Friday, 8 April 2011

Speed of Light: Properties

This post is going to be the first of two; in this I will discuss light and it's basic properties. And my next post will talk about what the limitations of light being finite is and what the implications of this are.

The speed of light is often something that is mentioned in physics, and many people are aware of the basic principles of the speed but not of the implications.

You may or may not be aware that light travels at 299,792,458 metres per second in a vacuum, which is about 670,616,629 miles per hour. That is incredibly fast. That is as fast as any information can travel, the fastest possible thing is light.

This immense speed may seem instantaneous, and when on Earth it virtually is. As in one second something travelling at the speed of light would circle the Earth 7.48 times, which is so fast it is hardly worth considering it is not actually instant.

But when we begin thinking of distances between planets, solar systems and galaxies we have to think in terms of light. In fact, the light we see from the Sun is actually from the past. It takes 8 minutes for light to travel from the Sun to Earth so every light beam we see is actually from 8 minutes in the past and if the Sun were to miraculously disappear in an instant we would have no idea for 8 minutes.

The second closest star to us (after the Sun of course) is, Alpha Centauri, which is a system of 3 stars: Alpha Centauri A, Alpha Centauri B and Proxima. The closest of the three is Proxima, which is not visible to the naked eye because of the brighter Alpha Centauri's, but is actually slightly closer to Earth at 4.24 light years away compared to Alpha Centauri's 4.37 light years.

A light year is the distance light travels in one, obviously. Which is about 5,878,625,373,183 miles. The second closest star to us is about 24,925,371,600,000 miles away; the closest star to us after the Sun. That's why it is preferred to use light years (or parsecs) as a unit of measurement in astronogy.

The galaxy that we are inhabitants of (the Milky Way) is about 100,000 light years in diameter and 1,000 light years in thickness. Which is huge (about 587,862,537,318,300,000 miles in diameter), this is only one of a potential 500,000,000,000 galaxies in the observable universe.

And the stars at the edge of our galaxy are viewed as images that are around 100,000 years old. We do not know how they've changed since then and it will be another 100,000 years before we see how it is today. There is something magical about seeing something that is in the past, and it is this property, the limitation that light is not instantaneous that allows us to trace back the roots of the universe.