The MJD60K problem.

[Dr Paul Leyland]

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

[Nick James]

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.

[Dr Paul Leyland]

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.

• This reply was modified 1 year, 9 months ago by Dr Paul Leyland. Reason: Fix BBCode tags
• This reply was modified 1 year, 9 months ago by Dr Paul Leyland.
• This reply was modified 1 year, 9 months ago by Dr Paul Leyland.
• This reply was modified 1 year, 9 months ago by Dr Paul Leyland.

[Dr Paul Leyland]

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.

• This reply was modified 1 year, 9 months ago by Dr Paul Leyland.
• This reply was modified 1 year, 9 months ago by Dr Paul Leyland.

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