Ian Ridpath’s Star Tales

Chapter One concluded...


By now the age of exploration was well under way and navigator–astronomers turned their attentions to the hitherto uncharted regions of the sky in the southern hemisphere that had been below the horizon for the ancient Greeks. Three names stand out from this era. The first is Petrus Plancius (1552–1622), a Dutch theologian and cartographer; his name is the Latinized form of Pieter Platevoet (literally, Peter Flatfoot). The other two were the Dutch navigators Pieter Dirkszoon Keyser (also known as Petrus Theodorus or Peter Theodore) and Frederick de Houtman. Surprisingly, all three are little-known today despite their lasting contributions.

Plancius instructed Keyser to make observations to fill in the constellation-free zone around the south celestial pole. Keyser was chief pilot on the Hollandia and later on the Mauritius, two of the fleet of four ships that left the Netherlands in 1595 on the first Dutch trading expedition to the East Indies, sailing via Madagascar. Keyser was adept at astronomy and mathematics; the Dutch author A. J. M. Wanders, in his book In the Realm of the Sun and Stars, writes that Keyser observed from the crow’s nest with an instrument given to him by Plancius. Keyser died in September 1596 while the fleet was at Bantam (now Banten, near the modern Serang in western Java). His catalogue of 135 stars, divided into 12 newly invented constellations, was delivered to Plancius when the fleet returned to Holland the following year. Regrettably, little else seems to be known about the life and accomplishments of Keyser, but he left his mark indelibly on the sky.

Keyser’s 12 new constellations first appeared on a globe by Plancius in 1598, and again two years later on a globe by the Dutch cartographer Jodocus Hondius. Their acceptance was assured when Johann Bayer, a German astronomer, included them in his Uranometria of 1603, the leading star atlas of its day. Keyser’s observations were published in tabular form by Johannes Kepler in the Rudolphine Tables of 1627.

The Dutch fleet in which Keyser sailed was commanded by the explorer Cornelis de Houtman; among the crew was his younger brother Frederick de Houtman (1571–1627) who apparently assisted Keyser in his observations. On a second expedition in 1598 Cornelis was killed and Frederick was imprisoned by the Sultan of Atjeh in northern Sumatra. Frederick made good use of his two years in prison by studying the local Malay language and making astronomical observations.

In 1603, following his return to Holland, Frederick de Houtman published his observations as an appendix to a Malayan and Madagascan dictionary that he compiled – one of the most unlikely pieces of astronomical publishing in history. In the Introduction he wrote: ‘Also added are the declinations of many fixed stars around the south pole; never seen before today. Observed and written down by Frederick de Houtman from Gouda.’

De Houtman increased Keyser’s 135 measured star positions to 303, although 107 of these were stars already known to Ptolemy, according to a study of the catalogue by the English astronomer E. B. Knobel. Nowhere did de Houtman give Keyser credit for his priority. De Houtman’s catalogue of southern stars, divided into the same 12 constellations as Keyser’s, was used by the Dutch cartographer Willem Janszoon Blaeu for his celestial globes from 1603 onwards. Keyser and de Houtman are now credited jointly with the invention of these 12 southern constellations, which are still recognized today (see table below).


Twelve constellations introduced 1596–1603 by Pieter Dirkszoon Keyser and Frederick de Houtman

Apus	Chamaeleon	Dorado
Grus	Hydrus	Indus
Musca	Pavo	Phoenix
Triangulum Australe	Tucana	Volans

As the accuracy of astronomical observations improved and fainter stars were charted, the opportunities grew for innovators to introduce new constellations even among the area of sky known to the ancient Greeks. In addition to recording the southern constellations of Keyser and de Houtman, Petrus Plancius invented some constellations of his own, among them Columba, the dove, which he formed from nine stars that Ptolemy had listed as surrounding Canis Major; he also invented the unlikely sounding Monoceros, the unicorn, and Camelopardalis, the giraffe, from faint stars uncharted by Ptolemy. These three Plancius constellations are still accepted by astronomers, but his other inventions fell by the wayside (see Chapter Four).

Eleven more constellations were introduced later in the 17th century by the Polish astronomer Johannes Hevelius (1611–87), filling the remaining gaps in the northern sky. They were illustrated in his star atlas called Firmamentum Sobiescianum, published posthumously in 1690. Oddly enough, Hevelius insisted on observing with the naked eye even though telescopes were by then available; many of his constellations were deliberately faint as though he was boasting of the power of his eyesight. Of Hevelius’s inventions, seven are still accepted by astronomers (see table below). The rejected four were Cerberus, Mons Maenalus, Musca and Triangulum Minor.


Seven constellations introduced by Johannes Hevelius on his star map published posthumously in 1690

Canes Venatici	Lacerta	Leo Minor	Lynx
Scutum	Sextans	Vulpecula

Although the northern constellations were now complete, there were still gaps in the southern sky. These were filled by the French astronomer Nicolas Louis de Lacaille (1713–62) who sailed to South Africa in 1750 and set up a small observatory at Cape Town under the famous Table Mountain, which impressed him so much that he later named a constellation after it, Mensa. At the Cape from August 1751 to July 1752 Lacaille observed the positions of nearly 10,000 stars, an astounding total in the short time.

On his return to France in 1754, Lacaille presented a map of the southern skies to the French Royal Academy of Sciences, including 14 new constellations of his own invention (see table below). The map was published in 1756, and Lacaille’s new constellations were rapidly accepted by other astronomers.

Whereas Keyser and de Houtman had mostly named their constellations after exotic animals, Lacaille commemorated instruments of science and art, with the exception of Mensa, named after the Table Mountain under which he had carried out his observations. His full catalogue, and a revised map, was published under the title Coelum Australe Stelliferum in 1763. In this catalogue, Lacaille divided up the unwieldy constellation Argo Navis, the ship, into the subsections Carina, Puppis and Vela that astronomers still use as separate constellations. As well as creating 14 new constellations, Lacaille eliminated a pre-existing one – Robur Carolinum, Charles’s Oak, introduced by the Englishman Edmond Halley in 1678 to honour King Charles II.


Fourteen constellations introduced by Nicolas Louis de Lacaille in 1754

Antlia	Caelum	Circinus
Fornax	Horologium	Mensa
Microscopium	Norma	Octans
Pictor	Pyxis	Reticulum
Sculptor	Telescopium

All those from Lacaille’s time onwards who gerrymandered with the constellations did so without lasting success, but there were plenty of astronomers who tried to leave their mark on the sky. Constellation mania had reached its height by 1801 when the German astronomer Johann Elert Bode (1747–1826) published his immense star atlas, Uranographia, containing over 100 different constellations; but by then astronomers realized that things had gone too far, and during the ensuing century this number was eroded by a process of natural wastage. In 1899 the American historian R. H. Allen summed up the prevailing situation in his book Star Names and Their Meaning: ‘From 80 to 90 constellations may be considered as now more or less acknowledged’.

One serious deficiency was that there were still no generally agreed boundaries to the constellations. Since Bode’s time cartographers had drawn dotted lines snaking between constellation figures, but these were arbitrary lines of demarcation that varied from atlas to atlas. The matter was settled once and for all by astronomy’s governing body, the International Astronomical Union (IAU).

At its first General Assembly in 1922, the IAU officially adopted the list of 88 constellations, covering the entire sky, that we use today. On behalf of the IAU a Belgian astronomer, Eugène Delporte (1882–1955), then drew up a definitive list of boundaries for these 88 constellations. Delporte’s work, published in 1930 in a book called Délimitation Scientifique des Constellations, amounts to an international treaty on the demarcation of the sky, which astronomers throughout the world have conformed to ever since. Constellations are now regarded not as star patterns but as precisely defined areas of sky, rather like countries on Earth. Unlike the map of the Earth, though, the map of the sky is unlikely to change.




Official boundaries to the constellations were fixed in 1930 by a Belgian astronomer, Eugène Delporte, acting on behalf of the International Astronomical Union. Here is his chart for part of the northern sky, including Cassiopeia and Andromeda. The constellation boundaries follow circles of right ascension (the equivalent of longitude in the sky) and parallels of declination (the celestial equivalent of latitude). (Author’s collection)




© Ian Ridpath. All rights reserved


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