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Astronomy: Our shepherd star

September 22, 2012

No final truth about the universe has lasted. This was true for physicists at the end of the 19th century who believed in the Newtonian vision of nature. It will also be true for cosmologists today who believe they are on the verge of a theory of everything.

The sun has been the earliest and the most profound inspiration and source of enchantment for man. He has basked in its bounteous sunshine, revered it, learned to grow crops in rhythm with its intensity, held festivals to honour it, sung in its praise, wilfully offered bloody human sacrifices, and, deified it as a god.

Made immortal by imaginative and creative friezes and other forms of art in the pyramids (both Egyptian and Aztec) and elsewhere in the ancient world cultures, the sun was (and still is in many cultures) regarded as the giver of life. Its astronomical symbol alone amply suggests it.

In the Egypt of antiquity, the sun-god Ra arose from the east, rode across the sky majestically in a large boat chaperoned by several bare-chested Nubian slaves, until time for it to take a much deserved rest in the west. Keeping a kind profile, it smiled softly on the forthcoming crops and barley along the banks of Nile, helping them ripen.

Among the Greeks, the sun came to be regarded as the most benign source on earth that sustained all other sources. Sol (sun), solis (solar), pertaining to sun, were the most salient and prominent lexical terms (dictionary expressions). To some others, polis, citas, civic, democratis were. But we will leave it at that!

To our own ancestors, Surya Bahadur embodies life and largesse; kings and commons alike, submitting, submitting to its authority and bowing before it in submission and reverence.

Not just by far, in fact the sun is the most, the only important object in the skies. It is the giver of life: of all flora (vegetation), all fauna (animals, from bacteria to the largest whales) and is also the harbinger of the conditions that create and sustain life.

Water, air, gasses and even the rocks and boulders, minerals and soils and other forms of wealth that bring about prosperity and happiness to mankind. Hence, hope for some, despondency for others!

All of these, and more, owe their existence to the sun. I will go to the extent of saying that even ‘nothing’ owes its existence to the mighty, effervescent, smiling, fatherly sun!

Yet, sun is an average size star. Not very big, not small. Most of the stars in our galaxy, the Milky Way, are smaller, though the comparison almost ends there for most of these have attributes special and exclusive to themselves.

It is not too hot, not too cold for us at that distance (150 million km) to deny the benefits of its largesse. It is very stable in output. In any case, by being at a safe distance, and blessed with a covering (umbrella) of benign gasses, the earth is safe from the sun’s intense heat, besides bombardment of its lethal, incessant ultra-violet rays and other forms of radiation. Although the sun has been a source of myth, mystery and wonderment, and hope to the woebegone for thousands of years, until only a few generations back no one really knew or understood how the sun produced its heat, or how it managed to send endless streams of light, heat and radiation of a wide variety for billions of miles into space. Planet earth (or any other planet, moon, asteroid, or comet) may turn its face away in the course of its axial rotation, the sun is there to light it up just the same.

No rest or respite for the poor old sun!

By and by the secrets of solar (sun’s) activity began to unfold — until man finally understood the intricate processes that cause and govern the furious activity on its surface, and deep down in its centre. Man even began to duplicate the very processes of nuclear fusion that prevail inside the stars, here on earth.

Stellar activity (actions on the surface, and the centre of the stars, in this case the sun) is intense, incessant and unstoppable, taking place at nuclear level under conditions of great, unearthly commotion caused by heat (millions upon millions of degrees ), and unimaginable pressure (let’s call it gravity ).

The two create a third force that of nuclear fusion that is the source of the demonic power a star possesses. Pressure of trillions upon trillions of tons of matter (gravity) and the outward force created by the maddening nuclear explosions sort of cancel each other so that the star remains stable.

What stability! Would my friends like to have stability like that?

Proto stars had to toil hard, very hard to attain the required equilibrium, and the status quo. Therefore, sun and other stars don’t burst apart, or collapse on themselves.

Let us try to imagine an earthly situation of how heat is created even if the example is very ordinary and of mundane nature.

All of us have some experience of winter. Think about the time when cold weather compelled you to wring your hands and rub your palms furiously to make them warm. That helped create heat and transfer some of it to the portions of body near the palms.Small examples help us understand big things better. But nobody should ever imagine that heat in the centre, or surface of a star, is anything resembling the gentle heat generated by palms of human hands. For heat and other forms of radiation to travel billions of miles into and across empty space is another matter. For that to happen, some other force must be at work.

But how does that come about?

As stated earlier (but not in the same words) there is a trinity of forces at work in the universe. They interact on each other and do so fiercely and ferociously. These are matter, gravity and nuclear fusion which interact upon each other and make a star what it is: a furious, tumultuous inferno. Just remember this for this will keep coming back into our reckoning.

Before we deal with stars any further, let us consider what term is used to measure and describe heat, for we shall need this too from time to time.

Kelvin — in astronomy as in most other sciences, temperatures are expressed in Kelvin scale. These are measured from absolute zero, that being the state of matter that contains absolutely no extractable or noticeable heat, i.e. molecular motion comes to a complete stop. Dead stop. Hence no heat is emitted. In reality no object can be as cold as absolute zero for even molecules of gadgets employed to measure temperature will come to a complete stop!

In Kelvin scale absolute zero is 0K, freezing point of water is 273K, and boiling point of water is 373K. The scale is named after the Scottish mathematical physicist William Thompson, Lord Kelvin (1824-1907). We shall need Kelvin scale every now and then.

More about the sun in the next issue!

“He burned his house down for the fire insurance and spent the proceeds on a telescope.” — Robert Frost

The writer is a professional astronomer and a former head of PIA Planetaria. He can be reached at