A star atlas or sky atlas is a collection of star maps that show the entire star sky or a larger area of it. In contrast to geographical atlases, it is always a projection of the celestial sphere and mostly on a uniform scale.
The purpose of these works is - as with individual star maps - multiple:
- the comparison with the visually observed or the photographed starry sky
- the identification of stars or other celestial objects
- the determination of changes in the starry sky ( novae or variable stars , small planets passing through , changes in shape of gas nebulae , etc.)
- the determination of celestial coordinates of drawn objects
- the planning of observation campaigns .
With the first star maps, the star locations were often only drawn in freehand according to the view of the sky, at best based on simple angle measurements. Exact map projections are used as a basis from around the 18th century, with the coordinates mostly coming from surveys , photographic recordings or star catalogs .
The map series show the brightness of the individual stars through signatures of various sizes, often also a graticule . If a star atlas is mainly used for amateur astronomy or to hold guided tours at public observatories , it usually also contains the constellations .
Well-known star atlases
- a sky atlas 1603, Uranometria by Johann Bayer . For the first time it contained the stars of both hemispheres and the system still used today to designate the stars with Greek and Latin letters ( Bayer designation ).
- a sky atlas 1690, also Firmamentum Sobiescianum , by Johannes Hevelius
- a celestial atlas 1750, also Uranographia Britannica , by John Bevis
- a sky atlas 1801 by Johann Elert Bode