Petrus Apianus’s planisphere of 1540

This close-up of the area around Ursa Major comes from Petrus Apianus’s chart of the northern sky in his book Astronomicum Caesareum of 1540.[note] The constellation figures are based on those in Albrecht Dürer’s planisphere of 1515. Whereas Dürer had labelled the stars on his chart with numbers in the order they were listed in Ptolemy’s catalogue, Apianus dropped the numbers and instead introduced a variety of names, some of which we still use. Several of the names were of Arabic origin, as seen here in the tail and body of the Great Bear, garnered from the Book of the Fixed Stars by the tenth-century Persian astronomer bd al-Ramān al-ūfī.

Among the stars named by Apianus was the faint companion to the second star in the Bear’s tail. Ptolemy had not mentioned this companion star, and it was not shown on Dürer’s chart, but it was known to the Arabs as al-suhā, meaning the forgotten or neglected one. Apianus added it as a small dot and labelled it alkor (without a capital). He had first shown it under the name Alcor on a diagram of the north polar region in his Cosmographicus Liber of 1524, and that is the spelling we now use. According to the star name expert Paul Kunitzsch, Apianus’s name for it is a corrupted form of the Arabic al-jaun, which actually refers to the next star along the tail, here named Alioth. Despite Apianus’s error, his name for the star has stuck.

Other names shown by Apianus were Latin, such as Cervix (neck) and Dorsum (back) above the figure of Leo. These were seemingly his own invention, but they were not adopted by other astronomers and we now know these stars as Algieba and Zosma (Gamma and Delta Leonis).

At the top of the image is the pole star, labelled Stella Polaris, its name in Latin, and Alrukaba, an Arabic word meaning ‘the knee’; this name originally applied to θ (theta) in the Great Bear but somehow became wrongly transferred to Polaris.

The dogs of Boötes, and a rose

Note also that Boötes, at right of picture, holds three dogs on a leash, rather than the two that were introduced by Johannes Hevelius as the constellation Canes Venatici half a century later. Ptolemy in the Almagest had said nothing about dogs in this area, and they are not mentioned in any myth. So where did Apianus get the idea for these canine companions?

The star name expert Paul Kunitzsch concluded that it resulted from the misreading of an Arabic manuscript of the Almagest when it was translated into Latin by Gerard of Cremona in the 12th century. According to Kunitzsch, Gerard mistook the Arabic word al-kullāb, referring to the shepherd’s crook carried by Boötes, for al-kilāb, which means dogs, and wrote canes (Latin for dogs) in his translation. Taking Gerard’s word for it, Apianus showed Boötes with two dogs at his heel on a chart in his book Horoscopion Generale of 1533 and added a third for good measure in his charts of 1536 and 1540, as shown at the top of this page. (The modern Canes Venatici, incidentally, occupies the space between Boötes and Ursa Major and incorporates the two stars shown here as open circles beneath the tail of the Great Bear.)

Next to the dogs is a flowerlike symbol labelled Rosa, positioned where Ptolemy had listed the third member of a triangle of stars above the tail of Leo. Ptolemy added to this star the curious description ‘shaped like an ivy leaf’. This description was probably intended to refer to the general appearance of the whole trio and the star cluster within it, now known as Melotte 111. Apianus seemingly tried to turn Ptolemy’s ivy leaf into a rose. This area is now part of the constellation Coma Berenices, which was invented by Apianus’s contemporary Caspar Vopel.

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Star names on the Apianus planisphere of 1540