When you look at the clear night sky, you see stars-those tiny diamonds suspended in the vast pitch-black emptiness. But stars shine because…? Our own sun, which is a star, emits light. Stars are like giant bulbs but are much more powerful.
Light travels at a speed of 3.0*108m/s in vacuum and space is mostly vacuum. In other words light can cover a mighty distance of 300 000 000m in only 1 second!
The thing is that 300 000 000m is a just one of those small amounts in space. Other stars are billions of kilometres-let alone metres-away. Astronomers in fact use light year as the unit for distance. One light year is the distance travelled by light (in vacuum) during one year. Therefore one light year equals (300 000 000*3600*24*365)m.
A single light year is definitely huge: 9.46 trillion kilometres-no need to put this in digit form-in fact. But where exactly do I want to converge? A star that you see in the night sky is not one but many light years away. This means that it is very far away. But most importantly, it means that light from this particular star takes many years-and not mere seconds-to reach your eyes! So what?
When you watch a star, you are actually only seeing the light it emitted years ago. At present, the star may be somewhere else in the night sky. (Stars do move in space). It might have deflected a little to the east or north or north-northeast. The star is still emitting light though. This light will however be seen in the following decades or even centuries; or simply next year.
When you watch stars at night, you are actually looking in the past. So who or what is time travelling? The star? You? Or light? The further something is from you, the further in the past you are penetrating into.
Maybe then, someday, the newest technologies will be able to observe these seconds after the Big Bang-if it ever occurred in the first place.
About the Author
Khalil A.Cassimally is the editor in chief of Astronomy Journal and Astronomy Journal Ezine. He is also the co-founder of the RCPL Astronomy Club. He is currently Senior Columnist at BackWash.com and Columnist for bbc.co.uk h2g2 The Post where he writes 'Not Scientific Science' column.