ARTICLE PAGES

ARTICLE : COLOUR in STARS and DOUBLE STARS

The APPLICATION of ADMIRAL SMYTH’s
“SIDEREAL CHROMATICS”

By Andrew James

What are the wild waves saying?

Joseph Edwards Carpenter (1850)

DISCUSSION

The Failure of Smyth’s “Chromatics”

19th Century Understanding of the Nature of Light

Modern solutions for single and double stars and their evolution can be traced back to the works created in Smyth’s day. The immediate significance of double stars was first derived by Sir William Herschel. His initial observations of pairs was to find their numbers, true gravitational connection and comparative motions. Yet the understanding behaviour and origin of light became also the significant hurdle. Prior to Einstein’s Special Theory of Relativity, science thought that different wavelengths of coloured light produced by the stars were primarily caused by the variations in the speed of light.

This was based on the 1842 assumption of Christian Doppler (1803-1853) who explained the colour changes of variable stars being caused by their relative motion towards or away the Earth. Stars therefore moving towards the Earth would be bluer while those that were receding would become redder. However the failure of this postulate was that the colour beyond the red or blue parts of the spectrum was replaced by other light like infra-red, etc., instead of leaving some predicted blackened or missing part of the visible spectrum. It was Hippolyte Fizeau (1819-1896) who realised the consequence of the red or blue shift did not change the colour of the object but did change the relative positions of the spectral lines depending on how fast and the direction of motion towards or away from the observer.

Secondly, physicists and astronomers also had assumed that light was simply propagated and behaved exactly the same way as ocean waves or ripples on a pond. (See Page [*40]) This assumption meant that some kind of transmission medium was required for the waves to pass through the now debunked theory of the æther. If so, then the velocity of light would then be variable depending on the medium. I.e. In air or in water. This is true. However what is not true, was that different wavelengths of light travel at differing velocities.

Ideas regarding the differential velocity of light were not new. Initially first proposed by Isaac Newton, light was postulated that the cause of all the colours of light were travelling at different rates and were inherent to the medium itself. Stellar colour production was therefore problems of the influence of the æther — whose composition, which Smyth then correctly and openly said; “…we are at present profoundly ignorant.”

Smyth wanted to expand this debate to include the Fresnel and Young’s undulating theory [*41]. These scientists, among numerous others, showed that pure colours are just monochromatic light that had just different wavelengths/ frequencies. If the red waves were shorter were compared to the longer blue wavelengths, as Smyth strongly argues, that then blue light must travel faster than longer wavelengths of red light. If one were to look some star some distance away, then emitted starlight meant that the differing emanating star colours would arrive over certain time intervals — perhaps over several weeks. Furthermore. this could also be extended to real motion of the source in space. Assuming the Galilean or Newtonian framework, known as classic physics, then the speed of light was direction dependant. If true, we should see different speeds when travelling in different directions with respect to some moving observer. This was also not true. Such incorrect theories were actually properly dispelled by James Maxwell (1) in his set of equations that were experimentally proven with the famous Michelson-Morley light experiment conducted in 1887. Overall this eliminated the need for the carrier background of the æther. Maxwell’s new understanding of electromagnetism theory finally proved to be the interconnection between electricity and magnetism — so light became known as electro-magnetic radiation or as “waves of light” of varying periods.

Maxwell then further deducing that all kinds of light travelled at similar speed. By 1887 his prediction was vindicated with the detection of radio waves from an electronic circuit and resoundingly confirming the speed of light ‘c’. These ideas were again affirmed by Lorentz in 1900 and by Einstein’s Special Theory of Relativity (1905) — explaining that ‘c’ was an absolute constant. This gave an understanding of both the general behaviour of light and the amount of energy the photons contains.

Interestingly, James Maxwell also had investigated on the physical behaviour of light to enforce his theory. He then formulated the commonly used educational science experiment by combining red, blue and green light to make white light. He also demonstrated the working principle of colour vision in the eye. (Of course, the truly sad thing about all these deliberations is that they occurred around the same time as Smyth’s. He never saw these revelations come to fruition.)

Stellar Evolution Theory in the 19th Century

In the beginning of the 19th Century little was known about the evolution of stars, but as this century passed by, a growing impetus in the subject saw giant steps towards some understanding. In 1800, the stars were still just considered as part of the celestial realm, whose composition and nature were always going to remain hidden from the World. A main key to the discovery of their chemical natures occurred by studying the light from the stars themselves. In 1802, William Wollaston analysing some starlight by passing it through a narrow slit found that the normal coloured spectrum was crossed by numerous dark lines which were not gaps in the stellar spectra.

It was originally assumed that the stars were made in clouds of gas to from red giants. As the star evolved, gravitational forces crushed the body, so that the body slowly changed through the spectrum to end as a smaller bright blue-coloured body before being extinguished as a white dwarf ember — like the companion to the bright star Sirius. Such evolution seemed natural and necessary — mainly to explain the energy source that made the stars shine so brightly. In the mid-1850s interest with double stars were mainly in the real hope of either discovering how heavy the stars were or to sort some evidence of their evolution. The former postulate needed enough evidence for orbital motion, and at the time of Smyth’s writing, only few examples were known. Most prominent of the stars was the southern binary of Alpha Centauri, which is discussed in detail. (See [*39])

In the end, however, the 19th Century advancements were greatly hindered without the familiar instrumental and telescopic means that exist today.

Early 20th Century Theories of Stellar Evolution

One of the first problem in stellar evolution theory is to understand what actually makes the stars shine. In the earliest of times, stars were once commonly thought to be unchanging and eternal. Later it was generally accepted that all stars were actually shining by either by some combustible fire or by celestial friction against the invisible aether. However, these theories were untenable because of the aeons of time that the stars had to have been shining. When further coupled with the substantial fossil and geological evidence and a long-term consistency for the solar radiation, it was shown that any typical combustible energy source was clearly impossible. Soon some elementary calculations easily showed that if the Sun were made of coal then its age would be merely 6,000 years!

Herman von Helmholtz in the 1850s initially proposed the theory that the Sun and stars generated heat by simple contraction. This was conveniently provided by gravity literally squeezing the energy out of the star. Helmholtz proposed that if the Sun shrank by as much as eighty metres per year it would liberate the quantity of energy presently radiated by the Sun. However, if the Sun were to shrink from an infinite size, this period could only be extended to about fifty million years. So this shrinking gravitational theory continued to remain popular until the 1920s, but again these ideas were quite inadequate against real observations.

For many years the true energy source of the Sun or stars remained elusive. Wrongly, early ideas on stellar evolution theory proposed that red giant stars were younger than hot blue stars. Supported by Sir Arthur Eddington in the 1920s, this compression theory further indicated that stars started as red giants or supergiants and went through the entire spectral sequence to finally transform into smaller blue stars to presumably end as white dwarf embers. Yet the early spectroscopic analysis showed that this could not be true, as the red stars had too many metallic spectral lines — certainly an identifying precursor of old age.

A belief in this theory still continued until the late 1940’s. For example, in the 1940 general astronomy text, “A Story of Astronomy” by Draper and Lockwood, which states;

“Until fairly recently… it was generally believed that stars simply evolve simply by loss of heat. The extremely hot bluish-white stars were thought to be the young vigorous members of the star family. These stars after losing some of their heat, so the theory said, passed successively through the increasing cooler stages of yellow and orange-red, down finally to the last oldest and coldest age of all, that of the red stars. This particular evolutionary theory, however has fallen by the wayside, as so many attractive theories must. Astronomers know now that the cooler stars are divided into two classes, the giants and the dwarfs, the dwarfs showing much greater densities than the giants. It seems probable today, as the result of research in this field, that the average stellar body own evolution of the begins with the red giant star, passing with increasing temperature range through the orange-red, yellow and bluish white which shows the maximum temperature of all. Then it is believed that the star’s temperature begins to decline, passing in reverse order back through the yellow, orange-red and red stages, with the corresponding increase in density as the temperature decreases. The end of this sequence brings us to the dense red dwarf stars, and they were considered to be the densest and coolest, and probably the oldest of stars. The next stage after the red dwarf is perhaps oblivion — so far, at least, as any very active radiation is concerned.”

Until Einstein’s energy-mass equivalence or E = mc² equation, where matter can be converted to energy by nuclear fusion, or vice-versa, this concept of red to blue evolution of stars remained fixed as the best theory. Some old texts can be seen to elaborate Helmholtz’ old theory. Today some views of these theories can be enjoyed with some amusement.

Why Were the Colours of Double Stars
A Significant Problem to Smyth?

Smyth in the Sidereal Chromatics argues that all stars should be pure white with the stellar light being a blend of all the colours arriving at different rates. Otherwise, the only other possibility becomes that all stars could be varying significantly in colour — which he used the examples of the colour changes seen in the decreasing brightness of the Tycho supernova seen 1572. It might be also the cause of the presumed change in the colour from ancient times of the brightest star Sirius, R Geminorum[*19], [*20] or the eclipsing variable star Algol (β Persei). Although there appears that these stars do have significant changes in brightness, Smyth then goes on to further argue that some changes in variable stars could be explained by his stellar colour theory.

However, it is quite likely Admiral Smyth was not the originator of this idea, as he states that the French astronomer and physicist François Jean Dominique Arago (1786-1853) who once tried seeing such color changes without much success. This prompts the consideration that other observers before Smyth had thought of similar ideas — but all these failed as real observations could not be made to prove or disprove this overall theory. It is interesting why the astronomers of the day then, described as natural philosophers, persisted with this strange view. It could have been equally argued, for instance, that the colour differences were primarily caused by the stellar surface temperature. Another possibility is changes overtime in the radial velocities of stars. They then could presume that colour variability could also be caused by physical changes in the stars themselves. A classic example are the Cepheid variables. These may change by one or two spectral classes during the regular periodic cycle. I.e. Between G to K spectral class.

Such physical changes in colour made Admiral Smyth think that this was something that was assumably detectable if the human eye was properly trained. Although he then goes on to correctly identify the primary sources of errors; being namely the atmosphere; the altitude of the star above the horizon; the effects on the eye by artificial light sources; and problems with eyepiece achromaticity — yet he surprisingly completely dismisses this serious known problem with refractors, stating it; “… will not affect the difference observed!”

A most innovative idea in this text was to use of a standard colour chart at the eyepiece for observational colour determination (See page [*48]), and this simple idea I have toyed with myself over the years. Prior to examination of star colours by Admiral Smyth, some observers had proposed the use of small coloured jewel-stones and gems as star colour comparisons. Often these were not used — mainly because of their poor range of colour and being too costly to acquire for practicable use. Smyth also proposed the use of water colours placed on white card. These he suggests could be made up by any “chromatic” observer as required, using either paints or various inert inorganic chemicals. Problems with using standardised colour charts is the illumination to view the colour chart itself — and is still problematic. Today, we can control the background illumination readily, but during Smyth’s day the use of candlelight or lamplight means that the illumination would produce a distinct yellowish hue or tint. Smyth eliminated this effect by assuming that these “yellow” stars were colourless but could be separated by some “greyness scale.” I.e. Origin of the grey stars. He summarised the nature of colours under “lamplight” as;

“…very numerous shades from white to pale yellow are so unfit for representation and lamplight reference, that they are omitted in the annexed form; but the careful observer may readily estimate the intensity of almost colourless bodies according to the following order — Creamy white 1, Silvery white 2, Pearl white 3, and Pale white 4.” [*54] and [*55]

Modern Views About Colour

The existence of colour has been known since the dawn of time and has been exploited by both the animal kingdom and humankind ever since. All of the early human civilisations have taken colour essentially as matter-of-fact and it was not until investigation of the optical properties of materials that any scientific progression occurred. One of the earliest attempts was with Isaac Newton who first investigated the breaking up of white-light into the colours of the rainbow. It was Newton’s rainbow colour circle that became the first scientific division of the main colours. These seven colours being violet, blue, green, yellow, orange, red, and indigo.

It has been known and demonstrated from the times of the earliest painters that the use of three basic colour pigments combined with black and white could be used to produce the infinite varieties of hues. Artists used chemical materials or substances, properly called chromatic pigments. These today are now known not to be actually be related to the properties of monochromatic light — colours produced by one single wavelength of light. These painters saw that the primary colours were red, yellow and blue, and were deemed absolute colours because they could not be produced by any other means.

Explaining the nature of the radiation of light, Thomas Young during 1807 first stated these absolute colours were quite different. He said that the primary radiations of the spectrum were red-orange, green and blue-violet. Differences between the painter and the physicist were soon to be brought to some understanding regarding these coloured pigments and light. These we now know as the additive colours and subtractive colours, and something incidentally that was taught to us at very young ages when we all first went to primary school. Consequently, an example of additive colours is when the specified young colours are added together to produce pure white light. If these pigments of the artistic colours are added together, these produce both pure black or these subtractive colours.

These differences of these colour combinations were first explained correctly by Hermann von Helmholtz in 1855. Later the usefulness of these effects was exploited in both photography and commercial printing. Similar principles also worked with colour computer monitors and in colour televisions. In painting and art most colours are usually recognised as achromatic or neutral colours, but whether white or black are really interpreted as “colours” is still open to some debate. Optically, white light should not defined as colour because it comprises as the sum of all the radiations in the visible spectrum. With optical light, including sunlight or starlight, there are no mixtures of black and white. What we are describing in this instance is one montage or blend of monochromatic colour hues. This is far different from the artistic views of the colours seen on Earth. It is important to note that in the physical world cannot be truly or adequately described in the artistic world — therein the major fault with our early ideas about colour that have existed since about the mid-1850s.

As such, in observational astronomy there is no need, therefore, to describe colour sensation and sensitivities in terms of tone, value or purity — or even in lightness or alternatively greyness. These were are adequately described in the much simpler terms of only hue and saturation.

In most terms, saturation is often used in terms of an absolute purity of colour, but this really is an abstract hypothesis. In reality such light finds saturation not as rays of determined wavelength but mixtures of radiations of differing proportions, often signified by the specific wavelength that predominates all the others.

In nature, all observed colour is based on the true colour of the light source, the absorption of light by the chemical composition in the object, and the re-emission of the non-absorbed light. Most stars are, in fact, mainly “unsaturated” due to difficulties seeing colour by the evolutionary contraints or limitations of our human eyes as seen against against the dark background sky.

Last Update : 26th April 2017

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