SO wrote the great storyteller of yore, describing Achilles’ helmet. On the contrary the comets are, or were, no more malicious than those who stabbed Julius Caesar (100 BC-44 BC) to an agonising death, or those thousands who spread death and destruction on millions throughout the recorded, or unchronicled, spans of history.

While comets do not, or cannot, spread death and destruction or pestilence, they do seem like fearsome visitors from deep space who appear whimsical yet are among the most photogenic of all space objects, despite being as harmless as any other space personality.

Although the so-called tail of the comet may be a million miles long or even longer, the comet itself is indeed no bigger than a few miles across from end to end. Surprising? The most famous of them all, Halley’s Comet, is also among the biggest of them all. An occasional comet may turn out to be a real big thing (a few tens of kilometres across) but we are not sure. An average comet is much like a boulder or a round piece of real estate up for grabs, with the difference that the face is heavily pock-marked.

Cratered all around, punched on its face by the rushing rocks and boulders scrapping from its surface all those tiny shards that appear in our skies later on as shooting stars or meteors as they dump millions of tonnes of space garbage on the surface of planet Earth. On other planets and moons too, the cometary debris is not dumped suddenly but in incremental tiny bits and pieces.

The chipped material comes rubbing against the earth’s atmosphere either from comets or from the surface of asteroids and at night these appear as lovely bright streaks of light as they dart from the top of the sky towards Mother Earth. Those of us who get to spend a night out watching them can never forget the regal sight. More about shooting stars, meteors and meteorites later on.

Understanding comets

In order to understand comets and even fall in love with them, we must understand a few things about them: their origin, their orbits, their nucleus, the tail, the coma, and of course the debris they leave behind. Let us take them up one by one, starting with their origin.

It is famously assumed that there are billions upon billions of comets around each stable star. They reside pretty far away from the star. The swarm may be in a halo some hundred A.Us away from the star. This is popularly called “Oort Cloud” in honour of the famous Dutch astronomer and mathematician named, Jan Hendrik Oort (1900-1992), who presented the theory in 1950. Another potent source of comets is a region called Kuiper’s Belt, a region in space some 35-50 A.Us away.

So, this Oort cloud is the original home of comets. It is another matter that in the course of their shenanigans, one or two of them get nudged inward towards the centre of the Solar System. These are then trapped by the gravity of one planet or the other which propels them towards the Sun. That is how comets circle in elongated elliptical orbits, sometimes even parabolas.

You already know about nucleus, which is at the centre and forms the crux of the matter.

Coma

Coma develops gradually as the heat of Sun gradually leads to a puffed up body of gasses and dust that lies embedded deep inside the craters of the nucleus. As it crawls closer, a tail of volatile matter develops and appears as “cylinder” I spoke earlier. Once having swished past the Sun at the highest individual speed, the comet again contracts in both size and tail — until it disappears completely only to reappear some years later.

The shooting stars we see at night are the remains of comets; their loose material abandoned by them after their rendezvous with the mighty Sun.

The celestial objects that kept hapless people of old time in bewildered for so long (some even paid with their lives for their inability to predict them) were actually not to blame for any misfortune of a wide variety. In fact, men have always suffered, and always will.

For what remains despite the lapse of many billion years is the fact that bacteria, viruses, amoeba and pests have survived and are thriving despite our awareness and means to destroy them. Little tangible effort is made to do just that. Hence the endemic waves of malaria, plague, Aids and now Ebola. Numerous other endemic diseases appeared and laid waste whole armies, and human settlements which had no answer to these ‘wraths from gods’.

In two and a half centuries, that is between 1300AD-1550AD, some 25 million people perished in Europe alone. Often there was no one to bury the dead. Besides, millions died in famines. All the way from China to the Americas through Asia; we are forever at the mercy of hunger and pestilence. Yet in some countries of the world, millions of tonnes of standing crops of cereals and what not is actually torched every year to keep the prices stable.

Any comets caused them? It is up to you, young people, to find the answer, better than our hapless forefathers did.