The March 2017 equinox happened on 20 March at 10:29 UTC.
By Jose Prieto (EUMETSAT)
Equinox literally means 'equal night', and it applies to each of two dates in the year of equal length of night and day. Due to atmospheric refraction, the day light is actually longer than 12 hours. In the Northern Hemisphere it is known as the Vernal (Spring) equinox and it is the Autumnal (Fall) equinox in the Southern Hemisphere.
At the equinox in March the Sun crosses the celestial equator from south to north, and it falls perpendicular on the Earth's equator. At a latitude of 50 degrees North, the Sun will reach then 40 degrees elevation at midday, with values increasing up to 63.4 degrees from now to 21 June.
The atmosphere does not react to astronomical ephemerides, but the Meteosat-10 Natural Colour RGB (top right, click to enlarge) shows at the moment of equinox a roughly symmetrical distribution of frontal structures in northern and southern hemispheres, with the inter-tropical convergence zone in the middle, as also described in the case study Atmosphere mirroring around the equator.
Note also that the ice over Greenland and over Antarctica is seen with similar contrast.
Video showing a satellite view of the sun's movement during the year. (Twitter/Simon Proud)
Animated equinox gif (Twitter/@bgreene)
March Equinox (timeanddate.com)