“A light year” – is the distance in length travelled by light relative to a single Julian year (365.25 days) of earth. Total distance a light travels in a Julian year is around 5.878 trillion miles. Which makes the speed of light at exact 186,282.4 miles per second in a vaccum. Yes that’s “per second” – the single most unified unit of time.
Just to give you an assumption of how fast the light is; consider a beam of light is shot at one end of earth, it will reach to the same point, travelling around the circumference of earth which is 24,859.82 miles, in 0.133 seconds. That means, the same beam of light will complete its 7 orbits around earth in just one second.
This speed of light is universally constant. And in the whole wide universe – 92 Billion light years across – nothing, yet, travels faster than the speed of light – quantum physicists though won’t agree to it. It was the great mind of Albert Einstein who defined to us how light works. What it is made of. And how relative it is with time, through his theory of General Relativity and photoelectric effect.
Our universe is 13.7 Billion years old. That’s the time of BigBang. And our solar system, dominated by The Sun, is about 5.4 Billion years old. And our blue planet, our earth, is around 5 Billion years old.
This difference of age between the existence of universe and our solar system proves that before us, for 8 billion years, this universe still existed. And thrived. And expanded exponentially. And through the destruction and construction of stars and their stardust, our solar system evolved. And ultimately after millions of years of evolution, through single cell organisms, humans came into being. We are made of stardust.
Our universe is comprised of galaxies, blackholes, stars, nebulas, planets, dark energy and dark matter. There are around 400 Billion galaxies in our Universe. And in the galaxy where our solar system is growing old has more than 400 Million Stars. Each one like our Sun. Many similar, many more massive, and many more powerful.
Our closest star system is Centauri. There are not one but three stars in that system. Their planets however are undiscovered. Among them the closest star is Alpha centauri. And it is about 4.5 light years away. Which means if we plan to travel there for any space adventure at the speed of light, aforementioned, we shall reach in 4 years and 5 months. Its just another star in our galaxy of 400 Million stars.
Our closest galaxy, The Andromeda, is about 4.5 Million light years away. It has its own stars, its own blackholes and its own planets. Andromeda and Milkyway are just two galaxies out of 400 Billion in Universe.
I would have to write a full book to explain everything I have talked about here. It would perhaps take me a lifetime considering my schedule nowadays.
Remember to look up, to the stars and see where have you come from. There are others out there. Somewhere, in some blue planet orbiting around a yellow dying star. You have neighbors. Still to be found.