Where do you live? A question, which has fascinated me since childhood and, which I assume, fascinates all children, if the mind-filling activities of schooling, TV, mobile phones and SMS, daily chores and pursuits leave any time for wonder about our place in the Universe.

To this quest, there are religious/spiritual answers as well as astronomical/physical ones. Today?s LIVE?N?LEARN is about the latter.

Before stars existed, the universe was almost entirely made of hydrogen and helium, the most basic elements. Once stars (or suns) formed, the intense heat at their centre fused hydrogen and helium into heavier elements such as carbon, oxygen, nitrogen, iron, etc. Then stellar dust gravitating around a star coalesced into planets, which remained in orbit around the ?mother? sun.

The Earth is one of ten planets orbiting around an ordinary yellow star. This star, our sun Sol or Helios, is one of the billions of stars known so far, and is situated in a fairly remote part of a minor arm of a typical mature galaxy or cluster of stars. How many of these stars or suns have planets, neither too hot nor to cold to support life, as we know it? Or different or very different life forms based for example on silicon and not carbon like our organic life?

If we were to find Earth-like planets beyond the Solar System with signs of organic life, then it could radically alter our perceptions about our place in the Universe, just as did Galileo?s assertion, 400 years ago, that the Earth revolved around the Sun. If, on the other hand, evidence starts to accumulate that life is very rare (or even that the Earth is unique?), then it will become additionally all the more important to protect the future of the diversity of living organisms on Earth.

Our size-scale. Begin with your classroom, school or house and move along an ever- increasing dimension, to your street, suburb, town or village, district, country, continent/ocean, planet Earth, Solar System, our Sun within the Galaxy (our galaxy is called the Milky Way), the Galaxy cluster we are part of (the Local group, with Andromeda etc) on to an apparently infinite universe, made up of billions of galaxies and trillions of suns or stars.

Consider these statistics:

• There are about 200 billion suns in the Milky Way Galaxy.

• The Milky Way Galaxy is 100,000 light years side to side.

• The diameter of the bulge in the center is 30,000 light years.

• This solar system orbits the centre every 250 million years, i.e. a galactic year.

• There are billions of such galaxies and trillions of suns like our sun in the universe.

Can you appreciate how small and insignificant we are, planet Earth? At the same time, paradoxically, how unique and important we, human beings, are in the unfurling of this universe?

Our time-scale:

• Big Bang: 12-13 billion years ago, creation?

• Our Galaxy (the Milky Way) formed: 5-6 billion years ago

• Sun formed: 5 billion years ago

• Planets formed: 4.6 billion years ago

• Life appeared on Earth: 3.5 billion years ago

• Carboniferous period (coal, oil, natural gas formed): 200 million years ago

• Man on Earth: 1 million years ago

• Civilisation: 20,000-8,000 years ago

• Birth of main religions: 4,000-1,400 years ago (birth of Christ 2,000 years ago)

• Man leaves Earth for (albeit limited) travel into space: 45 years ago

• Man invents technological brain (computers), man discovers the genetic code

Today, as we complete any thought or action it immediately becomes part of the past, of history.

Images of space and time. We see light from distant objects. Light travels at 300,000 km/s. Fast, but not infinitely fast; it takes time for light to get to us, for example

It takes 8 minutes for light to get from the Sun to us; so we see the Sun as it was 8 minutes ago.

It takes 4,3 years for light to get from the nearest star to us; so we see that star as it was 4,3 years ago.

The Andromeda galaxy, part of our local Group of galaxies is 2,5 million light years away, so what we see with a telescope (or with the naked eye, since Andromeda can be seen thus) is that galaxy as it was 2,5 million years ago, when that light left it!!

We define a light-year as the distance travelled by light in 1 year: 9,460,000,000,000 km, nearly 10 trillion km. The science of Astronomy is thus a sort of time machine: when you look out in space you are looking back in time. At present the outer confines of the known universe are situated at about 100 million light-years away! Calculate how many kilometres that is and, on the human time-scale, how many generations of people!

Leaving the daily-life thoughts and activities for what should be properly called a meditation on our place in the universe can only expand the mind, while at the same time infuse a healthy dose of humility into our thoughts.

<B>Dr. Michael ATCHIA

[email protected]</B>