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From: Paul Hirose (no email)
Date: Mon Dec 01 2003 - 18:02:39 EST
Kieran Kelly wrote:
>
> 3) In your learned opinion what was the time of meridian passage on that day
> at long 132d 40' E.
I'll use MICA 1.52 again, but this time working the problem with local
hour angle rather than azimuth as I did earlier.
MICA doesn't seem to have a way to display local hour angles, so I
have to get tabulations of sidereal time and the Sun's right
ascension, then subtract one from the other.
SIDEREAL TIME
Location: E132ø40'00", S21ø48'18", 0m
(Longitude referred to Greenwich meridian)
Local App.
Date Time Sidereal Time
(UT1)
h m s h m s
2002 Jul 20 03:15:38.0 7 57 14.4944
2002 Jul 20 03:15:39.0 7 57 15.4972
2002 Jul 20 03:15:40.0 7 57 16.4999
Sun
Apparent Topocentric Positions
True Equator and Equinox of Date
Location: E132ø40'00", S21ø48'18", 0m
(Longitude referred to Greenwich meridian)
Date Time Right Ascension
(UT1)
h m s h m s
2002 Jul 20 03:15:38.0 7 57 15.607
2002 Jul 20 03:15:39.0 7 57 15.610
2002 Jul 20 03:15:40.0 7 57 15.613
The differences:
UT1 LAST-RA
03:15:38 23:59:58.9
03:15:39 23:59:59.9
03:15:40 00:00:00.9
Meridian passage occurs .1 s after the middle time, i.e., at
03:15:39.1 UT1.
On that date UT1 was .23 s behind UTC, so the UTC time was
03:15:39.3.
As I said before, on this date MICA overestimates the TT-UT1
difference by 3.6 seconds. So the Sun's UT1 position against the fixed
stars is computed for a time 3.6 seconds later than the correct time.
In 3.6 s its right ascension increases .01 s, so strictly speaking all
the RA's I tabulated above should be decreased by .01 s to put them on
the UT1 time scale. That's too small to worry about.
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