Paying attention in class

Wednesday, December 18, 2013

OK, first off, all of you get a D- for not noticing that I called Aldebaran a planet and not a star in last week's astronomy lesson. Or, some of you may have noticed and sent an email which I haven't seen yet because I have been out of Internet contact for the last week in the wilds of Nebraska.

See, it pays to pay attention in class.

Seriously though, if anyone has a question or comments please send me an e-mail at and I will be happy to help. In fact, after the start of the year I will be delving into the "old mail bag" once again.

In case you haven't noticed, winter is coming, or for some of us it is already here. With the sub-zero temperatures of last week it certainly seemed like it. However, we all know that the start of any season is not a function of the weather; it is a function of astronomy.

Winter officially starts when the Sun reaches the furthest point south in its travel across the sky, in this case, the Tropic of Capricorn at 23.5 degrees south of the equator. That distance just happens to be the same as Earth's axial tilt.

Conversely, the furthest point north is the Tropic of Cancer at 23.5 degrees north of the equator which will mark the beginning of summer for the northern hemisphere.

For us in the northern hemisphere that event will be on Saturday, Dec. 21, at 10:11 am MST. For our friends in southern climbs, it will be the start of summer. That is why I always enjoy seeing photographs in the newspaper of people in Australia celebrating Christmas Day with a trip to the beach.

The event is called the "Winter Solstice" because the Sun seems to stand still for a few days in relation to the horizon in its rising and setting. Solstice is Latin for "Sun stands still." It also is supposedly the longest night and shortest day of the year. However, that particular event depends on where you live.

For instance, we good folk here on the Golden Plains of southwest Nebraska will have our longest night and shortest day during the week of Dec. 19 through Dec. 24. when the length of day will be nine hours and twenty minutes for each day.

SKY WATCH: Full moon yesterday, Tuesday, Dec. 17. Third quarter moon is on Wednesday, Dec. 25. Bright Venus is still the "Evening Star" in the west after sunset and will be setting about two hours after local sunset. However, the sky will not be bereft on any bright object. Almost as bright Jupiter will be rising in the east as Venus is setting in the west.

Jupiter will be at opposition--opposite the sun in the sky--in early January and will grace our evening skies until June. It is currently in the constellation Gemini, the Twins, and the two bright stars to its left are Castor and Pollux, Castor being the one on top. Since Jupiter takes 12-years to orbit the Sun, it generally stays in or near each zodiacal constellation for a year since the zodiac follows the ecliptic as do the planets and the moon.

If you will be outside looking at Venus about an hour after sunset, look a little further to the left--toward the south--for our old friend Fomalhaut, the brightest star (and the only star you can see) in the constellation Piscis Austrinus, the Southern Fish. Fomalhaut is called the "loneliest star" because there are no other bright stars in that area of the sky. All the stars of its constellation are fourth magnitude or dimmer and thus difficult to see.

NEXT WEEK: The true meaning of Christmas, and more astronomical blathering.

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