[time-nuts] Equinox and sidereal time

Tim Shoppa tshoppa at gmail.com
Mon Mar 24 13:02:34 EDT 2014


I think this sort of table is what you want, right? Vernal equinox is when
sun passes through zero point of right ascension.

I made this online at http://aa.usno.navy.mil/data/docs/geocentric.php

Astronomical almanac has coarser tables and constants/instructions for
interpolating.

I think the constants used by the USNO's PHP scripts, must come straight
from astronomical almanac.

                                    Sun

                       Apparent Geocentric Positions
                     True Equator and Equinox of Date

   Date        Time          Right       Declination     Distance     Equation
        (UT1)              Ascension                                   of Time
             h  m   s     h  m   s         °  '   "         AU          m   s
2014 Mar 20 16:57:00.0   23 59 59.981   +  0 00 00.12   0.995914409   - 7 24.6
2014 Mar 20 16:57:01.0   23 59 59.984   +  0 00 00.14   0.995914412   - 7 24.6
2014 Mar 20 16:57:02.0   23 59 59.987   +  0 00 00.16   0.995914416   - 7 24.6
2014 Mar 20 16:57:03.0   23 59 59.989   +  0 00 00.17   0.995914419   - 7 24.6
2014 Mar 20 16:57:04.0   23 59 59.992   +  0 00 00.19   0.995914422   - 7 24.6
2014 Mar 20 16:57:05.0   23 59 59.994   +  0 00 00.21   0.995914426   - 7 24.6
2014 Mar 20 16:57:06.0   23 59 59.997   +  0 00 00.22   0.995914429   - 7 24.6
2014 Mar 20 16:57:07.0   23 59 59.999   +  0 00 00.24   0.995914432   - 7 24.6
2014 Mar 20 16:57:08.0    0 00 00.002   +  0 00 00.25   0.995914435   - 7 24.6
2014 Mar 20 16:57:09.0    0 00 00.004   +  0 00 00.27   0.995914439   - 7 24.6
2014 Mar 20 16:57:10.0    0 00 00.007   +  0 00 00.29   0.995914442   - 7 24.6
2014 Mar 20 16:57:11.0    0 00 00.009   +  0 00 00.30   0.995914445   - 7 24.6
2014 Mar 20 16:57:12.0    0 00 00.012   +  0 00 00.32   0.995914449   - 7 24.6
2014 Mar 20 16:57:13.0    0 00 00.014   +  0 00 00.34   0.995914452   - 7 24.6
2014 Mar 20 16:57:14.0    0 00 00.017   +  0 00 00.35   0.995914455   - 7 24.6
2014 Mar 20 16:57:15.0    0 00 00.019   +  0 00 00.37   0.995914458   - 7 24.6
2014 Mar 20 16:57:16.0    0 00 00.022   +  0 00 00.39   0.995914462   - 7 24.6
2014 Mar 20 16:57:17.0    0 00 00.025   +  0 00 00.40   0.995914465   - 7 24.6
2014 Mar 20 16:57:18.0    0 00 00.027   +  0 00 00.42   0.995914468   - 7 24.6




On Sun, Mar 23, 2014 at 7:02 PM, Neville Michie <namichie at gmail.com> wrote:

> Hi,
> can anyone out there point me to a source
> for the exact time of the equinoxes and solstices
> so that I can synchronise a sidereal clock?
> I assume that at some time the Universal Time we use
> is exactly the same as Sidereal time, and so a Sidereal clock
> could be set.
> I have a Tbolt producing 10MHz, and divide it with one of Tom's
> excellent PICDIV chips, to get sidereal seconds. I would like to
> be able to hear them ticking away as I follow a star with a theodolite,
> and check my local time and position.
> If I use published times for the equinox, to one minute, I only get
> about 0.2 second resolution.
> There is probably more to this than meets the eye, but where does one
> find out about it?
> cheers,
> Neville Michie
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