# Short Julian day

Short Julian day is the same as Reduced Julian Day and Modified Julian day
^{[1]}
and refers to scale of time, related with rotation of orientation of the Earth with respect to Sun.

Short julian days are related to date, expressed with year.mo.da. At least since 1858.11.16, the short Julian day is positive, and is related to the convencional civil data with the simple algorithms copypasted below:

## Contents

## From Short Julian day to date

void ju24da(int Mjd, int *Year, int *Month, int *Day)

{ int J, C, Y, M;

J = Mjd + 2400000 + 68569;

// J = Mjd + 2400001 + 68569;

// J = Mjd + 68569;

C = 4 * J / 146097;

J = J - (146097 * C + 3) / 4;

Y = 4000 * (J + 1) / 1461001;

J = J - 1461 * Y / 4 + 31;

M = 80 * J / 2447;

*Day = J - 2447 * M / 80;

J = M / 11;

*Month = M + 2 - (12 * J);

*Year = 100 * (C - 49) + Y + J;

// http://www.leapsecond.com/tools/gpsdate.c

}

## From date to Short Julian day

int daju24(int Y,int M, int D)

{ int a, y,m;

a=(14-M)/12;

y=Y+4800-a;

m=M+12*a-3;

// return D + (153*m+2)/5 +365*y + y/4 - y/100 + y/400 -32045 - 2400001;

return D + (153*m+2)/5 +365*y + y/4 - y/100 + y/400 -32045 - 2400000;

}

## Julian day

Usually, the Julian day is used instead of the Short Julian day. At least for positive values of the Short Julian day, denoted with SUD, the Julian day can be expressed as follows:

Julian day = SUD + 2400000

Short Ulian day is easier to copy past for those persons, who can count 5 digits, but may fail, counting 7 digits..
In additoin, SUD may have also nevative values, and the simple formulas in the algorithms above hold.
As for the Julian days, for small and negative values, the results by the algorithms above differ from those, suggested by the public service
^{[2]}^{[3]}.

The main purpose of the Short Julian day is the same as that of the conventional Julian day, namely, calculation of time interval between given data and calculation of date after given number of days since the given data.

There are many various modifications of the Julian days, but, perhaps, in TORI, Short Julian days will be used.

## References

- ↑ http://www.csgnetwork.com/julianmodifdateconv.html Modified Julian Day Converter
- ↑ http://www.nr.com/julian.html?delta=++240000 Julian Day and Civil Date Calculator
- ↑ http://aa.usno.navy.mil/data/docs/JulianDate.php Julian Date Converter

http://en.wikipedia.org/wiki/Julian_day