My solution to: “How much extra daylight per day?”

Before I show you the somewhat imprecise method I used to arrive at this result, I want to remind you that the challenge was to work out the amount of extra daylight we get here in Nova Scotia per day between the winter and summer equinoxes, using only this ‘sun graph’ from (but NOT the data table below it!) . Why? Because “everybody loves the sunshine” and I fricking love this graph!:

Sun Graph from for Halifax, Nova Scotia

NB: If you look down on the very same page you will also find tables of sunrise & sunset data for each month, from which you can easily calculate your daily ration of extra daylight pretty accurately, and check the value you found for the average amount.

Working out the summer equinox daylength
Finding approximate location of winter equinox 21st Dec.

My Method

  • I loaded the sun-graph into Geogebra.
  • Located the approximate position of the summer equinox (2 thirds of the way from June to July on the horizontal axis
  • I placed points at the top and bottom of the vertical axis, to enable me to measure the vertical size of the graph.
  • I put another pair of points at the top and bottom of the daylight portion, so I could measure that.
  • I compared the length of DE to that of CF (24 hours): so daylength = 24 x DE/CF
  • Daylength = 24 x 2.53/3.86 = 15.73 hours (LAtex would look better!) I did the same for the winter equinox, 21st December giving me: daylength = 24 x 1.42/3.87 = 8.81 hours
  • I found the difference in the daylength for the equinoxes: 15.73 – 8.81 = 6.92 hours
  • Divided total difference by the number of days in half a year: 6.92 / (365/2) = 0.0379 hours per day
  • Put this into a more helpful unit (seconds!): 0.0379 x 60 = 2.275 mins per day
  • Converted 0.275 minutes to seconds: 0.275 x 60 = 16.5 seconds

My answer: we get on average 2 minutes and 17 seconds per day of extra daylight

What answer did you get? Write a comment below to share or ask for help.


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