Measuring The Speed of Light

More than a measure of distance the speed of light is a measure of time – once that makes sense, a light will shine on the cosmos. Most of us have experienced mind drifting time outs, that perceptible moment of realization when eyes glaze as confusion sets in – light speed exasperation needn’t be one of them.

Light travels at 300,000 kilometers per second – multiply the number of seconds in a year by distance light travels per second and you have a light year – approximately 9.5 trillion kilometers. Such daunting distances lend themselves to glassy eyes, so astronomer Robert Burnham Jr. devised the measure of AU (Astronomical Unit – 1 AU being 150 million kilometers, or the distance from Earth to the Sun ). One AU is about 8 minutes – the time it takes sunlight to reach Earth. One light year is equivalent to 63,000 AU. By mind blowing coincidence, there are 63,000 inches in a mile.

Scaling the astronomical unit at one inch, here are distances to various stars, star clusters and galaxies:

Alpha Centauri: 4 miles

Sirius: 9 miles

Vega: 25 miles

Fomalhaut: 25 miles

Arcturus: 37 miles

Antares: 600 miles

Pleiades open star cluster: 440 miles

Hercules globular star cluster (M13): 24,000 miles

Center of Milky Way galaxy: 27,000 miles

Great Andromeda galaxy (M31): 2,300,000 miles

Whirlpool galaxy (M51): 37,000,000 miles

Sombrero galaxy (M104): 65,000,000 miles

Distance established, what about time? Brian Cox of BBC’s Wonders Of The Universe said – “the speed of light is the speed limit of the universe, built into the very fabric of space and time”, “the further away an object is, the further back in time we see it”. Starting to glaze over? Relax, take a deep breath, spend 3 minutes watching this video. I promise you’ll feel better –

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5 thoughts on “Measuring The Speed of Light

  1. You shouldn’t have mentioned the ‘inches in a mile’ thing. The conspiracy theorists and godbotherers will be all over that one.
    Worth bearing in mind that the AU isn’t a constant, since the Earth’s orbit round the Sun is an ellipse. It’s an approximate mean value.
    Just saying. 🙂

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