Explanation: Can you tell that today is a solstice by the tilt of the Earth? Yes. At a solstice, the Earth's terminator -- the dividing line between night and day -- is tilted the most. The featured time-lapse video demonstrates this by displaying an entire year on planet Earth in twelve seconds. From geosynchronous orbit , the Meteosat 9 satellite recorded infrared images of the Earth every day at the same local time . The video started at the September 2010 equinox with the terminator line being vertical: an equinox. As the Earth revolved around the Sun, the terminator was seen to tilt in a way that provides less daily sunlight to the northern hemisphere, causing winter in the north. At the most tilt , winter solstice occurred in the north , and summer solstice in the south. As the year progressed, the March 2011 equinox arrived halfway through the video, followed by the terminator tilting the other way , causing winter in the southern hemisphere -- and summer in the north. The captured year ends again with the September equinox , concluding another of the billions of trips the Earth has taken -- and will take -- around the Sun.

APOD Review: RJN's Night Sky Network Lecture