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)
INTRODUCTION
Admiral William Henry Smyth (1788-1865) was the gentleman
amateur astronomer who was born on the 21st January 1788, being only
five days before Captain Arthur Phillip founded the first Australian
Colony of New South Wales under the British Crown. Although born at
Westminster in England, his family had originated from the American
state of Virginia, whose father’s
great fortune mostly vanished during the American War of
Independence as he had strongly supported the losing British
side.
Smyth early maritime, then naval career, began at a very young
age when he joined a merchant ship under the command of experienced
ship’s Master who was employed by the
Royal Navy. He proved to be a very capable and diligent student, and
soon quickly gained his commission and into active service between
1809 and 1813. He rose through the ranks as Lieutenant in March
1813, Commander in September 1815, and then to full Captain in 1817
at only twenty-nine years of age. This last commission here
started after Smyth was posted on the ship H.M.S. Adventure,
whose assigned, voyage was to make the improved survey, with
suitable nautical charts, of the south-eastern and central parts of
the Mediterranean. This mostly included all of the coastlines of
Italy and Sicily, undertaken mostly for trading ships and for
accurate charts to be used during times of war. This same ship had
carried all the necessary astronomical equipment to do accurate
land-based positional observations, including an altitude measuring
9-inch quintant, being a specialised type of sextant. Another
was a 15-inch altitude and azimuth circle. Smyth proved to be most
diligent and proficient for the task, whose final finished work
along with suitable maps, being later published in 1824.
This new navigational survey also gave Captain Smyth the
important opportunity to explore the cosmopolitan cultures around
the Mediterranean during the times of the Napoleonic wars. Early
during 1815, in, Naples, he had met and married Eliza Anne ‘Annarella’
Warington (1788-1873). Already quite talented, Eliza was to
eventually become centrally involved as the assistant to his latter
written works and reductions, including his now most well known
book, the “Cycle of Celestial
Objects” or just “The Cycle” in 1844. Although Smyth’s main training was involved specifically
to astronomical positioning, navigation and seamanship, his general
interest in amateur astronomy was likely sparked during 1817 when he
met the Sicilian astronomer, Giuseppe Piazzi (1746-1826),
while visiting his observatory at Palermo in northern Sicily. After
1825, Smyth withdrew from his more active Naval duties, but remained
an advisor and British Naval Officer. He later achieved the rank of
Admiral in 1863 just prior to his final retirement at the age of
seventy-seven years old.
Admiral W. Smyth had become far more serious about his astronomy
after about 1825, upon moving to the small town of Bedford, some
one hundred kilometres north of London. Here he started his first
series of visual astronomical observations from own his private
observatory — producing the now acclaimed Bedford
Catalogue of deep-sky objects and double stars. In 1839, this
observatory was dismantled and then transfer it to Cardiff. The main
telescope was sold to Dr. Lee, but then re-erected it again at the
Hartwell House and placed in a new observatory designed by Admiral
Smyth. Smyth did on occasions still use this instrument, as his
residence at St.John’s Lodge was not
too far away. After settling in, he again produced another new
series of visual astronomical observations between about 1839 to
1859.
One of his famous sons, Charles Piazzi Smyth (1819-1900)
also became a renown astronomer and artist. Although born in the
Italian city of Naples, Charles Smyth had spent most of his early
adult years at the Cape of Good Hope between 1835 and 1845. He then
returned to Scotland as that country’s
Astronomer-Royal. (“Charles Piazzi
Smyth, astronomer-artist : his Cape years 1835-1845.”; Cape Town (1983) by the southern
astronomical historian Brian Warner.) Charles Smyth had strongly
influenced his father regarding his stellar colour experiments,
culminating with publishing of the last major work of his father
— the “Sidereal
Chromatics.” From his own point of
view, it is likely the nature of star colours influence extended
from father to son, especially with the genuine artistic talents,
but also in having a much wider astronomical knowledge and
experience.
Admiral Smyth was later to become the President of the Royal
Astronomical Society in 1849/50 and did contribute various papers on
diverse subjects that appeared in several Journals between 1829 and
1849. Observationally, the principal telescope was his Tully 15 cm.
(5.9-inch) refractor at his home at ‘Hartwell’ in
Bedford. This same telescope was sold to his friend, Dr. John Lee
— the same person the initial that the letter used in the
introduction, and was recorded in the beginning of the “Chromatics”
We also know it was still in use by him sometime after 1865.
Admiral Smyth eventually died at his home in Cardiff from heart
problems in the early morning of 9th September 1863. He was aged 78
years old.
Works of Admiral Smyth
Admiral W.H. Smyth’s four
main astronomical works included;
A Cycle Of Celestial Objects [1844]
Aedes (or Ædes) Hartwellianae or [1851]
Speculum Hartiwellianum [1860]
Sidereal Chromatics [1864]
The Cycle of Celestial Objects (1844)
One of his best known witing among his astronomical works was the
“The Cycle of Celestial Objects
” published in two large volumes in
1844. This particular work was awarded by the Royal Astronomical
Society with its prodigious Gold Medal. These well researched
volumes proved very popular among amateur observers. This work was
again republished in 1986 by Willman-Bell as the “The Bedford Catalogue” formatted as seen in the original 1844
edition. It is still available as just a single volume book. This
tome is the modern-day originator of many of the common
observational texts on the general appearance of deep-sky objects
and double stars as seen through small to moderate apertures.
Sidereal Chromatics (1864)
One of the first significant astronomical documents on double
star colours was “Sidereal
Chromatics: Colours of Multiple Stars”, often now just named the “Sidereal Chromatics”, beng written as his last book in 1864,
almost a year before his death. This interesting work was based on
several false premises — centred mainly on the nature and
velocity of light through space and the true origins of colour. This
means that much of the scientific background was both misplaced or
just simply wrong. However, in essence it is an obvious development
of astronomical works of Admiral Smyth and of his exploratory voyage
regarding the visual double stars observations of star colours. One
of his interesting methodologies employ in the paper was the
demonstrative rough “colour
blind-tests” on double stars, which
included several noted double star observers, amateurs astronomers,
but also of Smyth’s associates and
friends — and even their wives.
In the scheme of things, much of the text has now been placed as
only casual interesting. Yet it does contain some very interesting
discussions and ideas on the visual interpretation of the nature of
double and multiple star colours. During the years after this tome
was written, several other papers were published on double star
colours in the astronomical literature. These latter papers were
eventually to be replaced in the early part of the 20th Century with
the advent of instrumental photometry and of colour measures like
the Johnston B−V colour scale. This latter measure was to soon
produce the first Colour-Magnitude Diagrams of the bright open star
clusters — leaving the first toe-hold into stellar evolution
theory. After this, serious visual observations of colour
immediately became obsolete and unnecessary.
His interest in the colour of double stars and astronomy
culminated with the Sidereal Chromatics, some of which appears in
the more rudimentary form of the “Bedford Cycle of Celestial
Objects” first published in 1844,
followed by the “Aedes
Hartwellianae” in 1851 and the
“Speculum Hartwellianum” or “Hartwell Cycle” in 1860. When “Speculum Hartwellianum” was originally published in early 1860, it
caused some reaction from the astronomical Smyth community.
One such response was by S.M. Drach as an “Letter to the Editor” on the 12th March 1860 (M.N.R.A.S.,
251 (1860)). This letter discusses an observational device
called the Saussure Cyanometer, which uses colour cards
attached to binocular eyepiece. This presumably would eradicate the
need for;
“…the
conflicting opinions of simultaneous observers on the same night of
double stars…” After
Admiral Smyth’s death, Sidney B.
Kincaid in the next year (1866) published on abstract “On the Estimations of Star
Colours”, MNRAS.,
27, 264-266 (1866) on the question of the possibility that
stars could be variable in colour over short periods. Smyth had
already concluded regarding the double star 95 Herculis, that;
“…no crucial
example of the change in colour of a star has been determined ;
although there is every reason to believe that such objects vary as
well in their hues as in their apparent brilliancies.”
Biographies
Various biographies about Admiral Smyth do exist.
Some of these on the Internet are worthy to read for those
interested in more about the man. I.e. [1]
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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