This file is from Wikimedia Commons and may be used by other projects.
The description on its file description page there is shown below.
Summary
DescriptionHours of daylight vs latitude vs day of year cmglee.svg
English: A contour plot of the hours of daylight as a function of latitude and day of the year, using the most accurate models described in Sunrise equation, based on http://commons.wikimedia.org/wiki/File:Hours_of_daylight_vs_latitude_vs_day_of_year.svg . Latitude 40° N (approximately New York City, Madrid and Beijing) is highlighted for reference.
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.