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Date, Time and the Sun? The Sun is the basis of our Time!

My simpleLib sDatTimeSun.h library. All possibilities at a glance (see the red dots).

Time (interval) synchronization from NTP time servers (use my sWiFiFull.h) or user/RTC input.
In addition to the standard usage options for date, time and sun, you can also control a Sun Tracker with SunRise/Set and SolPos. For example, a solar parabool, solar panel, sun following tubular daylighting or, go crazy, a sundial with a pointer instead of shadow.

Use my sDateTimeSun.h library examples as a guide!
HINT: Combine it with my sWiFiFull.h library examples with these selectable options:

 sDateTimeSun.h library examples:
  sTime.ino         (included: UTC, Local, Zone, DST and Sun Rise/Set)
  sTimeCalc.ino     (some of the many possibilities)
  sTimeM5Stick.ino  (see M5 image above, also usable with other modules and displays)
  sEquiSol.ino      (Equinox: March, September / Solstice: June, December)
  sSolPos.ino       (lat: 52.09, lon: 5.13, 6 dec 2018 12:00: azi: 172.71°, alt: 15.16°)
User date names and calendar options:
Standard English but you can set your own language and calendar options in void setup().
Calendar options: first week of the year and first day of the week.
void sSetWeek(const char _wk = _week); // change strftime week code
sSetWday(const char _wd = _wday); // change strftime weekday code
sSetMonthDayStr(const char _mL[12][21], const char _mS[12][11], const char _dL[7][21], const char _dS[7][11]); // change long and short month and day names
Date, Time and Sun functions:
(Structures after the functions)
void       sSetTz(char* tz); // set Time Zone
sGetNTP(char * _timeZone); // get time from server
sSetEpoch(sEpoch _ep); // set time manual, use sMakeTime() uint64_t sTimestampInt(sEpoch _ep = sEp); // timestamp in milliseconds // if _ep NULL then the current time is used
sTimestampStr(sEpoch _ep = sEp); // timestampString in milliseconds
// if
_ep NULL then the current time is used
sEpoch sMakeTime(int64_t _msec); // time from a timestamp in milliseconds
sEpoch sMakeTime(int8_t h, int8_t m, int8_t s, int16_t ms, int8_t D, int8_t M, int16_t Y); // calc a timesEpoch sNow(sEpoch _ep = sEp); // current time or current time +/- t-offset in seconds
// if
_ep NULL then the current time is used
sEpoch sAbsDiff(sEpoch _epX, sEpoch _epY = sEp); // absolute difference between _X and _Y
// if
_epY NULL then the current time is used
sSMHD sTimeSplit(time_t t); // split a seconds time in days, hours, minutes and seconds
sDateTime sTimeDate(bool _gmt, sEpoch _ep = sEp); // get a set of local/gmt time and date values
// if
_ep NULL then the current time is used
now(time_t t = 0); // as ep.sec from sEpoch ep = sNow();
// if
t NOT NULL then then t is a +/- offset to the current time // time_t t = now(12*60*24); // t = tomorrow at the same time
/** get GMT + zone + dst **/ // if
t NULL then the current time is used else t is used
year(time_t t = now());
month(time_t t = now());
day(time_t t = now());
hour(time_t t = now());
minute(time_t t = now());
second(time_t t = now());
weekday(time_t t = now());
yweek(time_t t = now());
yday(time_t t = now());
/** get GMT **/
// if
t NULL then the current time is used else t is used
yearGmt(time_t t = now());
monthGmt(time_t t = now());
dayGmt(time_t t = now());
hourGmt(time_t t = now());
minuteGmt(time_t t = now());
secondGmt(time_t t = now());
weekdayGmt(time_t t = now());
yweekGmt(time_t t = now());
ydayGmt(time_t t = now());
sRiseSet sSun(time_t t, double lat, double lon, bool gmt = false); // calc rise and set times bool sDaylight(time_t t, sRiseSet rs); // is it sun down time sEquiSol sCalcEquiSol(uint16_t Y); // Equinox and Solstice calculation: // spring, summer, autumn, winter (as UTC/GMT time) sSolPosOut sSolPos(sSolPosIn _sp); // Calculates the True North location of the Sun in the sky // for any given location, day, and time. // Valid from the year 1950 to 2050
The used Structures:
struct sEpoch { // timestamp and milliseconds
  time_t  sec;        // UNIX timestamp
  int16_t msec;       // milliseconds 000-999
struct sRiseSet { // output: SunRise and SunSet local or UTC
  time_t  rise,       // SunRise local or UTC
          set;        // SunSet local or UTC
struct sEquiSol {     // output: Equinox and Solstice (as UTC/GMT time)
 sEpoch   spring,     // Equinox, March
          summer,     // Solstice, June
          autumn,     // Equinox, September
          winter;     // Solstice, December
/************ position of the Sun (Solar tracker) ************/
// use it in combination with SunRise and SunSet from "sRiseSet sSun(...)"
struct sSolPosIn { // input: True North location of the Sun in the sky
  time_t  time;       // local time
  double  temp,       // you can get it with my sOpenweathermap.h lib.(free key on 
                      //    "http://api.openweathermap.org/data/2.5/weather?")
          pres,       // you can get it with my sOpenweathermap.h lib.
          zone,       // seconds: use "sDateTime.offset" or a "local-UTC" time
          lat,        // location North/South parallel to the Equator 
          lon;        // location East/West of the 0°Prime Meridian
                      //    (The meridian of the British Royal Observatory in Greenwich)
struct sSolPosOut {   // output: True North location of the Sun in the sky
  double  azimuth,    // the angle of the sun around the horizon, usually measured from
                      //    true north and increasing eastward
          altitude;   // the angle between the sun and the observer's local horizon
struct sDateTime { // local/UTC time and date
            // set by function: sDateTime sTimeDate(bool _gmt, sEpoch _ep)
  time_t  sec;        // UNIX timestamp (it's a int32_t)
                      //    GMT < 0, MIN: 13 December 1901 20:45:52
                      //    GMT == 0, : 1 January 1970 00:00:00
                      //    GMT > 0, MAX: 19 January 2038 03:14:07
  int8_t  second,     // seconds 00-59
          minute,     // minutes 00-59
          hour,       // hours 00-23
          day,        // day 01-31
          month,      // month 01-12
          week,       // week 01-53
          wday;       // weekday 1-7
  int16_t msec,       // milliseconds 000-999
          year,       // year 1901-2038
          yday;       // yearday 001-366
            // timezone and DST
  time_t  zone,       // seconds
          dst,        // seconds
          offset;     // zone + dst (sec - offset = UTC/GMT)
            // Long/Short month/day names
  char    monthL[21], // month Long name
          monthS[11], // month Short name
          dayL[21],   // day Long name
          dayS[11];   // day Short name
struct sSMHD { // split timestamp to time and days
            // set by function: sSMHD sTimeSplit(time_t _t)
  int8_t  seconds,    // seconds 00-59
          minutes,    // seconds 00-59
          hours;      // hours 00-23
  int16_t days;       // days 0-n