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

The Equinox


The 2017 Spring Equinox for the Northern Hemisphere (and Autumn in the South) will occur a few minutes after this post goes up. At an equinox, the Earth’s terminator—the dividing line between day and night—is at a right angle to the equator and connects the north and south poles. This time-lapse video show a view of a year on Earth in twelve seconds as seen from geosynchronous orbit by the Meteosat satellite. The video starts at the September, 2010, equinox. As the Earth revolves around the Sun, the terminator tilts in a way that provides less daily sunlight to the northern hemisphere during winter in the north. The March, 2011, equinox arrives halfway through the video, followed by the terminator tilting the other way during summer in the north. The year ends with the September, 2011, equinox.

Video Credit: NASA