Vernal Equinox – 20th March 2014

Illumination of the Earth during an equinox. Image Credit: http://en.wikipedia.org/wiki/File:Earth-lighting-equinox_EN.png

Today at 16:57 UT sees the Northward equinox.  For ourselves in the Northern Hemisphere, it is known as the Vernal or Spring equinox and the Autumnal equinox for residents in the Southern Hemisphere.

The Sun falls on the Celestial Equator during the Vernal equinox resulting in equal lengths of day and night across the planet.  From today on-wards  as the name suggests, the Sun is seen to be moving northwards, resulting in longer days and shorter nights for us.

The Celestial Sphere. Image credit: http://www.kirchdorferweb.com

The point on the Celestial Equator where the Sun lies during the Vernal equinox is known as the First Point of Aries.  However, due to precession (the continued change in the rotation of the planet on its axis), the Sun is no longer in the constellation of Aries and hasn’t been since around 100 BC.  At the moment, the Sun is in the constellation of Pisces and by the year 2600 it will be in the neighbouring constellation of Aquarius.

As the Sun rises at an equinox, the Sun will appear to cross the horizon due east and recrosses the horizon at Sunset due west.  Over the next 3 months leading up to the Summer or June Solstice, the Sun will appear to rise and set further to the north of these points as it appears to follow the path of the ecliptic.  It will then move back south approaching the southward or autumn equinox in September when the Sun will again rise and set due east and west respectively.

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