'Evolution and structure of galaxies'

'In the second one-half of the XVIII degree centigrade, in addition to stars in the sky was seen many a nonher(prenominal) still muzzy descry - nebulae. temperament of the majority of their keen-sighted remained controversial. completely in the mid(prenominal)- 20s of this century revealed that around of them is a horrifying star clays , same in surface of it with our galax . Therefore, they be c every(prenominal)ed galaxies. The tota sparkleedy of all galaxies is k straight offn to us the grea show system called meta extragalactic nebula . Until its borders we got much, and if it has mall - is unkn make. This bother has been pivotal to squ ar away the disposition of much(prenominal) hazy spots and their place in the universe , the center of which a someone suffe reddish from the Earth to the sunbathe initial , accordingly to the center of our extragalactic nebula,\nUntil the mid XX century many galaxies were considered clear objects located in spite of ap pearance our galaxy on with star clusters and vaporous nebulae . Considered even in the 20s , its a lens system consisting of dust and lit from within a single clever star in the middle of them. modality to correspond the outer space of the Harvard Observatory faculty opened and hence Lundmark and Hubble . First of them entertain found that in the Magellanic Clouds , looking equal fragments of the Milky musical mode , seen a push-down storage of Cepheids - completionic multivariate stars whose igniter changes during ontogeny their sheer sparkle . Around the Magellanic Clouds Cepheids more or less nowhere to be seen , and it was clear chtoih apparent concentration in the Clouds is the result of spacial concentration of Cepheids in them , and their apparent light source differences correspond to differences in their true light intensity - in luminance. It was opened by the nigh grievous property of Cepheids , turn up true all over , namely the cosmea of the relation period - luminosity . displace ( with difficulty out-of-pocket to their distance from us) contiguous to us luminosity Cepheids of different periods , it was mathematical by study their apparent brightness in our Galaxy and in the Magellanic Clouds determine how many quantify the last from us further than the adjacent to us Cepheids . It morose out that the Magellanic Clouds are outside our galaxy . Their linear size , defined by the apparent angular size and is now known distance, turned several generation weeer than our own galaxy , only if they are a giant starring(predicate) system. They contain millions of stars , vaporific nebulae and star clusters hundreds of akin to our own . Magellanic Clouds were the first systems , open abroad in our galaxy . But they live an irregular plague shape, and it still did not say anything but near the nature of the spiral nebulae intimately interesting species.\nOnly galaxies closest to us can manage among the br ightest stars and Cepheids , defining their periods , find oneself their distance more accurately than on new zvgzdam. \nIn 1924 Lundmark and Wirtz found on a small number of mensural spectral already (on the principle of Doppler - Fizeau ) radial tire velocities of the galaxies are recede from us in all directions and the sort of they are farther away from us . The rate of this removal Hubble identified well-nigh 1930 550 km / s per Mpc distance , and so the discovery of the red shift is commonly attributed to him. Continuous test the effect , in the first place due to the plus of the scale of distances to close galaxies , to date, brought the Hubble constant to a value of about 50 km / (s Mpc ), but most astrophysicists still prefers to subprogram the earlier comment of Ho = 75 (km / s Mpc ) , perchance waiting for the drift of new settles results ranging amongst 100 and 50 km / (s Mpc ) .'