A variable star is a star whose brightness as seen from Earth fluctuates. This variation may be caused by a change in emitted light or by something blocking the light, so variable stars are classified as either: Intrinsic variables, whose luminosity changes. Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth. Many most, stars have at least some variation in luminosity: the energy output of our Sun, for example, varies by about 0.1% over an 11-year solar cycle. An ancient Egyptian calendar of lucky and unlucky days composed some 3,200 years ago may be the oldest preserved historical document of the discovery of a variable star, the eclipsing binary Algol. Of the modern astronomers, the first variable star was identified in 1638 when Johannes Holwarda noticed that Omicron Ceti pulsated in a cycle taking 11 months; this discovery, combined with supernovae observed in 1572 and 1604, proved that the starry sky was not eternally invariable as Aristotle and other ancient philosophers had taught.
In this way, the discovery of variable stars contributed to the astronomical revolution of the sixteenth and early seventeenth centuries. The second variable star to be described was the eclipsing variable Algol, by Geminiano Montanari in 1669. Chi Cygni was identified in 1686 by G. Kirch R Hydrae in 1704 by G. D. Maraldi. By 1786 ten variable stars were known. John Goodricke himself discovered Beta Lyrae. Since 1850 the number of known variable stars has increased especially after 1890 when it became possible to identify variable stars by means of photography; the latest edition of the General Catalogue of Variable Stars lists more than 46,000 variable stars in the Milky Way, as well as 10,000 in other galaxies, over 10,000'suspected' variables. The most common kinds of variability involve changes in brightness, but other types of variability occur, in particular changes in the spectrum. By combining light curve data with observed spectral changes, astronomers are able to explain why a particular star is variable.
Variable stars are analysed using photometry, spectrophotometry and spectroscopy. Measurements of their changes in brightness can be plotted to produce light curves. For regular variables, the period of variation and its amplitude can be well established. Peak brightnesses in the light curve are known as maxima. Amateur astronomers can do useful scientific study of variable stars by visually comparing the star with other stars within the same telescopic field of view of which the magnitudes are known and constant. By estimating the variable's magnitude and noting the time of observation a visual lightcurve can be constructed; the American Association of Variable Star Observers collects such observations from participants around the world and shares the data with the scientific community. From the light curve the following data are derived: are the brightness variations periodical, irregular, or unique? What is the period of the brightness fluctuations? What is the shape of the light curve? From the spectrum the following data are derived: what kind of star is it: what is its temperature, its luminosity class? is it a single star, or a binary? does the spectrum change with time?
Changes in brightness may depend on the part of the spectrum, observed if the wavelengths of spectral lines are shifted this points to movements strong magnetic fields on the star betray themselves in the spectrum abnormal emission or absorption lines may be indication of a hot stellar atmosphere, or gas clouds surrounding the star. In few cases it is possible to make pictures of a stellar disk; these may show darker spots on its surface. Combining light curves with spectral data gives a clue as to the changes that occur in a variable star. For example, evidence for a pulsating star is found in its shifting spectrum because its surface periodically moves toward and away from us, with the same frequency as its changing brightness. About two-thirds of all variable stars appear to be pulsating. In the 1930s astronomer Arthur Stanley Eddington showed that the mathematical equations that describe the interior of a star may lead to instabilities that cause a star to pulsate; the most common type of instability is related to oscillations in the degree of ionization in outer, convective layers of the star.
Suppose the star is in the swelling phase. Its outer layers expand; because of the decreasing temperature the degree of ionization decreases. This makes the gas more transparent, thus makes it easier for the star to radiate its energy; this in turn will make the star start to contract. As the gas is thereby compressed, it is heated and the degree of ionization again increases. Thi
Russian Academy of Sciences
The Russian Academy of Sciences consists of the national academy of Russia. Headquartered in Moscow, the Academy is considered a civil, self-governed, non-commercial organization chartered by the Government of Russia, it combines scientists employed by institutions. Near the central academy building there is a monument to Yuri Gagarin in the square bearing his name; as of November 2017, the Academy included other units. There are three types of membership in the RAS: full members, corresponding members, foreign members. Academicians and corresponding members must be citizens of the Russian Federation. However, some academicians and corresponding members were elected before the collapse of the USSR and are now citizens of other countries. Members of RAS are elected based on their scientific contributions – election to membership is considered prestigious. In the years 2005–2012, the academy had 500 full and 700 corresponding members, but in 2013, after the Russian Academy of Agricultural Sciences and the Russian Academy of Medical Sciences became incorporated into the RAS, a number of the RAS members accordingly increased.
The last elections to the renewed Russian Academy of Sciences were organized in October 2016. In the beginning of April 2019, the Academy had 460 foreign members. Since 2015, the Academy awards, on a competitive basis, the honorary scientific rank of a RAS Professor to the top-level researchers with Russian citizenship. Now there are 605 scientists with this rank. RAS professorship is not a membership type but its holders are considered as possible candidates for membership; the RAS consists of 13 specialized scientific divisions, three territorial branches and 15 regional scientific centers. The Academy has numerous councils and commissions, all organized for different purposes. Siberian Branch of the Russian Academy of Sciences The Siberian Branch was established in 1957, with Mikhail Lavrentyev as founding chairman. Research centers are in Novosibirsk, Krasnoyarsk, Yakutsk, Ulan-Ude, Kemerovo and Omsk; as of end-2017, the Branch employed over 12,500 scientific researchers, 211 of whom were members of the Academy.
Ural Branch of the Russian Academy of Sciences The Ural Branch was established in 1932, with Aleksandr Fersman as its founding chairman. Research centers are in Yekaterinburg, Cheliabinsk, Orenburg and Syktyvkar; as of 2016, 112 Ural scientists were members of the Academy. Far East Branch of the Russian Academy of Sciences The Far East Branch includes the Primorsky Scientific Center in Vladivostok, the Amur Scientific Center in Blagoveschensk, the Khabarovsk Scientific Center, the Sakhalin Scientific Center in Yuzhno-Sakhalinsk, the Kamchatka Scientific Center in Petropavlovsk-Kamchatsky, the North-Eastern Scientific Center in Magadan, the Far East Regional Agriculture Center in Ussuriysk and several Medical institutions; as of 2017, there were 64 Academy members in the Branch. Kazan Scientific Center Pushchino Scientific Center Samara Scientific Center Saratov Scientific Center Vladikavkaz Scientific Center of the RAS and the Government of the Republic Alania- Northern Ossetia Dagestan Scientific Center Kabardino-Balkarian Scientific Center Karelian Research Centre of RAS Kola Scientific Center Nizhny Novgorod Center Science Scientific of the RAS in Chernogolovka St. Petersburg Scientific Center Ufa Scientific Center Southern Scientific Center Troitsk Scientific Center The Russian Academy of Sciences comprises a large number of research institutions, including: Member institutions are linked via a dedicated Russian Space Science Internet.
Started with just three members, The RSSI now has 3,100 members, including 57 from the largest research institutions. Russian universities and technical institutes are not under the supervision of the RAS, but a number of leading universities, such as Moscow State University, St. Petersburg State University, Novosibirsk State University, the Moscow Institute of Physics and Technology, make use of the staff and facilities of many institutes of the RAS. From 1933 to 1992, the main scientific journal of the Soviet Academy of Sciences was the Proceedings of the USSR Academy of Sciences; the Academy is increasing its presence in the educational area. In 1990 the Higher Chemical College of the Russian Academy of Sciences was founded, a specialized university intended to provide extensive opportunities for students to choose an academic path; the Academy gives out a number of different prizes and awards among which: The Emperor Peter the Great and advised by Gottfried Leibniz, founded the Academy in Saint Petersburg.
Called The Saint Petersburg Academy of Sciences (Russian
The Milky Way is the galaxy that contains our Solar System. The name describes the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye; the term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος. From Earth, the Milky Way appears as a band. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610; until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies; the Milky Way is a barred spiral galaxy with a diameter between 200,000 light-years. It is estimated to contain 100 -- more than 100 billion planets; the Solar System is located at a radius of 26,490 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust.
The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The galactic center is an intense radio source known as Sagittarius A*, assumed to be a supermassive black hole of 4.100 million solar masses. Stars and gases at a wide range of distances from the Galactic Center orbit at 220 kilometers per second; the constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way is invisible to telescopes, neither emitting nor absorbing electromagnetic radiation. This conjectural mass has been termed "dark matter"; the rotational period is about 240 million years at the radius of the Sun. The Milky Way as a whole is moving at a velocity of 600 km per second with respect to extragalactic frames of reference; the oldest stars in the Milky Way are nearly as old as the Universe itself and thus formed shortly after the Dark Ages of the Big Bang. The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, itself a component of the Laniakea Supercluster.
The Milky Way is visible from Earth as a hazy band of white light, some 30° wide, arching across the night sky. In night sky observing, although all the individual naked-eye stars in the entire sky are part of the Milky Way, the term “Milky Way” is limited to this band of light; the light originates from the accumulation of unresolved stars and other material located in the direction of the galactic plane. Dark regions within the band, such as the Great Rift and the Coalsack, are areas where interstellar dust blocks light from distant stars; the area of sky that the Milky Way obscures is called the Zone of Avoidance. The Milky Way has a low surface brightness, its visibility can be reduced by background light, such as light pollution or moonlight. The sky needs to be darker than about 20.2 magnitude per square arcsecond in order for the Milky Way to be visible. It should be visible if the limiting magnitude is +5.1 or better and shows a great deal of detail at +6.1. This makes the Milky Way difficult to see from brightly lit urban or suburban areas, but prominent when viewed from rural areas when the Moon is below the horizon.
Maps of artificial night sky brightness show that more than one-third of Earth's population cannot see the Milky Way from their homes due to light pollution. As viewed from Earth, the visible region of the Milky Way's galactic plane occupies an area of the sky that includes 30 constellations; the Galactic Center lies in the direction of Sagittarius. From Sagittarius, the hazy band of white light appears to pass around to the galactic anticenter in Auriga; the band continues the rest of the way around the sky, back to Sagittarius, dividing the sky into two equal hemispheres. The galactic plane is inclined by about 60° to the ecliptic. Relative to the celestial equator, it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic, relative to the galactic plane; the north galactic pole is situated at right ascension 12h 49m, declination +27.4° near β Comae Berenices, the south galactic pole is near α Sculptoris.
Because of this high inclination, depending on the time of night and year, the arch of the Milky Way may appear low or high in the sky. For observers from latitudes 65° north to 65° south, the Milky Way passes directly overhead twice a day; the Milky Way is the second-largest galaxy in the Local Group, with its stellar disk 100,000 ly in diameter and, on average 1,000 ly thick. The Milky Way is 1.5 trillion times the mass of the Sun. To compare the relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US quarter, the Milky Way would be the size of the contiguous United States. There is a ring-like filament of stars rippling above and below the flat galactic plane, wrapping around the Milky Way at a diameter of 150,000–180,000 light-years, which may be part of the Milky Way itself. Estimates of the mass of the Milky Way vary, depending upon the method and data used; the low end of the estimate range is 5.8×1011 solar masses, somewhat less than that of the Andromeda Galaxy.
Measurements using the Very Long Baseline Array in 2009 found