Distant beauties of the past

6 05 2013


Many times we hear artistes in love songs compare their better halves to the stars in the sky, pretty much as love poets go on and on about how much the beauty and charm of their significant others closely resembles, or even surpasses, that of the ever shining night lights of the sky.

For the past year or so, I have been working in an environment that guarantees me full view of the sky at any time of night, albeit not in the picnic kind of setting. I have therefore been able to observe and appreciate the awesomeness and perfect order of things in creation, specifically those things in space; the sterling splendour and infinite sparkle of the gazillion masses of gas in space.

But it hit me that we actually embrace the magnificence of their past. That is, they are not as we see them when we look at them today. Perhaps they aren’t even there today. Puzzling? Thought so too.

Most stars are positioned at impossible distances from planet earth, where we reside. I say impossible because it is not possible for any human to travel there using the current technology, even in ten lifetimes! The fastest spacecraft ever launched from earth is NASA’s NEW HORIZONS (NH), currently cruising towards Pluto at a speed of 70,000 km/hr.

The nearest star to the earth, the sun is about 150 million kilometres away. Light from the sun takes approximately nine minutes to reach the earth’s surface. So instead of saying “the sun is so bright”, consider saying “the sun was so bright nine minutes ago” to be more appropriate. NH could do that journey in 90 days. But let’s not talk about that, we wouldn’t dare the temperatures.

Other stars are located so far away that writing their distance in kilometres would be cumbersome, so scientists devised a more convenient unit of measure for these huge distances – the light year. Now that sounds like a unit of time, doesn’t it? A light year is the distance light travels in a vacuum in one Julian year. A Julian year is made up of 365 and one quarter days, each lasting 86,400 seconds. That’s the calendar year we’re accustomed to. Taking the speed of light to be 299,792,458 m/s, this translates to exactly 9,460,730,472,580,800 metres. Without looking, what were the last four digits?

Another unit of distance in astronomy is the parsec. A parsec is the distance from the sun to an astronomical object which has a parallax angle of one arcsecond (1/3,600 of a degree). The name “parsec” is an abbreviated form of a distance corresponding to a PARallax of one arcSECond. One parsec is about 30.9 trillion kilometres. Imagine that.

Let’s look at a few other stars. After the sun, the nearest star to earth is the Proxima Centauri. This star is 4.2 light years away from planet earth. That means light from that star takes 4 years and 73 days before we can see it, which means that the light emitted by that star today will reach us 4 years and 73 days from now. Interesting, isn’t it? To travel there in the NH, it would take 18 calendar years. Next is the Alpha Centauri at 4.3 light years.

But a vast majority of stars are tens of light years away. The Sigma is at 11.6 light years away. That means that when you look up into the sky tonight and see the Sigma, you’ll actually be seeing it as it was 11.6 years ago, not as it is today! You’ll have to wait 11.6 years to see how it looks today. Using the NH, you would get there in around 50 years.

The Polaris, better known as the North Star, is about 323 light years away, according to a most recent study. By now you already know what that means; that we are currently seeing it in its past form – as it was 323 years ago. The stars of the famous Orion constellation, which are some of the brightest in space, are between 243 to 1,360 light years away. Let’s not even calculate how long it would take you to get there.

Several other stars are tens of thousands of light years away; it will take quite a while for them to be seen by earthlings as they are today.

So now you see what I meant when I said that when we look up at the sky and marvel at the perfect gorgeousness of the stars, we are actually getting impressed by their past. Probably some of the stars we see today burnt out years ago and are no longer in existence, but their absence will only be noticed thousands of years from today.




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