John Cowan wrote:
MAPS: In general the flybys around T20 are relatively similar. They
approach over 35degrees latitude, ~135degrees west longitude
(moving from north to south) and local time is around 2 am.
Bizarre. So each Titan local day is 24 local hours long, where an
hour
is about 57.4 ksec?
Which of these notions would you prefer to discard – the idea that
local planetary time is divided into 24 parts, or that one of those
parts may not be 3600 SI seconds long? In a solar system full of
dozens of rotating spheroids, what overarching concept of timekeeping
best ties all the local clocks together? Oh! I know – let's ignore
the big shiny signpost in the middle! Surely every space mission
isn't tasked with inventing not only a new clock, but also a new kind
of clock? Surely it would be better to adapt prior art to new
conditions?
On this tidally locked moon, one can make the case that descriptors
like midnight, noon, sunrise and sunset gain an even greater
importance precisely because they are extended by a factor of 16 in
duration. How then best to convey an illumination similar to 2 am
local time on Earth, rather than by calling it "2 am"?
Should the Earth be deemed a special case whose rotational clock will
be allowed to drift by 54,000 arcseconds precisely over the
historical period that humanity is exploring, visiting and perhaps
colonizing other planets and moons? Why?
My personal mnemonics: you can be no more than a ksec late for an
appointment in American culture without anyone making a fuss; a
Msec is
a reasonable length of time for a single work assignment; a
marriage is
doing very well if it lasts a Gsec (mine is at 0.85 Gsec and
counting).
And any good university library will be chock-a-block with utopian
screeds for metric calendars and clocks.
Presumably folks who dismiss sexagesimal Sumerian units for clocks
would also welcome the deprecation of degrees for measuring angles.
So the Cassini operations staff would be expected to report its
ground track as 0.6108N 2.356W, and local time (since this is an
angle, too) as 0.5236 radians past midnight? I prefer my pi cut into
12 slices.
The pragmatic engineers who pilot spacecraft pay little attention to
astronomers' whims when choosing what standards to use. They must
have had some other reason for not specifying those "standard" units
that were baptized during the Reign of Terror.
Rob
