How many seconds are in a year?

Question

How many seconds are there in a year? Do it in your head, rounding as you go, and then say why the answer is easy to remember. As a follow-up, use it to estimate how many seconds a person lives, and how many events happen in a year if they occur once per millisecond.

Accepted Answer

About 31.5 million (31,536,000 exactly for a 365-day year). The mental arithmetic. 60 seconds × 60 minutes = 3,600 seconds per hour. Times 24 hours: 86,400 seconds per day (a number worth memorising). Times 365 days: 86,400 × 365. Round it: 86,400 × 365 is about 86,000 × 365; 86,000 × 300 = 25.8 million and 86,000 × 65 = 5.6 million, total 31.4 million. The exact figure is 31,536,000. The coincidence. Pi times ten million is 31,415,927. So a year is very nearly pi times 10 to the 7 seconds, accurate to 0.4 per cent. Physicists use this constantly: "one year is pi times ten to the seven second…

How many seconds are in a year?

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