Dear All,
In a second light travels about 300 megametres.
In an hour light travels about 1 terametre.
In a year light travels about 10 petametres.
At some time in the future, astronomers � who appear to be slow learners �
will describe the distance that light travels in a year as 'about ten
petametres' or � using symbols � as 'about 10 Pm'.
This is roughly equivalent to the old unit, still used by some (many)
astronomers, called a 'light year'. The old 'light year' was approximately
equal to the speed of light multiplied by the number of seconds in a year
(299 792 458 metres per second multiplied by 365.25 days multiplied by 24
hours multiplied by 60 minutes multiplied by 60 seconds is approximately
equal to 9.46 x 10^15 metres). Please note that I have used 'approximately'
deliberately, because I have never heard any astronomers specify the type of
year that they are using for their estimations. Is it a solar year? Is it a
sidereal year? And so on.
Clearly astronomers have never felt a need to be very accurate or precise
about 'light years', and so for me, 10 petametres is roughly the right
distance and it is much simpler and easier to use and to think about.
Cheers,
Pat Naughtin
CAMS - Certified Advanced Metrication Specialist
- United States Metric Association
ASM - Accredited Speaking Member
- National Speakers Association of Australia
Member, International Federation for Professional Speakers
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