A star is considered variable if its apparent magnitude, that is, its brightness, changes when viewed from Earth. It does not matter whether these changes take place over several years or take only a fraction of a second. It also doesn’t matter how much the star’s brightness changes.
The difference can range from one thousandth to 20 magnitudes. To date, more than 100 thousand variable stars have been discovered, scientists hypothetically consider about a thousand more stars to be variables.
One of the clearest examples of variable stars is the Sun. During the solar cycle, which lasts 11 years, the energy emitted by the Sun changes by 0.1%, or one thousandth of its value.
History of Variable Stars
The first variable star discovered in modern history was the star Omicron Ceti, later called Mira. In 1596, David Fabricius called her “new star”. More than 4 decades after its discovery, namely in 1638, Johan Holvard discovered that the star is variable, and the period of change in its brightness is 11 months.
This was an extremely important discovery. It helped scientists refute the theory of ancient philosophers who believed that the stars are eternal and unchanging. The discovery of variable stars, as well as data on supernovae, paved the way for the development of astronomy as a science.
In a speech marking the 400th anniversary of Mira’s discovery, Dorrit Hoffleit, a scientist at Yale University, said: “In the 17th century, after Fabricius’s discovery, four more variable stars similar to Mira were discovered.
In all these cases, astronomers suspected that the stars were “new” long before the “official” discovery in the Western world. Three of the four stars were called “new” in early Chinese or Korean annals.”
The second variable star was discovered by Geminiano Montanari in 1669. It was an eclipsing variable star, later named Algol. Although, it is worth noting that the fact that the brightness of this star is changing was discovered by John Goodryk already in 1784. Over the next 80 years, seven more variable stars were discovered.
Since 1850, many variable stars have been discovered. This was facilitated by the development of photography. As of 2008, there were over 46,000 variable stars in the Milky Way Galaxy in the general catalogue.
Characteristics and varieties of variable stars
There are a number of reasons for this variability. The brightness of stars or stellar mass may change, and obstacles may arise that prevent light from reaching the Earth. Pulsating variable stars can expand and contract. In addition, various celestial objects can pass in front of the stars, which is why they appear less bright from the Earth.
Depending on what caused the fluctuation in the brightness of a star (internal physical processes or external factors), scientists divide variable stars into two categories.
The study of variable stars is extremely important for astronomy. They give scientists information about the mass, radius, temperature and luminosity of stars, and also allow a glimpse into the history of their development.
In order to understand the nature of variable stars, it is necessary to systematically observe their behavior over many decades. An important role in this belongs to amateur astronomers. They assist in the collection of information that is entered into the AAVSO International Database.
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