Having laboured through the alphabets from A to K/L, and discovered a small portion of the world of astronomy in the process, we are tempted to move on. But not before we delve on to a unique portion of astronomy/universe which seems to have escaped our fancy thus far. Not wholly, though.

Local group of galaxies: Galaxies, as you well know, are like continents of stars gravitationally, but loosely attached to each other. They do not loiter independently, but most are grouped into clusters often containing dozens, even hundreds of galaxies (occasionally thousands of them), living and breathing in unison, bound by mutual gravity.

Just imagine, for instance, one or even two thousand galaxies locked together in a gravitational embrace of sorts. For me, as a full time, life-long astronomer, it is impossible to perceive how so many galaxies consisting of tens of thousands of billion stars can float together with trillions of miles of void between them, while the resident stars, and galaxies themselves, swim across the open void crisscross. It just beats me.

For that matter the whole universe with all its galaxies, and what not, could be a massive — unimaginably massive — cauldron of galaxies, all racing away from each other, black holes and all, yet in one eventual direction. It’s a bouncer that eludes me!

Our own galaxy, consisting of some 200 billion stars, is part of a comparatively small cluster known as the Local Group. the two best known galaxies in this group are the Milky Way and the lovely Andromeda. Andromeda, being just one of them, is far larger, consisting of as many as 1,000 billion stars!

The two lesser members of this neighbourhood are the Small Magellanic and the Big Magellanic Clouds — dwarf galaxies containing about 20 billion stars each. These ‘little’ galaxies, long regarded as nebulae, are only visible properly from the southern skies.

In the Local Group there are some 25 galaxies. They all do not move in the same direction, but generally they do. Like a swarm of bees that never loiter far from their hive, the nature of galaxies is an interesting phenomenon no doubt, but the behaviour and attitude of the group is far more captivating.

Andromeda and our Milky Way galaxy are rushing towards each other, poised for an eventual head-on collision, which should come about in a few million years. But that will not be as disastrous or apocalyptic as it might appear to us. Instead, Andromeda, despite being much larger as you know, will race through the middle of the Milky Way without causing much damage, and escape from it virtually unscathed. It is another matter that the black hole in the middle of our galaxy, powerful as it is, will disturb Andromeda to the extent that some portion will be devoured by the Milky Way, and Andromeda will be shorter by a few stars. You and I will stay unharmed, if we are around in a few million years!

Lookback time: Interesting again! The more distant an object is being observed, the older is the information received from it. It is the history of the universe in light form. Say, when we look at the moon, the picture it presents is pretty recent — just 1.5 seconds old approximately (238,000 miles divided by 186,000 miles). Things begin to get less clear-cut when it comes to the Sun: it takes its light a good 8 1/2 minutes to reach us.

Then there are objects in space that could be one light year away; that is, their light travels for one year, or six trillion miles (one followed by 12 zeros) before it reaches our eyes. This, as you know, is called one light year or 1ly. So, a star or galaxy may or may not be there, but we see it as it was then, when its light left its shores for our eyes.

There are stars which are five or 10 or 50 light years away — or even further. Their light takes that long to reach us. It also means that we are looking at that part of the universe which was as it was five or 10 or 50 years ago, which also means that we are watching the history of the universe unfold before our very eyes, as I said earlier.

Again, imagine if a star is 160ly away. We are looking at it as it was at the time The Great War of Independence was being fought in the sub-continent. Again, its light left the star on its long journey 160 years ago. That particular star may or may not be there at this time, but a true picture will be revealed to us only that many light years later when its light covers all that distance and reaches our cornea and reveals the true story.

Published in Dawn, Young World March 25th, 2017