Galaxies are one of the most fascinating phenomena in the universe. The diversity of their forms is an indication of various interaction processes which take place within or between galaxies.
Galaxies can be described abstractly as collections of gas, dust, and stars. However, a look at the astrophysics of galaxies allows one to better understand their morphology. Only shortly after their discovery, the study of the forms and evolution of galaxies led to fundamental questions about the nature of the universe.
THE FIRST GALAXY CATALOGUES
One of the early telescopic observers was Charles Messier, who catalogued the first galaxies in the second half of the eighteenth century. His motivation was to avoid confusing these specks of light with new comets. The first edition of the Messier catalogue was published in 1774 and extended in 1780 and 1781. In the Messier catalogue, there was no classification of nebulae according to their appearance. The first galaxy in the Messier catalogue is M 31, the Andromeda Galaxy. In the original catalogue, Messier describes M 31 as “the beautiful nebula in the belt of Andromeda, in the form of a spindle, similar to two opposite cones or pyramids whose bases touch”. The galaxies M 32 and M 33 follow in the catalogue. M 32 is described as a “small, round nebula” and one reads about M 33 that “the nebula is of white light which is almost uniform, but somewhat brighter at two-thirds of its diameter”. These prosaic texts describe the objects, but do not allow a comparison or classification since such descriptions depend on the individual impressions at the telescope and the size of the instrument.
A further pioneer in the observations of galaxies was Friedrich Wilhelm Herschel (known as William Herschel after his emigration to England) who, aided by his sister Caroline, actively looked for further such nebulae and star clusters. Their observations led to several catalogues of “new Nebulæ, nebulous Stars, planetary Nebulæ, and Clusters of Stars” which were published in 1786, 1789, and 1802. William Herschel writes in the preface to his third catalogue that “our stock of materials is now so increased, that we should begin to arrange them more scientifically”.