Daylight Hours, Timeline
This Google Earth time animation is a simplified visualization of the how number of daylight hours (insolation duration) varies according to latitude over one year.
Each 5-day step of the animation displays a series of coloured bands. Boundaries between these bands are isochrones, representing whole numbers of daylight hours, 0 – 24. The Black and Yellow regions at the poles correspond to perpetual night and daylight.
Calculations are approximate, and decrease in accuracy away from the Equator and Prime Meridian. For comparison I recommend checking out the tables on the U.S. Naval Observatory website.
- To view the timeline, simply download the file and hit play
- Transparency may be altered by highlighting the Overlays folder, and using the transparency slider.
At faster speeds, on looped playback, the effect of the animation is quite hypnotic. Might not be a good idea to stare at it for too long. 😉
Basic outline of how the file was created:
– I generated the KML with a Perl script. Iterating Sunset and Sunrise time functions to find latitudes for integer hour values.
– The 26 bands displayed in each time span are a contiguous series of single colour, image overlays.
– Every overlay uses the same, 2×2 pixel jpeg, stretched around 360 degrees longitude. KML’s <color> tag assigns the colour.