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Full Version: computing the time of the seasons with the HP Prime
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This HP Prime program uses several of the routines already provided in this forum to compute the time of the seasons; spring equinox, summer solstice, fall equinox and winter solstice.

The user can edit the program and provide a calendar year of interest. The software computes the calendar date and Universal Coordinated Time (UTC) of each celestial event. Here are the program results for 2016. The UTC is typically within 10 minutes of the time computed with a precision solar ephemeris. The local civil time of an event at a particular geographic location is a function of the time zone and the status of daylight savings time (DST) at that location.

time of the equinoxes and solstices

SPRING EQUINOX

calendar date Mar 20, 2016

UTC time 4 hr 20 min 53.088 sec

SUMMER SOLSTICE

calendar date Jun 20, 2016

UTC time 22 hr 25 min 28.704 sec

FALL EQUINOX

calendar date Sep 22, 2016

UTC time 14 hr 11 min 14.496 sec

WINTER SOLSTICE

calendar date Dec 21, 2016

UTC time 10 hr 34 min 24.384 sec

This program uses several routines slightly modified for this application. In the zip collection, they are brent_equsol, sun_equsol and esfunc. A PDF document explaining the basic algorithm is also provided.
Updated version. All source code in one single file so that global variables are available.
The attached zip file contains an updated HP Prime program for computing the time of the seasons. It uses the precision solar ephemeris posted earlier on this forum. The fundamental time argument for the ephemeris has also been changed to Barycentric Dynamical Time (TDB).

Here is the program output for the example included in the attached PDF document.

time of the equinoxes and solstices

SPRING EQUINOX

calendar date Mar 20, 2013

UTC time 11 hr 1 min 31.296 sec

SUMMER SOLSTICE

calendar date Jun 21, 2013

UTC time 5 hr 3 min 47.808 sec

FALL EQUINOX

calendar date Sep 22, 2013

UTC time 20 hr 43 min 49.728 sec

WINTER SOLSTICE

calendar date Dec 21, 2013

UTC time 17 hr 10 min 51.168 sec
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