Eclipses down the ages

The apparent rising and setting of the sun and the Northern Lights are amongst the most captivating natural sights one can enjoy with the naked eye – it almost matches the joy of looking at a smiling human baby. Countless poets and artists immortalised their rapture at witnessing these natural phenomena.

But how people reacted to eclipses is a different story: as the sun or the moon inexplicably appeared to be devoured by something, people were terrified of them. In the Assyrian and the Babylonian cultures lunar eclipses were seen as evil omens; in ancient Greece solar eclipses were dreaded. Here is a fragment of a lost poem by the Greek Archilochus writing of the Total Solar Eclipse of 6 April 648 BCE. 

“Zeus, father of the Olympians, made night from mid-day, hiding the light of the shining Sun, and sore fear came upon men”.

About 2000 years later, things were still the same in Europe! John Milton captures the fears of the ages when he writes of a solar eclipse in his ParadiseLost (1650): 

Shorn of his beams, or from behind the Moon,
In dim eclipse, disastrous twilight sheds
On half the nations and with fear of change
Perplexes monarchs.

Predicting eclipses
Several hundreds of years of dread and observation made it possible for the Chaldeans, who, living in what is today’s Southern Iraq, perfected around 600 BCE the science of eclipse prediction. A famous story is told of Thales, the pre-Socratic Greek Philosopher from Asia Minor (Turkey), who based himself on the Chaldean calculation of saros and accurately predicted the Total Solar Eclipse of 28 May 585 BC. A saros is the calculation that similar eclipses of the sun recur in cycles of 18 years, 11 1/3 days (or 6585.3 days), because it takes that long for the sun, the earth, and the moon to return to nearly identical relative positions. Few took notice of Thales’ prediction then, but when the eclipse came, the two warring nations of Lydians and Medes were so startled that they stopped their 5-year war and signed an urgent peace treaty!

From calendars to understanding the Universe
Perhaps the first to have advanced beyond calendar-making to an understanding of the universe through watching an eclipse was the great Indian mathematician and astronomer Aryabhatta (476–550 CE) who watched a solar eclipse and proposed at the age of 23 his Heliocentric theory, a thousand years before the Polish Copernicus (1473 – 1543). Aryabhatta proposed that the moon caused the solar eclipse by blocking the sun, and that the moon only reflects light, just like the other planets.

The next time a solar eclipse led to a great discovery was again in India when, on 18 August 1868 in Guntur town near Vijayawada, through a spectroscopic study of the sun’s corona at the time of totality, European scientists discovered the presence of a new element: Helium. Helium is formed in the sun through nuclear fusion of hydrogen atoms, releasing the life sustaining energy that reaches the earth.

The total solar eclipse that is the most memorable in the history of science is that of 29 May 1919. Einstein’s 1915 General Theory of Relativity postulates that space could be distorted by gravity. If that were right, the sun’s massive gravity could bend even light rays towards itself. During totality, the scientist Eddington and his colleagues observed that light from the cluster of bright stars Hyades seen just behind the sun appeared to bend towards the sun. Einstein was proved right and Newton’s Theory of Gravity was replaced by the more correct Theory of General Relativity!

Not just for the scientists!
Eclipses come in all shapes and forms: there are solar and lunar eclipses, and they could be either partial or total.

A solar eclipse occurs when the moon comes between the earth and the sun, thus blocking the sun from the earth, sometimes partially, sometimes completely, sometimes only the centre leaving the edges of the sun exposed – called an annular eclipse, like that of January 15, 2010.

A lunar eclipse occurs when the earth blocks the sunlight from falling on the moon. As the moon does not emit light of its own and only reflects sunlight like a badly polished mirror (the moon reflects 7 percent of the light that falls on it, the earth reflects 39 percent), when sunlight is prevented from falling on the moon, it appears dark, like most other things in space.

Watching the awe inspiring Total Solar Eclipse

There are at least two lunar and two solar eclipses every year, somewhere on the earth. While it is true that an eclipse is just the play of light and shadow, a Total Solar Eclipse can be spectacular.

As the eclipse approaches totality, darkness descends rapidly and we see the fast moving shadow of the moon as shadow bands, because of atmospheric interference. Birds start returning to their nests to roost, and the animals are confused. It is an eerie feeling as twilight falls, the horizon line acquires a glow, shadows sharpen and darken, and one feels emboldened to look up and see the sun. And as the sun rapidly disappears, just moments before totality, sunlight peeking through one of the moon’s deepest craters creates the spectacular effect of the diamond ring.

On 24 October 1995 I was in Agra, where the Taj Mahal is located, to watch the Total Solar Eclipse. All of Agra town was huddled inside, fearing the evils an eclipse may bring. A few of us – a couple of hundred science enthusiasts – were perched on the ramparts of the historic Agra Fort to catch the eclipse. As totality approached, when the diamond ring revealed itself, there was a loud and collective gasp from all those who were there – and one of my new friends said “Now it doesn’t matter if I lose my eyesight. I have seen the most magnificent thing possible!” So overwhelming was the feeling of seeing our life giver, majestically perched in the sky in all his glory that it makes one almost irrational.

Catch it Before it is Too Late!
The sun is 400 times farther from the earth than the moon. And the moon’s size is almost 400 times smaller than the sun: so from the earth both the sun and the moon appear to be almost of the same size: this is what makes our solar eclipses possible.

However, as tidal acceleration is causing the Moon to move away from the earth by about 3.8 cms each year, and as the sun is steadily growing larger in size, in 600 million years the moon would have moved so far away from the earth (23 thousand kilometers) and the sun grown in size, that total solar eclipses will no longer be possible on the earth.

So watch them while you can!

Eclipses call for more special celebrations than New Years and Solstices. Write a poem, draw a painting, or have a meal to celebrate the celestial chiaroscuro non pareil!

(Readers may obtain a pdf version of 'Celebrating Eclipses', an illustrated booklet in English by Babu Gogineni, by sending a request to gogineniiheu [dot] org. The booklet looks at the cultural beliefs and the science around eclipses. –Ed.)

Babu Gogineni