The power of periodicity:
There is a day every month that the Indians offer their prayers to their ancestors or the departed which is on the New moon. The ancient tradition also included a special day, mahalaya amavasya, to remember all of them in case someone missed their monthly offering. I really like the way our ancestors used astronomical events to remember the dear departed.
While we are on this subject, one incident from the final battle of the great epic Mahabharata comes to mind. The author Veda Vyasa uses an astronomical event to indicate the time of the battle of Kurukshetra. This event happens on the 14th day of the battle where Krishna uses a Solar eclipse during the sunset to help Arjuna. Arjuna uses this distraction to avenge his son Abhimanyu’s death, by slaying Jayadhratha.
Though there is no strong evidence to prove this, as an astronomer I can use the knowledge of positional astronomy and periodicity of eclipses to attempt an estimation of the date of occurrence of the eclipse at Kurukshetra and hence the battle itself. For all this, we must assume that the battle really happened. Historians have tried this estimation and have arrived at a variety of dates for the battle, ranging from 5561 BCE to 950 BCE.
Whatever the timeline and the context, I am just mind blown by how the simple process of periodicity has kept us all at the edge of our seats when it comes to the beauty of the Universe.
Human life span
There is another such periodicity that left me speechless when I first encountered it in a completely different context. The maximum lifespan of a human is believed to be around 121 years, give or take a few years. These 121 years can be divided into 11 cycles of 11 years each. The first 11 years is childhood, then youth for the next 11 years and so on. Now let us look at what Galileo and his contemporaries did with the observation of the Sun. They discovered a black patch on the solar surface and called it the Sunspot. They observed the spots for a very long time since then and don’t be surprised, we watch them even today and record solar spot activity to monitor geo-solar weather patterns. That aside, the relentless observation of sunspots over centuries has revealed that the sunspot cycle is also of an 11-year duration in which the spot activity increases and decreases every 11 years. The current cycle and the spot counts for the day are available on the internet. There are satellites that are dedicated to this activity.
Knowing that the sunspot has an 11-year cycle, I was curious to know how old the Sun was. A rough estimate gives us 4.5 to 5 billion years as the age of the Sun. Now, do you know what a cosmic year is? Let us learn what this is.
The next interesting periodicity is the revolution of the Sun around the galaxy. This takes around 225 to 250 million years; this is called the cosmic year. So, estimating the sun’s life at 5 billion years as of today we have gone around the galactic centre 20.5 times. That means the Sun is just 20.5 cosmic years old. But the galaxy is much older than the Sun, which leads to the question, how old is our galaxy, the Milky Way?
The current estimate of the age of our galaxy is roughly 13.4 to 13.6 billion years (BY). This is very close to the current estimate of the age of the Universe at 13.8 BY. This means that our galaxy has been around for a very long time and has seen the evolution of the Universe.
Now, a series of very interesting questions popped in my head. If Sun is only 5 BY old and the galaxy is 13.6 BY old, then what was the Universe like before the birth of the Sun? How was the Sun born? How do we understand the beginning of life? The journey of finding the answer to these questions has many interesting twists and turns, both literal and metaphorical.
The human quest for knowledge started with the observation of nature and experimenting with surrounding materials. This has led us to understand a variety of things about nature. We have stumbled across magnificent ideas and truths about nature. For instance, the idea of evolution, the concept of vaccination, the science of medicine to cure the human body and many more. The most fascinating of all discoveries, according to me, is the periodic table of elements.
Chemistry to Astronomy
Stay with me, I am going to connect this Chemistry class to Astronomy very soon. The study of various substances led to the discovery of the elements of the periodic table. The study of a few elements under fire or an arc of light led to the discovery of elements on the surface of stars. Yes, the spectral study of elements and compounds that originated in Chemistry labs revolutionised the understanding of the universe!
The atomic spectra recorded in labs were available for comparative studies with the spectra of starlight. This dates back to the rainbow in the lab of Sir Issac Newton. It was not until the 1800s that scientists realised that the chemical composition of stars and galaxies are the same. This study of the chemical composition of stars revealed to us that the chemicals are seen on the surface of Earth and the chemicals in our body must have come from stars.
Further, spectral analysis of the composition of the planetary atmosphere in the solar system revealed that chemically, the overall composition is the same. Then the study of the neighbourhood stars and galaxies revealed that Universe kept it very simple at its inception. I mean the chemical composition of the majority of the Universe is ‘Hydrogen’ – the simplest of all atoms. Then the question is, where did the other elements come from? The answer to this question lies in the process of stellar evolution – from Hydrogen to Iron to Uranium through various nuclear processes.
At this point I want you to pause for a bit. Do you realise that everything in our system, the vitamins, minerals, genes, DNA, all of us in this world, are created from the material that was once synthesised in the centre of a star that gave its life to create a new one?
I feel it is our responsibility to understand this underlying truth of the oneness of humanity and all forms of life. The Universe is effectively screaming to us through the light of the Sun and the stars. The sense of one world, one family can be brought about by educating the entire population about one single subject – Astronomy. It has taught me the essence of life and the purpose of our existence.
Let me leave you with this question. Is there life anywhere else in the Universe? I feel that there is, and we will find it eventually. Otherwise, it is an awful waste of space, if we are the only freaks of nature. Now if we are alone, then it is our responsibility to explore the Universe and keep our eyes open for the next surprise it has for us.
As we continue our battle against the COVID19 crisis, let us remember that there are things that can cross human-made boundaries and wreak havoc in our lives. It is sensible for us to remember that we are all same chemically and what happens to one can happen to anyone in the world.
Stay home and stay safe!
Sriraghavan S M
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