Now that Christmas and New Year is out of the way its time for another celebration; Happy Perihelion!; OK I’m getting carried away but it’s a good excuse to focus on a really interesting fact that in the Northern hemisphere we experience winter when the Earth is closest to the Sun in it’s elliptical orbit of the Sun.

I have been asked a few times recently by friends why this is so.  The answer lies in the fact that the Earth orbits our star tilted on it’s North-South axis by 23.5 degrees (the 23.5 isn’t that important here only that it is significant enough to make a difference).  When the Earth is at it’s closest point to the Sun, the Southern Hemisphere is tilted towards the Sun and the Northern Hemisphere is tilted away from the Sun.  This means that the Northern Hemisphere inhabitants (me included) experience shorter time spans of exposure to the sun (i.e. shorter days) and being further way from the Sun; all leading to a general reduction in temperature.  The Southern Hemisphere inhabitants are having their summer; lucky so and so’s.

On the 4th July, other than Independence Day (for our US friends), we can celebrate Aphelion where the tables change; Northern Hemisphere people get to sunbath and the Southern Hemisphere people have to rap up warm.

I should add that the main reason for the season change is axel tilt as opposed to the distance from the sun.

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