{"id":26208,"date":"2021-11-18T11:28:55","date_gmt":"2021-11-18T11:28:55","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=26208"},"modified":"2021-11-18T11:28:55","modified_gmt":"2021-11-18T11:28:55","slug":"who-let-the-dogs-out","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2021\/11\/18\/who-let-the-dogs-out\/","title":{"rendered":"Who let the dogs out?"},"content":{"rendered":"\n

The origin of Canes Venatici, the Hunting Dogs, can be traced to the 17th century, but who deserves credit? Ian Ridpath picks up the scent<\/p>\n\n

\"\"
A modern-day representation of Canes Venatici, the Hunting Dogs, from the popular planetarium program Stellarium. The constellation is best seen from after midnight to before dawn this month<\/figcaption><\/figure>\n\n
\"\"
Two lone stars just below the tail of Ursa Major, the Great Bear, in this 1515 star chart by Albrecht D\u00fcrer would later become part of the constellation of Canes Venatici, the Hunting dogs \u2013 as defined by Johannes Hevelius <\/figcaption><\/figure><\/div>\n\n

Two dogs snap at the heels of the Ursa Major, the Great Bear, in a nightly chase around the north celestial pole. These canines are the hunting hounds of Bo\u00f6tes, the Herdsman, who holds them on a leash in his outstretched hand. In Greek tradition, Bo\u00f6tes was visualised in several ways, usually herding or driving animals. One story says that the name Bo\u00f6tes comes from the Greek for ox driver, since the stars of the Plough were visualised as an ox cart. An alternative explanation is that the name comes from a Greek word meaning \u2019noisy\u2019, and we can perhaps imagine the sounds of the herdsman shouting to his animals in the night.<\/p>\n\n

The two dogs of Bo\u00f6tes are represented by the constellation of Canes Venatici, but this isn\u2019t one of the 48 figures that the ancient Greek astronomer Ptolemy listed in his great source book, the Almagest, <\/em>written around 150 AD.<\/p>\n\n

Unlike the modern constellations, which fit neatly together, the Greek constellations didn\u2019t fill the entire sky. Between Bo\u00f6tes and Ursa Major was a large gap. Within it were two stars, which Ptolemy had classed among the \u2018unformed\u2019 stars outside Ursa Major, not part of any constellation and so free to use in a new figure. You can see this gap, and the two stars, on old charts of the Ptolemaic constellations such as the one by Albrecht D\u00fcrer (see below).<\/p>\n\n

The brighter member of this pair of stars is known as Cor Caroli (Alpha (\u03b1) Canum Venaticorum) or \u2018Charles\u2019s Heart\u2019, a name given to it by British astronomers in the 17th century, before Canes Venatici was formed. How this name came about is a story in itself.<\/p>\n\n

\"\"
Johannes Hevelius (left) clashed with the Royal Society\u2019s Robert Hooke (right) about the use of instruments with telescopic sights <\/figcaption><\/figure><\/div>\n\n

The prime mover behind the introduction of the constellation of Canes Venatici, the Hunting Dogs, to the sky was Johannes Hevelius (1611\u201387), a wealthy brewer from Danzig, (now Gda\u0144sk, Poland), who was one of the greatest observers of his age. He used his wealth to create a rooftop observatory equipped with top-quality instruments of his own construction. His interests were wideranging and his output prolific: he observed sunspots, comets and the variable star Mira (Omicron (\u03bf) Ceti) \u2013 which he named, plus a transit of Mercury, the moons of Jupiter and the rings of Saturn. He also produced the first atlas of the Moon, Selenographia. <\/em>Like his hero Tycho Brahe (1546\u20131601), Hevelius published his results on his own printing press.<\/p>\n\n

The underlying aim for much of his life, though, was to improve on Tycho\u2019s catalogue of a thousand stars. Had he wished, Hevelius could have produced the first-ever star catalogue made with a telescope, ahead of John Flamsteed at Greenwich, but he was concerned that lenses might introduce positional distortions. Instead, he relied on simple naked-eye sighting instruments, such as sextants and quadrants similar to those used by Brahe in pre-telescopic days. Hevelius claimed that their quality and his sharp eyesight were a match for smaller instruments with telescopic sights.<\/p>\n\n

Royal Society, which had elected him as a of ale, so the two got on famously and, upon his return, Halley was happy to endorse the accuracy of Hevelius\u2019s results. Subsequent analysis has shown This brought Hevelius into conflict with the member in 1664. Robert Hooke, in particular, doubted that his results would be a match for telescopic measurements, but Hevelius disagreed. To resolve the issue, Edmond Halley went to visit Hevelius and observed alongside him using a quadrant with telescopic sights.<\/p>\n\n

Hevelius was a brewer and Halley liked a glass that his star positions were indeed more accurate than Brahe\u2019s.<\/p>\n\n

The Catalogus <\/em>Stellarum <\/em>Fixarum <\/em>(\u2018Catalogue of Fixed Stars\u2019) by Hevelius contained over 1,500 stars, 50 per cent more than either Ptolemy or Brahe had recorded, giving him plenty of raw material from which to fashion new constellations in the gaps between the ancient figures. The catalogue was in the process of being printed in 1687 when Hevelius died. It was seen through to publication by his wife Elisabeth, eventually appearing in 1690 along with a magnificent atlas, Firmamentum <\/em>Sobiescianum, <\/em>named in honour of the Polish king, John III Sobieski.<\/p>\n\n

\"\"
After naming the constellation of Canes Venatici, the Hunting Dogs, Hevelius depicted them as greyhounds in his Firmamentum Sobiescianum star atlas, published posthumously in 1690<\/figcaption><\/figure><\/div>\n\n
Long-lasting appeal<\/strong><\/h5>\n\n

Along with the Ptolemaic figures, the catalogue and atlas of Hevelius contained 10 constellations of his own devising, seven of which we still use today: Canes Venatici, the Hunting Dogs; Lacerta, the Lizard; Leo Minor, the Smaller Lion; Lynx; Scutum, the Shield; Sextans, the Sextant; and Vulpecula, the Little Fox.<\/p>\n\n

The depiction of Canes Venatici by Hevelius can be seen in his 1690 atlas (pictured above). As on all of his charts, the constellation is drawn as it would appear on a globe, so it appears back-to-front compared to the way we see it in the sky. The dogs are meant to be greyhounds, which hunt as a pair, although they might not look like it the way they\u2019re drawn on some charts. Hevelius named the northern dog Asterion and the southern one Chara (he deemed them to be male and female respectively).<\/p>\n\n

Chara, leading the chase, is clearly the top dog as she contains the two unformed stars listed by Ptolemy, of third and fourth magnitude, now known as Alpha (\u03b1) Canum Venaticorum and Beta (\u03b2) Canum Venaticorum. These designations were allocated by the English astronomer Francis Baily in his Catalogue <\/em>of <\/em>Stars <\/em>of <\/em>the <\/em>British <\/em>Association <\/em>for <\/em>the <\/em>Advancement <\/em>of <\/em>Science <\/em>of 1845, since Hevelius didn\u2019t use Greek letters on his charts. Alpha (\u03b1) Canum Venaticorum is Cor Caroli. By contrast, Chara\u2019s kennel-mate Asterion is marked by only a scattering of faint stars.<\/p>\n\n

Although Hevelius is rightly credited with the invention of the constellation of Canes Venatici, he was not the first to show dogs in this area. That honour goes to the German astronomer Peter Apian (Petrus Apianus in Latin) who published a star chart showing Bo\u00f6tes with two dogs in 1533 (pictured above, top), 150 years before Hevelius. Three years later, on another of Apian\u2019s charts, the number of dogs had grown to three (pictured above).<\/p>\n\n