Daylight Hours Calculator NZ
This calculator works out how many hours of daylight there are at a given latitude on a given day of the year, along with the approximate times of sunrise and sunset. The length of the day changes through the year because the Earth's axis is tilted, so as our planet orbits the Sun, each hemisphere leans toward or away from it. In New Zealand that means long summer days around the December solstice and short winter days around June, with the swing growing larger the further south you go, from the milder seasonal change of the Far North to the marked difference felt in Southland. Knowing the day length is genuinely useful for planning tramping and outdoor trips, gardening, photography around the golden hours, energy use, and simply understanding the rhythm of the seasons. This tool calculates it from the underlying astronomy. You enter your latitude in degrees, negative for the Southern Hemisphere, so most of New Zealand sits between about minus 34 and minus 47, and the day of the year as a number from 1 to 365. The calculator works out the Sun's declination for that day and uses it with your latitude to find the length of daylight, then places sunrise and sunset symmetrically around solar noon. The results update as you type, so you can watch the day stretch and shrink across the year. Use it to compare the solstices, to plan around available light, or out of curiosity. Note that the times are solar and approximate, ignoring your exact longitude, time zone, daylight saving and the small effect of atmospheric refraction.
Approximate, using solar time around solar noon. Ignores longitude, time zone, daylight saving and refraction. Latitude is negative in the Southern Hemisphere.
How it works
The Sun's declination for the day is estimated from the date. Combined with your latitude, it gives the Sun's hour angle at sunrise and sunset through the standard daylight equation. The day length is twice that hour angle converted to hours, and sunrise and sunset are placed symmetrically before and after solar noon at 12:00.
Worked example
At latitude minus 41 degrees, near Wellington, on day 172 of the year, around the June solstice, the Sun's declination is about plus 23.4 degrees. The daylight equation gives roughly 9 hours and 3 minutes of daylight, with solar sunrise near 7:29 and sunset near 16:31, the short days of midwinter in the lower North Island.
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