On 5 Aug 2005 at 10:16, Mark Calabretta wrote:
> The fiction that there are 86400 "seconds" in a solar day is part
> of the problem - noone uses the word "second" in this context.
On Aug 4, 2005, at 5:45 PM, Daniel R. Tobias wrote:
> Actually, I'd say that more people use the word "second" in this
> context than do in the scientifically accurate context of the SI
> definition. To the "man/woman on the street", a second is 1/60 of
> a minute, a minute is 1/60 of an hour, and an hour is 1/24 of a day,
Precisely. Civil time is not the same as scientific time.
As Steve Allen has pointed out, it is unfortunate that we have
allowed them to be expressed in similar sexigesimal fashions. A
sexigesimal string is really just the representation of a number. As
we all learned in school, whenever a number is quoted the units
should also be expressed. Our problem is that we permit - nay,
encourage - time to be expressed without units, as if it were some
Platonic ideal. But time means different things in different
contexts (even ignoring Einstein completely) - and the dictionary
definition of the word "second" does include multiple meanings even
within the realm of time.
We live in interesting times. When I'm not being peeved by the leap
second wars, I'm grateful for the opportunity it has provided to
investigate all sorts of intrinsically fascinating subjects. But
leap seconds are thankfully not the only game in town, and we find
ourselves with a revived manned space program and the discovery of a
new planet all in the same week. I'd encourage folks to read the
original announcement of Planet Claire (or whatever they are going to
call it):
http://www.gps.caltech.edu/~mbrown/planetlila
Personally, I hope the scientific data security issues discussed at
the bottom of the page aren't a harbinger of a whole new class of
hacker attacks. But then, astronomers have been dealing with the
threat of scientific espionage and proper crediting of discoveries
since Galileo's day.
The discovers of this new spectacular Kuiper Belt Object (KBO) raise
the issue of its proper classification:
> Is this object really a planet? Is Pluto a planet? What makes a
> planet?
>
> Even after all of these years of debate on the subject of whether
> or not Pluto should be considered a planet, astronomers appear no
> closer to agreement. [...] Culturally, however, the idea that
> Pluto is a planet is enshrined in a million different ways. [...]
> The word "planet" has been around much longer than modern science.
>
> From now on, everyone should ignore the distracting debates of the
> scientists, and planets in our solar system should be defined not
> by some attempt at forcing a scientific definition on a thousands-
> of-years-old cultural term, but by simply embracing culture. Pluto
> is a planet because culture says it is.
The fact is that Pluto is not just a planet - scientifically it is
clearly also a KBO. We are currently waiting for the International
Astronomical Union (IAU) to declare whether the new, even larger, KBO
is itself to be considered a planet or not. This will be an
interesting debate - but ultimately, it will be the larger culture
that will determine the answer. Pluto is a planet because your kid's
placemat says it is. Will the new, more distant, object receive
similar cultural respect? This could key on something as simple as
whether they picked a memorable name like "Claire" or "Lila".
A second is one sixtieth of a minute, which is one sixtieth of an
hour, which is one twenty-fourth of a solar day because that is what
six billion people think. That a second is also some obscure SI
definition might be of interest to folks with an oversize volume from
the CRC Press on their shelf - but this is certainly not the most
frequently relied upon definition for the word "second" even when
restricted to its meaning(s) as a unit of time.
It is fact, not fiction, that there are 86400 seconds per solar day.
It is also a fact that a second has a precise SI definition. Which
is more real? The obvious definition as a fraction of a solar day -
rubber seconds and all? Or the obscure definition that I challenge
anybody to recite without aid from the Chemical Rubber Company? And
is it better to resolve this ambiguity by pretending that these two
equally important definitions are identical - or by admitting that
they are quite distinct?
Rob Seaman
National Optical Astronomy Observatory
Received on Fri Aug 05 2005 - 10:08:00 PDT