Well, that's assuming that a year is exactly 365.25 days, which is consistent with the Julian Calendar--one leap year every four years. (13 x 365.25 x 24 = 113,958 hours) However, the Gregorian Calendar is the standard nowadays and this results in 3 fewer leap years in every 400-year cycle. (In recent times, the discrepancies occurred in the years 1700, 1800, and 1900.) Under this system, the average year would be precisely 365.2425 days, and 13 years would be 13 x 365.2425 x 24 = 113,955.66 hours. Of course, if we are interested in the actual 13-year period between a specific date and time in September of this year, 2007, and the same date and time in the year 2020, we would have to account for 4 leap years (2008, 2012, 2016, and 2020). Thus, our calculation would be ([13 x 365] + 4) x 24 = 113,976 hours.

Then, of course, we'd also have to account for any "leap seconds" that might be added during that 13-year interval. The precise number of such leap seconds is hard to predict at this pointâ€”it is empirically decided every year based on the discrepancy between a mean solar day and 24 x 60 x 60 = 86,400 standard seconds of time. We were doing approximately one leap second every year during the seventies, but there's been a drought of them during the last decade--only one has been added since 1999. I'm going to guess that things will pick up again and there will be 6 more leap seconds over the next 13 years. My best answer to this problem would then be 113,976 hours and 6 seconds.

## 1 Comments:

Well, that's assuming that a year is exactly 365.25 days, which is consistent with the Julian Calendar--one leap year every four years. (13 x 365.25 x 24 = 113,958 hours) However, the Gregorian Calendar is the standard nowadays and this results in 3 fewer leap years in every 400-year cycle. (In recent times, the discrepancies occurred in the years 1700, 1800, and 1900.) Under this system, the average year would be precisely 365.2425 days, and 13 years would be 13 x 365.2425 x 24 = 113,955.66 hours. Of course, if we are interested in the actual 13-year period between a specific date and time in September of this year, 2007, and the same date and time in the year 2020, we would have to account for 4 leap years (2008, 2012, 2016, and 2020). Thus, our calculation would be ([13 x 365] + 4) x 24 = 113,976 hours.

Then, of course, we'd also have to account for any "leap seconds" that might be added during that 13-year interval. The precise number of such leap seconds is hard to predict at this pointâ€”it is empirically decided every year based on the discrepancy between a mean solar day and 24 x 60 x 60 = 86,400 standard seconds of time. We were doing approximately one leap second every year during the seventies, but there's been a drought of them during the last decade--only one has been added since 1999. I'm going to guess that things will pick up again and there will be 6 more leap seconds over the next 13 years. My best answer to this problem would then be 113,976 hours and 6 seconds.

Uncle Bruce

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