This utility can convert a gregorian date into julian day format/Modified Julian Day format and vice versa. The Julian Day Format counts the day since the 24th november -4713bc. The julian day format is often used in the astronomical section to calculate for example rises. This utility offers a fast and easyway to convert a gregorian date information to a julian day format or modified julian day format. The Modified Julian Day (MJD), introduced by the Smithsonian Astrophysical Observatory in 1957 to record the orbit of Sputnik, is defined in terms of the Julian day. It count the days since the 17th november 1858. It defines from the JD value as follow MJD =JD-2400000