[LEAPSECS] 1.26 microseconds

[Rob Seaman]

Hi Zefram,

Thanks for saving me the trouble of commenting in detail :-)  Not an extremely coherent article.  The issue discussed doesn't appear to have much to do with length-of-year variations, per se.  Glad to see that Science (the journal) is making up their own minds on standard notations.  It seems pretty insipid to say that temperature and length don't have to worry about expressing the notion of "ago".

Rob
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On Jun 13, 2011, at 3:00 PM, Zefram wrote:


> Rob Seaman wrote:

>> If variation of length-of-year is a significant issue it has not been

>> stated previously in this context.

> 

> I think the issue there is not about *variation* in the length of

> year but about *which* year is referred to.  When referring to time

> rather than orbital mechanics, astronomers have traditionally used a

> unit called "year" defined as 31557600 s.  (That's based on the length

> of the Julian calendar year along with a nominal day of 86400 s, and

> of course no one claims that it precisely matches any Terran orbital

> parameter.)  Recently there's been some fuss about defining a similar

> time unit for use in other sciences, and the IUPAC (chemists) and IUGS

> (geologists) have jointly defined a unit called "annus" defined as

> 31556925.445 s.  (That's based on a measurement of the Terran tropical

> year somewhere around the year 2000, I'm hazy on the details.)  I read

> about it in New Scientist, <http://www.newscientist.com/article/

> dn20423-push-to-define-year-sparks-time-war.html>, and that has a

> reference to the IUPAC journal article.

> 

> It seems rather silly to me that (a) they would seek such precise

> agreement with a physical parameter that is, after all, context

> sensitive and slightly variable, and (b) they would ignore the very

> similar preexisting unit from astronomy.  That doesn't actually seem to

> be causing much controversy, though.  The main controversy seems to be

> that geologists object to the notation, where (for example) "1 Ga" now

> refers to a duration of 1 gigaannus, whereas preexisting geological usage

> has "1 Ga" refer to a *point in time*, a billion years before present.

> The geological usage is inconsistent with the principles of SI, and I

> think they had to face that sometime, but the symbol clash is moderately

> gratuitous.

> 

> -zefram