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#BAFact: The standard calendar year is the time it takes to go from equinox to equinox: one tropical year.

You might think the length of the year is an easy thing to understand, but in fact there are lots of different "years": sidereal, anomalistic, and so on. We use the tropical year - about 365.24 days long - to account for the change in the seasons as the Earth's axis slowly wobbles over 26,000 years. It's actually pretty cool how this comes about, and I have a page with all the excruciating details:

http://blogs.discovermagazine.com/badastronomy/2012/01/01/another-orbit-why-you-dont-look-a-rotation-older-than-4-56-billion-years/
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Queen Janai's profile photoWilliam Andy Smith's profile photoDouglas Blaack's profile photo
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I've had the term "sidereal day" banging around in my head for decades, but never understood what it meant until now.  Thank you!
 
Ow! Sprained my brain... all part of learning something new, right? :D
 
I always thought the tropical year should start on winter solstice. Jan 1 seems so arbitrary.
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