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 –

Pondering Light Years

Technology capable of imaging cosmic formations at unattainable distances from Earth, led to pondering light years. Most everyone knows the terminology, understanding at some level the vast, unimaginable scope of our universe. I find myself wondering how many actually comprehend the magnitude of a light year. In the spirit of imagination and wonder – my armchair grasp of light years….

Light reigns as “fastest” in the known universe – 186,000 miles per second to be precise. To put this in perspective, in a single second traveling at the speed of light you would circle the equator 7.5 times. Multiplying the number of seconds in a year by the speed per second, you would have to cover 5.88 trillion miles in a year. Putting close to 6 trillion miles a year in perspective is mind numbing. Try picturing a light minute – it takes about 8 minutes for sunlight to travel 93 million miles to Earth. Visualize 525,600 minutes in a year, ponder 8 of those minutes evaporating in 93 million miles to the Sun.

American astronomer Robert Burnham Jr. published Burnham’s Celestial Handbook in various forms between 1966-1978. Burnham popularized the astronomical unit or AU. One AU = 93 million miles and/or 8 minutes of light speed. Coincidentally the number of AU in a light year and inches in a mile happen to be 63,000. All you have to do now is draw a mile long line in the sand to represent a light year – one inch of that line is the distance to our sun.

Extend that mile long line to slightly over 4 miles, you’ve arrived at Alpha Centauri, the closest star system to our own, 276,000 times the distance from Earth to the Sun. If modern technology attempted the 4 light year road trip to Alpha Centauri – it would take well over 100,000 Earth years.

Ponder 26,000 light years to reach the centre of our Milky Way galaxy, estimated to be over 150,000 light years wide. The Andromeda galaxy is 2 million light years away.

Contemplating light years is heady stuff. The next time you gaze at night’s sky, take a moment to wonder. Ask yourself how¬† long it took for starlight to cross the cosmos.