Explanation:
Welcome to an
equinox on planet
Earth.
Today is the first day of spring in our
fair planet's northern hemisphere,
fall in the southern hemisphere,
with day and night nearly equal around the globe.
At an equinox
Earth's
terminator, the dividing line between day and night,
connects the planet's north and south poles as
seen at the start of this remarkable
time-lapse
video compressing an entire year into twelve seconds.
To make it, the
Meteosat satellite recorded
these
infrared images every day at the same
local time from a geosynchronous orbit.
The video actually starts at the September 2010
equinox with the terminator aligned vertically.
As the
Earth revolves
around the Sun, the
terminator tilts to provide
less daily sunlight to the northern hemisphere, reaching the solstice
and northern hemisphere winter at the maximum tilt.
As the year continues, the terminator tilts back again and
March 2011 equinox arrives halfway through the video.
Then the terminator swings past vertical the other way, reaching the
the June 2011 solstice and
the beginning of northern summer.
The video ends as the
September equinox returns.
