Monday, December 29, 2014

Tonight's Sky for December 29: The Latest Sunrises

While the solstice (and shortest nights) was last week, the latest sunrises occur now. Why is this? Short answer: celestial mechanics. As for why the Sun doesn't have its extreme rise/set dates on the day of the solstice, it all has to do with solar noon, the point in time wherein the Sun reaches its highest point in the sky, which is the basis for the timing of the solstice. Problem: the Sun doesn't always reach its highest point in the sky as seen from Earth at noon. In contrast, the Sun is at its peak elevation about a week before the solstice in summer, which means that, solar noon being about 8 minutes before Earth noon, that also means that the latest sunrise occurs about 8 minutes earlier, too, thus resulting in the Sun's lowest point at Earth noon being about a week after the solstice.

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