Siriusly Red - By Rens Van Der Sluijs

Posted by ProjectC 
By Rens Van Der Sluijs
Aug 14, 2009

<i>Sirius A and its faint companion, Sirius B. Credit: Hubble Space Telescope/NASA/ESA,
H. Bond (STScI) and M. Barstow (University of Leicester).</i></center>

As has often been pointed out, by definition the uniformitarian creed precludes the very real possibility of rare and radical changes in nature.

Since the late 19th century, most geologists have fondly embraced the adage of the British lawyer and geologist, Sir Charles Lyell (1797-1875): ‘The present is the key to the past.’ Its naïve implication is that all phenomena that ever happened in nature still occur today and can be observed. Historical evidence is valuable precisely because it offers an even better key to the past than present-day analogues: eye-witness accounts.

A prime application of the historical method concerns the colour of Sirius A or &#945; Canis Majoris, the brightest star in the night sky. Sirius appears bright white today, but – as the English amateur astronomer, Thomas Barker (1722-1809), first pointed out in 1760 – was emphatically qualified as red in many classical texts. Poetical passages aside, Seneca commented that Sirius was of a deeper red than Mars, while Ptolemy labeled the star “reddish” and grouped it with five other stars, all of which are indeed of red or orange aspect.

Even as late as the 6th century CE, the Gallo-Roman chronicler, Gregory of Tours, could label the Dog Star rubeola or ‘reddish’. It is claimed that the earliest unambiguous reference to Sirius as a white star is found in the pages of the Persian astronomer, ‘Abd al-Ra&#7717;man al-Suf&#299; (903-986 CE).

What to make of all this? The paradox has sparked a prolonged and fairly intense debate, which has led to a fair number of publications, including Noah Brosch’s recent book Sirius Matters (2008). The evasive explanation that Sirius’s red traced to a simple textual error is easily refuted by the eminent authority of Ptolemy and Seneca as well as the observation that the same attribution is attested in a number of other cultures. For example, the Pawnee, of the North American Plains, associated each of the four intercardinal points with a colour, a type of weather, an animal, a tree, and a star.

The southeastern corner was the domain of red, the “Red Star” – which might be the planet Mars – and the wolf, explicitly linked to Sirius. Another suggestion, that an optical illusion accounts for the confusion, seems merely a red herring. It may be so that the star, to the unaided eye, often appears to be flashing with red, white and blue hues when near the horizon, but such scintillations would not have deluded such a skilled observer as Ptolemy. The belief in a red Sirius was clearly genuine. But how can it be reconciled with the white hue seen today?

Two Canadian archaeoastronomers, David Kelley and Eugene Milone, followed a rather more promising direction: “We conclude that the bulk of the evidence supports a literal red Sirius interpretation … Thus, the discovery that the bright star, Sirius, was once described as red, when it is now clearly white, may light up formerly obscure paths of stellar evolution.” The trouble is that, on the current astronomical model of stellar evolution, no shift from red to white is possible over such a short time.

In 1985, the German astronomers, Wolfhard Schlosser and Werner Bergmann, concluded that Sirius B, the faint binary companion of Sirius A, had been a red giant in Antiquity. If correct, there must indeed be some hitherto “obscure paths” of stellar behaviour. With some exasperation, Kelley & Milone posed the questions: “Are there any instances in which stars have undergone shorter time scale changes than evolutionary time scales would require? … How then could it have been a red giant only 2000 years ago? … How reliable are the reports of a color change? … Are we interpreting the reports correctly?”

It is not that scholars have not tried. Remaining faithful to the accepted model of stellar change, Kelley & Milone experimented with the idea that a diffusion of hydrogen from the top layer into a lower layer of carbon inside the star could have triggered “a thermonuclear runaway … that would lead to a retracing of the star’s evolution back through the red giant branch, and making the star that became Sirius B to appear as much as 100 times more luminous than Sirius A.” While such a ‘red’ state could in theory be sustained for “hundreds of years”, a “major impediment” is “a 100:1 brightness ratio of a red giant to Sirius A”, which “would make it brighter than Venus at that planet’s impressive maximum, but its brightness is recorded by Ptolemy, and there is no evidence for any great change in the overall brightness of the Sirius system.” This obstacle effectively falsifies the idea.

A second thought-experiment is that the circumstellar matter moving from one star to the other may occasionally dim its companion “and thus the system as a whole, as well as redden it.” The objection here is the lack of evidence that any such nebulosity has taken place in recent times.

All of this should have raised a red flag for the validity of the thermonuclear model of stellar evolution. Before the development of this model, and of the so-called Hertzsprung-Russell diagram, in the early 20th century, scientists had no compunction to speculate that stars may occasionally change in brightness – as novae do – as well as in hue.

In fact, the answer must allow for recurrent fluctuations, as a white colour for Sirius has occasionally been reported in earlier times. The renowned Chinese historian, S&#299;m&#259; Qi&#257;n (±140-86 BCE), produced an astrological statement to that effect: “When the Wolf changes colour, there will be much piracy and theft.” His western colleague, Hephaestio of Thebes (4th century CE), allowed for a clear variation: “… if Sirius rises bright and white and its appearance shines through, then the Nile will rise high and there will be abundance, but if it rises fiery and reddish there will be war”. Manilius and Avienus, meanwhile, reported a ‘sea-blue’ colour for the star.

If the behaviour of stars is controlled electrically, the puzzle receives an almost instant solution. In his book The Electric Sky, the American electrical engineer, Donald Scott, offers a masterful refutation of the accepted theory of stellar evolution. A list of counter-examples of this theory includes Sirius. On the substitute ‘electric star model’, the behaviour of stars as “balls of electric plasma” is determined by the intensity of electrical input. Repeated changes could have resulted in nova-like fluctuations in colour and brightness, which may have ended in a binary pair resulting from fissioning. Clearly, the entrenched idea that stars are fueled by nuclear fusion and evolve in a uniformitarian manner can no longer be taken as read.

Contributed by Rens Van Der Sluijs