Today (20th March) is a rather special day. At 05:31 this morning the sun crossed directly over the equator, which may not sound like a big deal but it was at this point that the vernal equinox occurred, the moment that all over the world the length of the day was equal to the length of the night. For us folks in the Northern Hemisphere our days will gradually increase in length compared to our nights right up to the summer solstice on June 23rd when the day time is at its maximum. For those in the Southern Hemisphere the opposite is occurring, at 05:31 this morning they had they autumnal equinox, day and night are still the same length, but it is the nights which are gradually getting longer right until the winter solstice which occurs also on June 23rd, when in the southern hemisphere, night time is at its longest.
What does have to do with seasons?
This brief but very significant astronomical moments are all due to the earths 23.4o axis tilt. It is because of this tilt that we experience seasonal weather and it’s all to do with the way the suns rays reach the earth surface. In the summer the earth is tilted towards the sun which means that the suns rays have a shorter and more direct path through the atmosphere bringing warmer temperatures. In the winter the earth is tilted away from the sun. This means that the suns rays have a shallower angle when travelling through the atmosphere resulting in a longer path and more scattering meaning that less rays reach the surface resulting in lower temperatures. It is this cyclical rise and fall in temperatures that we know as the seasons and causes the flowers to bloom and animals to migrate. So here’s to the change in seasons and the lengthening of the day, here here!