Tuesday, July 5, 2016

Tonight's Sky for July 5: Earth at Aphelion

For people living in the Northern Hemisphere, it may be hard to believe but, right now, Earth is at a point in its orbit called aphelion, which is a fancy way of saying that it is as far as it will get from the Sun. 

As for how Earth can be its hottest (at least North of the Equator) when it's at its farthest from the Sun, it has nothing to do with distance, but everything to do with geometry.

The Earth's seasons are caused by the planet's 23.5 degree tilt relative to its axis. As Earth goes around the Sun, the angle of a location relative to the incoming solar rays changes. This is the reason why the Sun apparently takes a different path through the sky (high in summer and low in winter resulting in long and short days, respectively) during the year. It is this difference in angle (and resultant day length) that causes the seasons to change.

Oh yes, Earth is roughly 95 million miles from the Sun today rather than the 93 million mile average distance taught in schools.

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