What are star charts, and how they’ve developed through the centuries?

A star chart reflects the position of stars and constellations on the map of the sky. It also often shows the star brightness, which is represented by signatures. Scientists define star brightness in terms of apparent magnitude, which means how bright does the particular star appear from Earth. A related set of star charts depicting the entire starry sky is called a star atlas. Older atlases are partially confined to the north starry sky. It is thanks to many great scientists and astronomers that we can create a custom star chart for any location on the planet.

 

Early representations of the starry sky

The oldest recognized representation of whole constellations is the ancient Egyptian figure placed in the tomb of Senenmut. On earlier representations of the stars, e.g., As the Nebra Sky Disc, the stars (with the exception of a group that probably represents the Pleiades) were probably randomly distributed by the artist. Apart from mural paintings, there are also known celestial globes and planispheres from antiquity, some of which were used for ornament as well as for astronomical work.

 

The development of maps goes hand in hand with the creation of star catalogs. Ptolemy describes both the construction of celestial globes and planispheres (rotatable star charts). Planispheres have not survived, but Carolingian transcriptions of the Aratos constellation contain planets and representations of individual constellations that were presumably copied from ancient designs. These maps show only the constellations, not the individual stars. From the 9th century, there are more representations of the constellations, especially as part of copies of the Hyginus’ Poeticon Astronomicon. The book describes 47 of the 48 Ptolemaic constellations, focusing on the Greek and Roman mythology surrounding the constellations, though some discussion of the relative positions of stars is included.

 

Historical star charts

Woodcut by Albrecht Dürer 1515. The figure of the northern starry sky shows the twelve zodiac signs in twelve circular sections, and in the corners, the four famous astronomers; Aratus Cilix, Ptolemeus Aegpteus, M. Manilius Romanus, and Azophi Arabus. The four astronomers represent four great traditions of astronomy: Aratus represents the Greek, Ptolemy the Egyptian, Al-Sufi the Islamic, and Marcus Manilius the Roman.

 

The woodcuts depict the northern skies known to European astronomers at the time, and with great skill combines the accuracy of the stars with constellation figures as visualized by the Greeks and Romans. For a long time, almost only maps of the individual constellations were published, whose positions usually refer to the old Greek data of Ptolemy and Hipparchus (whose catalog was lost in the early Middle Ages in the West), if they were not even drawn by hand. Although Ptolemy’s catalog was preserved in the Arab world and Byzantium, it was not until the measurements of astronomers like Tycho Brahe that modern positions were available, which quickly became the standard.

In 1515, the first printed planets of Albrecht Dürer, Johannes Stabius, and Conrad Heinfogel appeared on two maps, showing the entire sky: the hemispheres north and south of the ecliptic.

In 1603, Johann Bayer finally published Uranometria, the first atlas of the entire sky instead of a collection of selected constellations or less accurate planisphere. The positions in Uranometria are based on Tycho Brahe’s observations, who was famous for its observational accuracy. However, the individual maps are still tailored in size to the illustrated constellations so that there is no uniform scale.

However, the actual representation of the sky continued to develop both scientifically and artistically until the Uranographia of J. E. Bode appeared in 1801. The atlas consisted of 20 maps in the format 103 cm × 70 cm and is, therefore, still the largest atlas till date. The engravings are very filigree and rich in detail and show about 17,000 objects of the fixed starry sky. As a result of this abundance, one increasingly came away from figuratively representing the constellations and limited itself to the drawn connecting lines of the main stars. Even the latter appear today only in popular science maps.

 

Today’s star charts

Map of the Night Sky: Star Positions from the Bright Stars Catalog, 5th Edition, are nowadays being used professionally only for limited purposes, but are very popular amongst astronomy fans. Otherwise, either only the catalogs are published, from which one can print sections as needed, or photographic maps that arise directly from telescopic images, such as the Digitized Sky Survey. It is also worth mentioning that many people today use astronomical planetarium software, which often includes extensive star catalogs.

 

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