NavList:

   

Reply

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:  E132?40'00", S21?48'18",     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:  E132?40'00", S21?48'18",     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.

   

Reply