Spring Has Sprung …

… here in the Northern Hemisphere. The equinox occurred last week. At an equinox Earth’s terminator, the dividing line between day and night, runs through the planet’s north and south poles as seen at the start of this time-lapse video which crams an entire year into twelve seconds. It was put together using Meteosat infrared images taken every day at the same local time from a geosynchronous orbit. The video actually starts at the September 2010 equinox. As the Earth revolves around the Sun, the terminator tilts as less daily sunlight falls on the northern hemisphere, reaching the solstice and northern hemisphere winter at the maximum tilt. As the year continues, the terminator tilts back again to the March 2011 equinox halfway through the video. Then the terminator swings past the poles, until the June 2011 solstice, the start of northern summer. The video ends as the September equinox returns.

Video Credit: NASA / Meteosat / Robert Simmon

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