A sky atlas is the counterpart to a topographic map – without it, we would find it very difficult to navigate an unknown terrain or sky. Since the beginnings of astronomy several thousand years ago, many attempts have been made to depict the night sky as accurately as possible. With the rapid progress of astrophotography in the twentieth century, photographic atlases have become available that provide a more natural view of large-scale star clouds and gas nebulae than hand-drawn (or even computer-generated) maps. Well-known examples are the Palomar Observatory Sky Survey and Hans Vehrenberg's Falkau Atlas and Atlas Stellarum.

In the past two decades, astrophotography has been revolutionized by the availability of large-format CCD cameras, which have a vastly higher quantum efficiency than photographic plates and film. As a result, images taken with a CCD camera and a standard 50 mm lens reach almost the same limiting magnitude (14m) as the venerable Atlas Stellarum. The present atlas is the result of state-of-the-art digital image acquisition and processing techniques, combining more than 3000 individual photographs into a uniquely detailed view of the night sky. Axel Mellinger did all the imaging and computer processing, while Ronald Stoyan identified and labeled the stars and deep sky objects.

We would like to thank all those who contributed to the success of this project.

This photographic star atlas shows the entire sky on 82 charts. The chart arrangement is shown on the endpapers, and a schematic depiction is given on page 9. The scale at the center of each field is 1° per cm (2.54° per inch) for all charts. Stars are shown down to approximately 14th magnitude.

Each two-page spread shows the original color image, as well as an inverted and labeled black and white copy. Brightness and contrast were individually optimized for each chart. Hence, charts of regions far from the Milky Way may show slightly fainter stars than those showing rich star fields inside the Milky Way. For printing, the original RGB files had to be converted to the CMYK color space, a process that in some cases may yield slight color shifts compared to the original image.

In order to emphasize extended faint emission nebulae, the inverted maps were created from the red channel images only. For this reason, the brightness of individual stars may differ from their appearance on the color images (red stars appear brighter on the black and white charts, green and blue stars fainter).

The star atlas lists 1593 deep sky objects, all of which can be identified on the photographs. Object designators are based on the catalog of the Eye & Telescope v3.0 software [Pfl2011], which features one of the best error-corrected object databases. In a few cases, these designators may differ from those found in non-corrected catalogs or planetarium software.

At the heart of this atlas is a huge panoramic image of the night sky. To capture the entire night sky, astrophotographer and physics professor Axel Mellinger traveled to remote, dark sites in South Africa, Texas, and the Huron-Manistee National Forest in Michigan. This is the story of how the panorama was created.

The plan

Taking a photograph of the entire night sky is no easy undertaking, and requires careful planning. The first important choice was for a suitable digital camera. In astrophotography, where long exposure times are required, the sensor chip must be cooled to temperatures of -20°C or less in order to keep the dark current low. After comparing several CCD cameras on the market, the SBIG STL-11000 was selected as the best compromise between sensor size and cost.

Its Kodak KA1-11002 chip has the same size as 35 mm film, i.e. 36 mm × 24 mm. It uses microlenses to enhance its quantum efficiency by directing light to the active pixel areas. The camera was fitted with a Minolta MD 1.4/50 mm lens, originally used on a 35 mm format film-based single-lens reflex camera. To improve the image quality, the lens was stopped down to f/4 for all exposures. The chosen combination of focal length and chip size resulted in a 40° × 27° field of view, i.e. 1080 square degrees. Since the sky has a total area of 41,253 square degrees, a complete all-sky panorama requires at least 38 fields.

The night sky of the pretelescopic era was a decidedly uncomplicated place. The heavens contained the fixed stars, the luminous band of the Milky Way, the moon and the five wanderers or planets, all known since before recorded history. Occasionally a brilliant comet swept across the sky; there were also shooting stars which appeared and disappeared in the blink of an eye. And very rarely, a brilliant ‘guest star’ would appear where no star had shone before and then slowly fade over the following months, disturbing the otherwise immutable starry vault.

Beyond this were a handful of cloudy spots in the sky, nature unknown, but like the stars they did not move and so could not be atmospheric phenomena. There was the hazy cloud of stars in the tail of Leo, named Coma Berenices, and the compressed grouping of tiny stars known as the Pleiades. There was a hazy patch of light in the Cassiopeia Milky Way which would one day be known as the Double Cluster. And finally there was the luminous patch in Cancer called the Praesepe.

By the time that William Herschel embarked on his career in astronomy, the telescope had been in use for over 160 years. Progress in improvement and refinement of the instrument had been painfully slow, however, with a combination of factors responsible for the circumstance.

The primary problem with the refractor telescopes of the seventeenth and eighteenth century was spherical and chromatic aberration, a result of the fact that these were single lens instruments that could not overcome their inherent faults. The solution that was found was to increase the focal lengths of the instruments. Where the simple Galilean telescopes of the mid-seventeenth century had apertures of under 2 inches and focal lengths of 2 or 3 feet, instrument makers found that increasing the focal lengths by a factor of 5 or 10 times helped reduce the effects of the aberrations, though they were not nearly eliminated. Over the course of the succeeding decades, astronomers began using telescopes with focal lengths of well over 100 feet and in some cases over 200 feet. Not surprisingly, these were clumsy and cumbersome instruments to use; it was difficult enough aiming the telescope at a selected object, let alone following the object across the sky for any length of time. It was only in the mid-eighteenth century when the first achromatic telescopes were developed that the long refractor telescopes passed into history.

On the occasion of William herschel’s election to the Royal Society on 7 December 1781, his friend William Watson presented him with a copy of Charles Messier’s ‘Catalogue of nebulae and star clusters’, the now famous list of 103 objects which appeared in the Connaissance des Temps for 1784.

At the time, Herschel was preparing to embark on his third survey of the heavens. The first, carried out in the years before 1779, was a survey of all stars of magnitude 4 or brighter, examined with a 7-foot reflector of 4.5-inch aperture. The second survey had begun in August 1779, and was an examination of all stars brighter than magnitude 8 with a 7-foot reflector of 6.2-inch aperture. The primary result of that survey was the compilation of a catalogue of double and multiple stars, numbering 269 in all, which was due to be published in the Royal Society’s Philosophical Transactions early in 1782. An unexpected byproduct of the survey had been Herschel’s discovery of the planet Uranus, the event which transformed Herschel into a professional astronomer of world renown.