Cepheid variables are very bright stars, 500 to 300,000 times larger than the Sun, with short periods of change ranging from 1 to 100 days. These are pulsating variables that expand and shrink considerably in a short time according to a certain pattern. Astronomers can make distance measurements to a Cepheid by measuring the variability of its brightness, making it very valuable to science. In a given constellation, the first variable stars discovered were designated by the letters R to Z, for example R Andromedae. This nomenclature system was developed by Friedrich W. Argelander, who gave the first unnamed variable in a constellation the letter R, the first letter not used by Bayer. For subsequent discoveries, the letters RR to RZ, SS to SZ are used, e.g. RR Lyrae. Later discoveries used the letters AA to AZ, BB to BZ and QQ to QZ (omitting J). Once these 334 combinations are exhausted, the variables are numbered in order of discovery, starting with the V335 prefix upwards. Mira variables are asymptotic giant giants (AGB) red giants. Over periods of several months, they fade and brighten between 2.5 and 11 orders of magnitude, which corresponds to a change in brightness of 6 to 30,000 times.
Mira itself, also known as Omicron Ceti (ο Cet), varies in brightness from almost 2nd magnitude to as faint as 10th magnitude with a period of about 332 days. The very large visual amplitudes are mainly due to the shift of energy production between the visual and infrared when the temperature of the star changes. In some cases, Mira variables show dramatic period changes over a period of several decades, which are thought to be related to the thermal momentum cycle of the most advanced AGB stars. “V1 is the most important star in the history of cosmology,” astronomer Dave Soderblom of the Space Telescope Science Institute (STScI) in Maryland said in a statement. “This is a groundbreaking discovery that has proven that the universe is larger and full of galaxies.” These sample phrases are automatically selected from various online information sources to reflect the current use of the word “variable star”. The views expressed in the examples do not represent the views of Merriam-Webster or its editors. Send us your feedback. These systems have a red giant and a white dwarf in a binary star system. Instead of matter being accreted by gravitational pull as in recurrent novae, in symbiotic systems, matter is ejected from the surface of the red giant due to the stellar wind.
The resulting eruptions when material falls on the white dwarf are less regular and smaller than the other eruptive variables, which brighten up to three orders of magnitude. Examples are R Aquarii and BF Cygni. These symbiotic binary star systems consist of a red giant and a hot blue star surrounded by a cloud of gas and dust. They undergo nova-type eruptions with amplitudes of up to 4 orders of magnitude. The prototype of this class is Z Andromedae. Extrinsic variable stars have variations in brightness due to external factors. Again, there are many different types, but they fall into two main groups: obfuscation binaries and rotating variables. So we have RR Lyrae variables, long-period variables and Mira variables. All of them vary due to internal changes in the stars themselves. The Orion variables are young hot stars of the pre-main sequence that are usually embedded in nebulae. They have irregular periods with amplitudes of several orders of magnitude.
A well-known subtype of Orion variables are the T-Tauri variables. The variability of T Tauri stars is due to spots on the stellar surface and clusters of gas dust orbiting in circumstellar disks. Conclusion: A variable star is a star whose brightness changes regularly. Here we discuss the different types of variable stars and what causes their variations in brightness. The variability of the more massive Herbig Ae/Be stars (2-8 solar masses) is thought to be due to clusters of gas dust orbiting in circumstellar disks. However, if enough mass is collected, such a situation would cause huge thermonuclear explosions that would blow up the white dwarf. They destroy the star, which then becomes known as a Type Ia supernova. When the star is in the source phase, its outer layers expand, which cools them. Due to the drop in temperature, the degree of ionization also decreases. This makes the gas more transparent and allows the star to radiate its energy more easily. This, in turn, causes the star to contract.
When the gas is compressed, it is heated and the degree of ionization increases again. This makes the gas more opaque and the radiation is temporarily trapped in the gas. As a result, the gas is further heated, causing it to expand again. This maintains a cycle of expansion and compression (swelling and shrinkage). [ref. needed] AM CVn variables are symbiotic binary stars in which a white dwarf accretes helium-rich matter from another white dwarf, helium star or evolved main sequence star. They are subject to complex variations or sometimes no variation with ultra-short periods. I had no idea who they were because the Grand Duke was dressed in suits and had no star or jewels to distinguish him. Real Housewives of New Jersey star Teresa Giudice has been sentenced to 15 months in prison for bankruptcy fraud. Betelgeuse has not exploded and its brightness has now returned to normal. Why did it suddenly get dark? Astronomers note that when the internal process of stars like Betelgeuse began to change, the star releases huge clouds of dark dust. Astronomers believe that dust clouds have dimmed Betelgeuse`s light from Earth.
A high amplitude blue pulsator (BLAP) is a pulsating star characterized by changes of 0.2 to 0.4 orders of magnitude with typical periods of 20 to 40 minutes. Cepheid variables are named after the first known example of the type, the star Delta Cephei, discovered as a variable in 1874. Darkened binary stars are stars that pass in front of each other and cause fluctuations and obscure the light seen on Earth. Darkened binary stars can have their own planets, obscuring their light like a lunar eclipse on Earth. One of the most well-known obscured binary stars is Algol. These stars of spectral type A2 to F5, similar δ Scuti variables, are mainly found in globular clusters. They show brightness variations of the order of 0.7 (about 100% change in brightness) approximately every 1 to 2 hours. About two-thirds of all variable stars appear to pulse.  In the 1930s, astronomer Arthur Stanley Eddington showed that mathematical equations describing the interior of a star can lead to instabilities that make a star throb.  The most common type of instability is related to oscillations of the degree of ionization in the outer convective layers of the star.  The processes behind the obfuscation of binary stars are explained in more detail in the section on binary stars. They are also considered variable because the overall luminosity of the system decreases as one of the constituent stars is obscured by the other.
The light curves generated by the occultation of binary systems show striking periodic minima. Extrinsic variables have variations in brightness as seen by terrestrial observers due to an external source. One of the most common reasons is the presence of a binary star, so the two together form a double star. Viewed from certain angles, one star can obscure the other, resulting in a reduction in brightness. One of the most famous occultation binaries is Algol or Beta Persei (β Persei). Cataclysmic variables (also called explosive variables) brighten due to sudden or violent eruptions caused by thermonuclear processes on the surface or deep inside. These include binary stars, with two nearby stars having a mutual effect on mass. Supernovae, novae, recurrent novae and dwarf novae are a group of stars that show dramatic or sudden increases in size, usually due to a stellar explosion. When we look at the night sky, it`s easy to imagine that the stars are immutable. Aside from the brightness of our atmosphere, stars seem firm and constant to the untrained eye. Careful observations, some even with the naked eye, show that some stars appear to change brightness over time.
Some exhibit periodic behavior, brighten quickly, then slowly decrease in brightness, to repeat.