1. Definitions for the primary parameters of colour are hue, saturation and brightness. This is where hue is the dominant — just as Wiens law dictates for the observed colours of stars. In brief the definitions are;

Hue is the discernible colour based on the dependant dominate wavelength, independent saturation or brightness.

Saturation is the observed degree of whiteness added to the colour.

Brightness is the observed intensity of the visible light from a source.

2. The subject of colour and its nature is known in science of physics as radiometry, and is specifically directed to the measurement of electromagnetic radiation and light — including the visible portion of the electromagnetic spectrum. Such measurements, especially in astronomy, are made using photometry, which measures and expresses light in terms of radiation units of the source, like energy (in S.I. units of Watts), and radiance and irradiance — being power (watts) per unit area (I.e. S.I. units of square metre (m2) or in units of solid angles, steradians (sr).

UNITS : Brightness is measured in the SI units known as lux (lx), as the number of lumens per square metre, which in astronomical terms is about 0.25 lux for Full Moon, 1 mlx (milli-lux) for the dark moonless night sky, or 50 to 80μlx for general starlight.

The unit of lumens (lm) is more complicated, being the amount of light (number of photons) emitted by some uniform source of one candela, that is spread over the solid angle of one steradian (sr)

The S.I. unit of the candela (cd) is also the measure of luminosity intensity of some monochromatic light source (single colour). Very few astronomical sources are known to be monochromatic sources.

3. The title of much of the earlier section on green stars I have updated, which first appeared in the 33-doubles e-group entitled Its Not Easy Being Green.

I commented ; In regards the colour Green, perhaps Kermit the Frog is the only being, in this world, who sees these green coloured stars with certainty? (Hence the title…)

4. Ive been thinking of proposing an experiment using several series of stars in increasing Right Ascension, in which the observer has to estimate the apparent colours, and this is later then correlated with the B−V values. This will give an estimate of the ability of the observers to see colours at night, and even shades of those colours. It would also test the colour acuity of the observer, objectively. Would anyone really be interested in such visual experiments?

5. I have some Double Star Colour Estimate results of the seventy-two stars observed by some thirty-two (32) amateurs of the Astronomical Society of New South Wales Inc. with some other nearby Australian astronomical Societies. We conducted these, equally among several northern and many southern pairs. (See the page Notes on Double Stars – Colour Estimates)

6. Luis Arguelles (33-Doubles Communication) commenting on this suggests;

…as commented by other members of the list, probably it was caused from different cultural roles between males and females. I also think its more the question of brain processing of light than the number of cells in our retinas.

7. Ric Hill (33-Doubles Communication Message 835: 05th April 2000), was the one who inspired some of the text above. However, there is absolutely no evidence to support his quote below;

Yes, I remember reading that during WWII a study was conducted by DOD [U.S. Department of Defense], to determine which were better suited for night watch duty. I cant remember the source, possibly Science News but if it was then it was from the early 1990s, or maybe the late 1980s. Basically, it found that women see colour at a lower light level than men but men can see in an overall lower light level than women but its all black and white to us. So if you want to see faint galaxies, be a guy. But if you want to see colour in the Orion Nebula, be a gal. Sorry bout that folks, nature is sexist.

8. I have studied Chemistry and worked for a biscuit company for some sixteen years before leaving several years ago. During 1989, one of my projects was to the set-up for the instrumental measurement of the colour of baked biscuits. I was already fairly interested in colorimetry sometime before this, and actually once did a specific course on colour including colour matching and design. Yet of the seventeen in the class I was the only male, mainly because they designed the course for advertising, textiles, cosmetics and fashion. A small portion however was left under architectural design, which I enjoyed the most, but I unfortunately missed a few of these lectures. Much of the earlier work presented was on colour measurement (colorimetry) and on the creation and nature of pigments. Once I completed the course, I am now considered a colourist, though over the years I have never called myself this. This is mainly because others have often interpreted the negative connotations of the title, presumably me being able to improving there lives by advising matching certain colours to their personalities — the astrology of the colourist. This knowledge, however, has proved to have certain amusing advantages especially with the opposite sex. I.e. Drumming up a conversation, but I have observed, despite my continued advice, most of them still take absolutely no notice — and in some ways I dont blame them! Furthermore, I still continue to wear the standard issue black trousers with brightly coloured tops and jumpers — and never as the current and costly fashion dictates. Oh, and to answer the often general question about my favourite colour — it is pale aqua blue. I find it most calming!


1. Malin, David; The Colours of the Galaxies, Pub. Cambridge University (1996)
2. Colour, Art and Science. Ed. Trevor Lamb and Janine Bourriau, Cambridge University Press. (1995)

a. Baylor, Denis; Colour Mechanisms of the Eye;
b. Millon, John; Seeing Colour
c. Lyons, John; Colour in Language

3. Gerstner, K.;The Forms of Colour-The Interaction of Visual Elements.; MIT Press (1986)


I would like to sincerely thank Tom Teague, Luis Arguelles, Eddy OConner and Raffaello Braga for their poignant views and for being the true inspiration for this text on these pages. However, Richard Harshaw deserves special credit for some really interesting ideas and innovative solutions regarding the colours seen in doubles. One or two ideas by Richard have show pure genius and have forced me to again question for some time on how to apply these to stellar observations.

Note: All of the above are members of the unique 33-doubles Yahoo! Group.


Last Update : 4th August 2012

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