Julian Day is defined as the number of days since noon UT on January 1, 4713 BC.
clc; clear all; % Input Date: April 11,2013. UT time 20:11:30 year = 2013; month = 4; day = 11; hour = 20; min = 11; sec = 30;
UT = hour + min/60 + sec/3600; J0 = 367*year - floor(7/4*(year + floor((month+9)/12))) ... + floor(275*month/9) + day + 1721013.5; JD = J0 + UT/24; fprintf('Julian Day = %6.4f [days] \n',JD)
Julian Day = 2456394.3413 [days]
Small Satellites 