The MJD60K problem.

Forums General Discussion The MJD60K problem.

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  • #615921
    Dr Paul Leyland
    Participant

    OK, hands up all those whose software has broken because the MJD (Modified Julian Date) flipped from 59999 to 60000 yesterday.

    As far as I know, all my code is MJD60K clean but can’t vouch for everything I use which has been written by others.

    If anything has broken I’ll report here so that others may also take action if they wish.

    Paul

    #615923
    Nick James
    Spectator

    It would have to be rather weird software since I would think that MJD would almost always be stored as a double. I suppose in some odd cases it might be stored as an uint16_t but then it would break at 65536, not 60000 and I have no idea why anyone would do that.

    #615924
    Dr Paul Leyland
    Participant

    It is not just a matter of storage. For instance, some years ago one of my Perl scripts contained this

        my ($star, $jd, $mag);
        while (<INPUT>) {
            if (/^Variable\s+(.*)/) {
                $star = $1 and next;
            } elsif (/^(245\d+\.\d+)\tV\t(.*?)\t/) {
                ($jd, $mag) = ($1, $2);
                $mag =~ s/\[/</ or $mag = sprintf “%.2f”, $mag;
                my ($year, $month, $day) = jd2gregorian ($jd + 0.5);
                printf “%s\t%.3f\t%s\tLEY\n”, $star, $day, $mag;
            }
        }
    

    Spot the bug.

    #615929
    Dr Paul Leyland
    Participant

    I remember a similar Y2K bug in a clock display. The coder appended the year to “19”, rather than adding to 1900. On 2000-01-01 the display read 1 Jan 19100.

    Takeaway message: character strings are not numbers, even when they look like them.

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