According to theory, the universe originated with such an explosive force that presently the farthest galaxies are hurling away at nearly the speed of light.Today, the light astronomers see from the most distant galaxies origi-nated when the universe was less than one-fifth its present age.The begin-ning universe did not grow at a steady rate but might have suddenly expanded temporarily by a process called inflation. During this time, gravity might have briefly become a repulsive force rather than one of attraction, causing the cosmos to undergo a tremendous spurt of growth. The infant universe rapidly ballooned outward for an instant and then settled down to a more constant rate of expansion as it progressed to the more conventional type of development observed today.The inflation theory explains some of the universe’s fundamental features, such as the uniformity of the microwave afterglow of the big bang and the apparent lack of curvature, or flatness, of space. This great firestorm lasted about 100,000 years and involved practically all matter in the universe. Huge swirling masses of high-temperature plasma composed of elementary particles flew outward into space in all directions. Currents and eddies flowed violently through this primordial soup, forcing material to clump together.The temperature of the protouniverse eventually cooled sufficiently to allow the formation of protons and neutrons, which came together into atomic nuclei. At some point following the big bang, fluctuations in the smooth flow of matter and energy served as seeds for galaxy formation.A change in the fabric of space produced lumps and ripples in the distribution of matter.These yielded galaxies and galaxy clusters with up to hundreds of members.This phase transition apparently occurred during the first million years or so of the universe’s life after electrons had combined with protons to produce hydrogen atoms, the starting materials of the universe.Hydrogen and helium comprise more than 99 percent of all matter in the universe. Helium is continuously being generated in the stars. However, hydrogen was made only once, at the beginning of the universe, and no new hydrogen has been created since the big bang.
The universe is estimated to be composed of about 75 percent hydrogen, 25 percent helium, and minor amounts of other elements. A puzzling question concerning the universe is this abundance of helium.The gas is made up of a nucleus of two protons and two neutrons orbited by two electrons. It is observed on the surface of the Sun and was actually discovered on the Sun before it was found on Earth. Helium exists in the stars of this galaxy, in the stars of other galaxies, and in interstellar space. The nuclear fusion reactions that power the stars and convert hydrogen into helium can account for only a minor percentage of the helium.Therefore, the bulk of the helium must have originated during the big bang.As the protouniverse continued to expand, the basic units of matter began to agglomerate into some 50 billion galaxies, each with tens of billions or hundreds of billions of stars.The universe is dominated by small- to medium-sized stars with less than 80 percent of the mass of the Sun. Remnants of the big bang can still be found by measuring the temperature of the universe. Besides starlight, the universe radiates other forms of energy.One of these is microwave radiation spread evenly throughout the universe. Its discovery in the mid-1960s was instrumental in the development of the big bang theory.This leftover energy from the creation of the universe has presently cooled to within a few degrees above absolute zero (–273 degrees Celsius), the temperature at which all molecular motion ceases. Faint temperature fluctuations in the background microwave radiation might signify primordial lumps that later gave rise to the present-day galaxies.
The galaxies are arranged in four basic types: elliptical, spiral, irregular, and diffuse.The elliptical galaxies are quite old and spheroidal in shape, with the highest light intensity at their centers. Fully formed elliptical galaxies, which took shape over a period of 1 billion years, already existed when the universe was only one-tenth its current age, when spiral galaxies were still forming. Powerful radio sources originate most often from elliptical galaxies. Their red color suggests that these galaxies contain an abundance of old stars. A spiral galaxy (Fig. 3),which includes the Milky Way, has a pronounced bulge at its center, much like a mini-elliptical galaxy. A spiral-patterned disk populated with young stars surrounds this bulge. The spiral arms generate magnetic fields produced by the rotation of the galaxy. Irregular galaxies, as their name implies, have many shapes and are relatively low in mass. Diffuse galaxies have low surface brightness with more gas and much less of a spiral structure, suggesting they are not fully developed. The age of the universe is determined by measuring the distance and speed of the farthest known galaxies some 15 billion light-years from Earth by using the red shift of their starlight.The color of light emitted by stars shifts to the longer wavelengths, or the red end of the electromagnetic spectrum (Fig. 4),when the star is moving away.The farthest galaxies therefore have the largest red shifts, signifying they are traveling the fastest. A paradox seems to exist, however, because the universe appears to be younger than its oldest stars due to uncertainties about the value of the Hubble constant used for measur-
ing the rate of expansion of the universe. Astronomers glimpse back toward the very beginning of the universe by observing an apparent massive protogalaxy in its formative stages. It is 12 billion light-years from Earth, meaning the object was seen as it existed only a few billion years after the big bang. In the meantime, the Milky Way galaxy (Fig. 5),which is of fairly modest size, pulled enough matter together to form a large spiral galaxy, similar to many others observed in the far reaches of space.The Milky Way contains some 100 billion stars spread out across a dis-
tance of about 100,000 light-years. Astronomers can also weigh the universe to determine whether it will continue to expand, collapse upon itself into a dense cosmic soup, or remain in a steady state, with new galaxies forming to fill the voids created by the expansion.The weight of the universe signifies its gravitational attraction. It can be determined by measuring the mass of an average galaxy and multiplying that number by the total number of galaxies. Yet more matter appears to exist than that observed in the visible universe. This is known as the missing mass.This unseen dark matter might be many times more massive than all the stars combined and could contain up to 90 percent of all the mass in the universe. Moreover, the supposed dark matter in the Milky Way’s halo, a large region that extends well beyond the galaxy’s visible outline, is what holds the rapidly rotating galaxy together.At least half this missing mat- ter could reside in ordinary dead stars called white dwarfs, objects as small as Earth but 1 million times denser.Without large amounts of hidden mass, the galaxy would simply fly apart. Furthermore, not knowing how much mass is missing means that the ending of the universe, whether it expands forever or collapses in on itself, will remain a perplexing enigma.
В тёмное время суток и безлунную ночь на небе вспыхивают сотни и тысячи звезд. Яркость и блеск индивидуальность каждой звезде, это связанно с разницей в расстояниях между ними, и в разнице их
действительной светимостью. Для обозначения яркости звезд (видемой) есть имерения шкалой называемых видимых звездных величин. Деление шкалы в одну звездную единицу есть , одна из звезд ярче другой приблизительно в 2.5 раза (точнее в 2.512 раза). И для различия звёзд между собой их принято обьединять в группу - созвездия. 
