Wednesday, January 4, 2012

Perihelion Versus Solstice

For some reason I always thought Perihelion would occur the same time as Winter Solstice...

But it doesn't.  Perihelion is the once a year event (0100 GMT 5 January 2011 this time around) when the Earth's passes closest to the sun on our slightly elliptical orbit . Yes, we are five million kilometers closer to the sun in Winter than we are in the Summer.  Winter solstice is when the apparent path of the sun reaches it lowest point in the sky due to our planet's 23-1/2 degree tilt.  The axial tilt results in sunlight hitting the northern hemisphere at an angle, resulting in much less energy absorption, then Winter happens.  Aphelion occurs - also only coincidentally - close to but not on the summer solstice.  If you have the correct instruments and the proper safety filters the sun appears ever so slightly smaller, 1.67% smaller to be precise.  And, the farther we are from the sun the slower we move along our eccentric orbital path, which is why Summer is actually a couple days longer than Winter.  Go figure.  There's a lot going on up there, whether we pause to think about it or not...

Photo credit: APOD

No comments:

Post a Comment