The Fabled Zodiacal Light

Both of the photos of the zodiacal light taken near the Very Large Telescope at Paranal capture what it looked like here in the Kalahari. Both images credit ESO (Image credit: ESO Yuri Beletsky — *This photo of the zodiacal light taken at Paranal captures what it looked like here in the Kalahari. Image credit ESO/Yuri Beletsky*

28 March 2019

I can think of few things better than ending a night’s observing by sitting back with a cup of tea and gazing at one of the most remarkable and rarely-seen phenomena of the solar system – sunlight reflecting off comet and asteroid dust concentrated in the plane of the Solar System.

The dark moonless March mornings in the Kalahari offered prime prospects for observing the zodiacal light. And in the pre-dawn sky this morning it was the most dumbfounding display of all: a huge, tapering pyramid of light stretching up almost 50° into the heavens; its core glowing brightly enough to extinguish many of the fainter stars within it.

Its colour was fabulous and quite unlike any colour one otherwise sees – a pearly silver shimmer, gossamer and ethereal. Quite extraordinarily beautiful.

Sitting out there, gazing at the fabled light and thinking what a terrible thing it is that owing to light pollution most observers have never seen it, I was suddenly struck by a very great mystery that has puzzled me ever since:

Where are all the historical references pertaining to it?

In ancient times the unpolluted skies ought to have produced at the very least a frequent mention of this ghostly pyramid of light, if not entire anthologies of myths, fables and folklores.

*This gorgeous photo of the zodiacal light rising above a sea of clouds was taken at ESO’s La Silla Observatory in Chile. Image credit ESO/Y. Beletsky*

It was one of the most extraordinary sights in my morning sky; incredibly bright and incredibly enormous – comparable in its luminosity to the less-bright areas of the Milky Way, albeit a strangely translucent luminosity – and very mysterious in its giant pyramid shape. There are a plethora of references and mythologies attached to the glowing Milky Way – how come no mention of what must have been a very conspicuous and mysterious light in the dark skies of earlier civilisations?

And surely, because it follows the same broad band of the sky as the constellations of the zodiac, its ghostly appearance at spring and autumn had great meaning for those ancient stargazing civilisations that placed great emphasis on the goings on in that region of the sky? One would imagine that as an omen-bearing apparition it would have rivalled comets.

Yet there is no mention of it. And there are no popular names for it in any language, except for the twelfth century Persian astronomer poet, Omar Khayyám who, in his magnificent Rubáiyát made reference to a mysterious ‘false dawn’. Indeed, he must have had a fabulous view of the zodiacal light over the Persian desert for it was worth celebrating with wine:

When false dawn streaks the east with cold, grey line,
Pour in your cups the pure blood of the vine;
The truth, they say, tastes bitter in the mouth,
This is a token that the ‘Truth’ is wine.

The rest is silence.

Until the seventeenth century.

The first description of the zodiacal light occurs in Joshua Childrey’s Britannia Baconia, or the Natural Rarities of England, Scotland and Whales (sic) in 1660. Childrey (1623–1670) was an English churchman and academic, antiquary and astrologer, the archdeacon of Salisbury from 1664 – and his book is significant for containing the first known reference to the beautiful phenomenon of zodiacal light:

“There is another thing, which I recommend to the observation of mathematical men: which is that in February, and for a little before and a little after that month (as I have observed several years together) about six in the evening when the twilight hath almost deserted the horizon, you shall see a plainly discernible way of the twilight striking up towards the Pleiades, and seeming almost to touch them. But what the cause of it should be I cannot yet imagine, but leave it to future enquiry.”

LADEE ZL — *Surely the most extraordinary image of the zodiacal light – as seen from the moon, captured by NASA’s LADEE spacecraft on April 12, 2014*

That ‘future enquiry’ was made by Giovanni Domenico Cassini in 1683 who is credited with ‘discovering’ the zodiacal light. He was the first to investigate it, quantify it, chart it in the celestial sphere and with great insight suggest an explanation for the phenomenon – he and his student, Nicolas Fatio de Duillier, suggested that the source of the zodiacal light was dust particles in orbit around the Sun.

The fact that these four men were the only ones in history to document this beautifully ethereal, ghostly, almost insubstantial phenomenon in our night skies is very, very odd.

It seems to be a puzzle with no possibility of a solution.

For me, the only answer is to bootleg Winston Churchill’s eloquent description of Russia and consider it to be “a riddle, wrapped in a mystery, inside an enigma.”