A Day or So After the Summer Solstice

According to the US Naval Observatory, the Sun will rise on June 23 2014 at 05:27 Central Daylight Time (CDT) and will set at 21:04 CDT. From now on, days will be shorter. How long will the day be?

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Answer: The times are given on a 24-hour clock. 21:04 is the same as 9:04 PM on a 12-hour clock. Note that the colon : is not a decimal point. Minutes, to the right of the colon, are base 60. For example, 5 minutes after 20:59 is 21:04. Hours, to the left of the colon, are base 12 or base 24. For example, 1 hour after 23:30 is 00:30.

We need to subtract 05:27 from 21:04. You can't take 27 from 04, so you "borrow" an hour from 21. When it crosses the colon, 1 hour becomes 60 minutes and 21:04 becomes 20:64. Now subtract 27 from 64 and get :37 and subtract 5 from 20 and get 15. The day is 15 hours and 37 minutes long.

Challenge: How long is the night?

Later in the month, we should expect the days to get shorter and nights to get longer.