Hi Art,
Re your rhetorical:
>You just wanted me to say "literal equinox"?
No, I just wanted to pass on something I learned when I
computed the time at zero declination in an attempt to
get the Autumnal Equinox value for 1997 in connection with
Bart's wedding query. When I compared my result with
almanac values I found a discrepancy and looked into the
cause of it. When I found that my, and your, operational
definition was not that conventionally used by astronomical
almanac preparers, I thought, "live and learn, maybe Carlson
would be interested in this, since he used zero declination
too." Your next response suggested that, indeed, the idea
was new to you also:
>I see the possibility and usefulness of defining an
>equinox direction in addition to an equinox time. Thanks
>for pointing this out. The terminology is unhappily chosen
>when "true" = "apparent" =/ "literal".
>I'm struggling to understand this. Does this mean that
>astronomical almanacs always start at the vernal equinox
>and are good for one year? Or rather for one year minus
>(or plus?) 20 minutes (or 40?). Would the almanac valid
>for the previous year put the sun at the First Point of
>Aries 20 minutes earlier that the almanac valid for the
>followingyear?
Rather than hazard the "death of many questions", I'll cite
some data. The almanacs for 1988 through 1992 (five that I
happen to have at hand on my study shelves) list the UCT of
the Vernal Equinox (in March) at Greenwich as I've tabulated
below. They at least hint at some answers:
______________________________________
| | | | | Diffs. |
Year | Day |Date| h | m |-----|----|
-----|------|----|----|----| h | m |
1988L| Sun. | 20 | 09 | 39 |-----|----|
-----|------|----|----|----|} 05 | 39 |
1989 | Mon. | 20 | 15 | 18 |-----|----|
-----|------|----|----|----|} 05 | 01 |
1990 | Tue. | 20 | 21 | 19 |-----|----|
-----|------|----|----|----|} 05 | 43 |
1991 | Wed. | 21 | 03 | 02 |-----|----|
-----|------|----|----|----|} 05 | 46 |
1992L| Fri. | 20 | 08 | 48 |-----|----|
-----|------|----|----|----|
("L" designates leap year.)
>From all of this, I find your comment apposite:
>This seems like a strange way to do business, but then the
>whole business of astronomy seems to be getting
>incommensurate definitions to coexist (like leap years).
Yes, the "music of the spheres" does not comprise harmonic
structure in simple small-integer ratios. One might say,
"the fault is not in ourselves, but in the stars", still,
this seems a poor sort of tune we are rehearsing for Bart's
prospective epithalamium.
Cheers,
Bill.
--
To publish, to study, to retract.- Anonymus Bosh
