Happy Solstice!

The Beginning of a New Year

Well, the world hasn’t ended, although I hear a lot of people are still writing “Baktun-13″ on their checks. But, you’ll be happy to know that our planet didn’t get hit by a rogue planet, or get eaten by space dinosaurs, or get blasted with a cosmic beam from the center of the galaxy, or any of the other threats that were getting tossed around the Web for the past few years as predictions of what would happen when the old Maya calendar flipped over from the end of one Long Count to the beginning of a new one. So, today (for Maya people) is 13.0.0.0.o — which kind of looks like a computer IP address. Well-played Maya!  Well-played!

What Earth’s solstices and equinoxes look like from space. Courtesy NASA.

However, another useful thing to know is that today is the December solstice. It’s the day when the Sun reaches its most southerly declination (position in the sky) throughout the year.  For folks in the northern hemisphere, it’s the first day of winter. People in the southern hemisphere are celebrating summer!

From here on, the Sun will appear slightly higher in the sky each day until it reaches its most northerly point on June 21, 2013.  This apparent “motion” of the Sun north and south is actually something you can measure throughout the year.  Find a convenient place on the horizon and watch where the Sun sets or rises. Note that point and do the same thing each day (or every few days).  You’ll notice that the Sun does traverse the horizon throughout the year.  Why does this happen?

The answer: because Earth is tilted on its axis. It’s tipped over by 23.5 degrees from the plane of its orbit around the Sun. During some parts of its orbit, Earth’s north pole is pointed toward the Sun and then the Sun appears farther north. For northern hemisphere folk, this is when we get spring and summer, and southern hemisphere people experience fall and winter. During other parts, the north pole is ponting away, and then it appears farther south in the sky.  In the north we have fall and winter, and in the south, we have summer and spring.  The sunrise and sunset positions for all of us change throughout the year depending on where the north pole is pointing.

So, the solstice is really just a “stopping” point in the apparent position of the Sun against the horizon. From here on out, it will look like it’s slowly moving north. And, that’s a great reason to celebrate the “new year” that starts with the December solstice. Yes, it’s different from the calendar year change. But, calendars are culturally based constructs that help us tell time and seasons. The motion of Earth around the Sun is what all these calendars are based on  (plus some other interesting things like the orbit of Venus and the phases of the Moon).

Enjoy your solstice, folks!

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