Star Map

a chart of all or part of the stellar sky. A collection of star maps of contiguous portions of the sky which cover the entire sky or a certain part of it is called a star atlas.

Star maps are used to direct a telescope to the necessary point in the sky, to identify stars in the sky or to match their images on photographs with stars described in star catalogs, to locate objects in the stellar sky (planets, comets, variable stars) by their coordinates, and so forth. They are also used to determine the approximate coordinates of celestial objects (for example, artificial earth satellites during visual observations) by plotting them on maps with a coordinate grid. Most star maps are provided with a coordinate grid in the equatorial system of celestial coordinates (right ascension and declination). General survey star maps are usually compiled separately for the northern and southern skies in stereographic projection. A cylindrical projection is used to depict the equatorial belt of the sky. The polar regions of the sky are depicted in azimuthal projection and the intermediate regions in conic projection. A distinction is made between drawn star maps and photographic star maps. On drawn maps, stars are depicted by small circles of various diameters depending on the brightness of the star and are plotted on the chart in correspondence with stellar coordinates, which are taken from star catalogs. Photographic star maps are made from prints of the stellar sky. Photographic maps are gnomonic projections of the stellar sky and contain more stars than drawn maps.

The oldest known star maps date from the 13th century; star globes were used before this. In 1603 the German astronomer J. Bayer in his star atlas Uranometria denoted the bright stars of each constellation by letters of the Greek alphabet; these designations have been preserved to our day. From the 17th to the 19th centuries atlases appeared by the Polish astronomer J. Hevelius (1690), the British astronomer J. Flamsteed (1729), and the German astronomers J. E. Bode (1782), F. Argelander (1843), and E. Heis (1872). The Atlas of the Northern Sky, which was completed on the basis of the Banner Durchmusterung of the northern sky, compiled by Argelander, and the atlas of the southern sky, compiled on the basis of the Cordoba Durchmusterung, are of great significance for astronomy. The first Russian star map was compiled in 1699 by a decree of Peter I. The following atlases published in the 20th century have found extensive use: the star atlases of the Soviet astronomer A. A. Mikhailov and the Czech astronomer A. Becvarz and the atlas of the entire sky of the Smithsonian Astrophysical Observatory (USA), which is published with a catalog to aid photographic observations of artificial earth satellites.

In 1887 the International Astronomical Congress adopted a resolution for the compilation of the photographic Carte du del. This work was conducted at 21 observatories in different countries and on completion was to give 22,000 sheets of a photographic atlas of the entire sky to a stellar magnitude of 15 (the work remains incomplete). In the USA a photographic atlas was published between 1954 and 1967 by the National Geographic Society and Palomar Observatory. The atlas contains prints made from blue-sensitive plates (limiting magnitude, 21.0) and red-sensitive plates (limiting magnitude, 20.0). The 20th century has seen publication of photographic star maps with degree grids drawn on them. Such are the star maps by the Austrian astronomer J. Palisa, who used the photographs by the German astronomer M. Wolf; the maps of the Royal Astronomical Society (England); and the atlas by the German astronomer H. Vehrenberg.

For an initial acquaintance with the sky, atlases and maps of stars visible only to the naked eye are published.