Monday, September 19, 2011

Sunny paradoxes – part 1

A sunset over Cumberland Sound
The sun continuously shines on Earth, but how much sunlight reaches us varies through the year. Since the Earth's orbit is elliptical, we are closest to the sun around 3 January and farthest around 4 July. Every illustration of the elliptical orbit of Earth that I've seen shows a hugely skewed orbit, which could lead one to think Earth would have its hottest global temperature in January.

However, the elipticalness of our orbit doesn't have much of an impact. From Wikipedia: Earth's farthest point is 152,098,232 km and the closest 147,098,290 km – a difference of 4,999,942 km, which is a small fraction of the orbit's radius (yeah, it's still a huge number, but everything in space is huge). Another way to look at this is to consider the eccentricity of Earth's orbit. Eccentricity is a measure of how circular an orbit is, zero is a perfect circle and one isn't a closed orbit (like a slingshot). Earth's eccentricity is about 0.02 – really close to a circle.

For those of us in the northern hemisphere, we are closest to the sun in the middle of winter – not the hottest time of year. Instead, it's the Earth's tilt that creates the seasons – we are tipped 23.5 degrees from the plane of Earth's orbit. When the pole closest to us is tipped away from the sun, we get winter. At the pole itself there is complete darkness (good for vampires).

The tilt of the Earth's rotation plays a greater role in our temperatures than the elipticalness of Earth's orbit. Either way, we still get a free trip of 150 million kilometres each year.

No comments:

Post a Comment