Seconds since 1980Date: 08/08/2002 at 09:51:06 From: Bob Subject: Seconds since 1980 Hi there, How can I work out the number of seconds since 1980, taking leap years into account? Stuck as anything - please help, Regards, Bob G Date: 08/08/2002 at 11:03:12 From: Doctor Ian Subject: Re: Seconds since 1980 Hi Bob, It's more complicated than that; you have to take leap _seconds_ into account as well. (Every so often, we have to add or subtract a second to account for changes in the earth's rotational period.) But basically, the conversion looks like this: seconds past 1980 = (days since 1 Jan 1980) * 86400 + (hours since midnight) * 3600 + (minutes past the hour) * 60 + (seconds past the minute) + (leap seconds) To find the number of days, you can do this: days since 1 Jan 1980 = (current year - 1980) * 365 + (current day of year - 1) + (1 leap day for 1980, 1984, 1988, 1992, 1996, 2000, 2004, and any other leap years that have passed) Here is a table, through 1999, of the leap seconds accumulated by date: Leap seconds Date ------------ ---------- 19 1980-JAN-1 20 1981-JUL-1 21 1982-JUL-1 22 1983-JUL-1 23 1985-JUL-1 24 1988-JAN-1 25 1990-JAN-1 26 1991-JAN-1 27 1992-JUL-1 28 1993-JUL-1 29 1994-JUL-1 30 1996-JAN-1 31 1997-JUL-1 32 1999-JAN-1 According to the USNO Web site, no new leap seconds have been added since 1999, but you can always get an up-to-date listing from the NAIF Project at NASA/JPL: http://naif.jpl.nasa.gov/naif.html In fact, if you plan to be doing this kind of thing with any regularity, you should probably download a copy of their toolkit. You'll also need to convert from your local time to Greenwich Mean Time before doing the conversion! I hope this helps. Write back if you'd like to talk more about this, or anything else. - Doctor Ian, The Math Forum http://mathforum.org/dr.math/ |
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