A PUZZZLE FROM THE ALMANAC.

Manawatu Herald, Volume XLVIII, Issue 3511, 15 July 1926, Page 1

A PUZZZLE FROM THE ALMANAC.

A correspondent asks how it is that, according to the times given in the paper for sunrise and sunset, the longest day in December is 22 minutes longer than the longest night in June, says the “Post.” This follows (writes “Omega Centauri”) from the definition of sunrise and sunset which is adopted. The time of sunrise is the mean New Zealand civil time when the sun’s upper limb appears when the observer’s eye is 20 feet above sea level. According to the “New Zealand Nautical Almanac” refraction raises the •sun by more than half a degree, viz., 33 minutes 43 seconds. The dip of the horizon adds another 4 minutes 24 seconds. The centre of the sun is a further 16 minutes li seconds below the upper rim. The sum of these is reduced by 8£ seconds by the sun’s horizontal parallel. This makes the sun’s zenith distance at the moment of sunrise or sunset exceed a right angle by fifty-four minutes of arc. This naturally increases the length of the day and diminishes that of the night. We may say briefly that the discrepancy is caused by three factors, which, taken in the order of their importance, are: refraction, the use of the upper limb instead of the sun’s centre, and the dip of the horizon.