Re: Perseus arm is closer than thought
- From: "tadchem" <thomas.davidson@xxxxxxx>
- Date: 9 Dec 2005 08:38:48 -0800
Sam Wormley wrote:
> Perseus arm is closer than thought (Dec 8)
> http://physicsweb.org/article/news/9/12/8
>
> Astronomers have made the most accurate measurement ever of the distance
> from the Sun to the Milky Way's nearest spiral arm, known as Perseus.
> They estimate the distance to be about 5.86 x 10^16 kilometres (around
> 6,198 light years), which is more accurate by an order of magnitude less
> than previous calculations. The result resolves a long-standing
> discrepancy between two different techniques for measuring distances in
> the Milky Way and could also help us improve our understanding of how
> such spiral arms form (Sciencexpress 1120914).
http://www.sciencemag.org/cgi/content/abstract/1120914v1
The estimated distance is 1.95 ± 0.04 kiloparsecs. The uncertainty is
about 2% (=0.04/1.95).
The value "6,198 light years" represents a gross misuse of a calculator
and a lack of understanding of 'significant figures.' Given the
uncertainty in the original number (*always* just as important to a
measurement as the raw magnitude itself), those last two digits are
*not* significant.
A better value (in light years) would be "6,200 ± 120 light years."
Tom Davidson
Richmond, VA
.
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- Perseus arm is closer than thought
- From: Sam Wormley
- Perseus arm is closer than thought
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