Cosmic Knowledge: Distances

10 miles (16 km) to work, 900 miles (1,450 km) from Denver to Austin and a whopping 10,000 miles (16,000 km) from NYC to Sydney, Australia!  Even as the commute to work may be manageable, a trip to Australia can seem gigantic.  So, what about distances in the Universe?  Just getting to the Moon is around 385,000 km, which would be 12 trips to Australia and back.

A trip to the Moon however is nothing in context of the Universe.  The Sun, at 150,000,000 km, is considerably further away.  Neptune is 4.5 billion km away from the Earth and the Orion Nebula is 10,000,000,000,000 km away.  That equals 1,200 light years, which is the more pleasent unit, if you consider the fewer number of zeros.

Such distances are difficult to grasp and meters or kilometers (or miles, feet or inches) a units of measurement, that are almost useless when it comes to describing the gigantic distances between planets or stars.

As a result, astronomers utilize other measurements.  The most well-known unit is the Light Year (LY), used to describe the distance between galaxies or stars.  The parsec (PS), made famous, correctly or incorrectly (debatable), by one of the greatest film franchises in the world, is also used for this purpose.  Another unit of cosmic measurement used for distances in the solar system is the Astronomical Unit (AU), which is the distance between the Earth and the Sun and consequently equals 150,000,000 km.

An overview of the measurements, which astronomers use, can be found in the following table:


Astronomical Unit (AU) 149,597,870 km or 8.32 Light minutes
Lightspeed 299,792.458 km/s
Light second (Ls) 299,792.458 km
Light minute (Lm) 17.99 Million km
Light hour (Lh) 1.08 Billion km
Light year (Ly) 9,460.5 Billion km
Parsec (Ps) 3.262 LY or 31,000 Billion km

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