December’s Radiant Sun And The Zodiac’s 13th Sign

The sun is already low in the southwestern sky at 4 in the afternoon in early December. Photo: Bob King

I am a lover of December’s radiant sun. When the weather’s fair, it’s always in my face. Sunlight is there in the morning when I open the shade, poking from between trees during a walk and beaming between downtown buildings into the alley behind the parking garage at work. I face it squarely with a smile and everything else is silhouette.

It’s no wonder the sun’s in our face from late fall to late winter. For those living at mid-northern latitudes it never gets very high above the horizon at this time of year. Here in Duluth, Minn. the sun peaks at just 21 degrees at noon today – that’s only two fists held at arm’s length. You can’t help but face its brilliance.

We all know that winter’s low sun means late sunrises and early sunsets, adding up to short days and long nights. Starting today through December 13th we experience a sequence of earliest sunsets of the year from the northern hemisphere. That’s 10 consecutive days when sunset times barely budge, changing less than a minute during the span. Then, grudgingly at first, the trend reverses and the sun begins setting later starting on the 19th. I should point out there is some variation on these dates depending on your latitude.

The Earth's speed varies with distance from the sun during the the course of the year. Illustration: Bob King

On the contrary, the latest sunrises begin more than a week after the winter solstice on December 29 and continue through January 8. By the 9th, sunrise and sunset times work together to rapidly lengthen the days and shorten the nights.

The reason they’re out of sync with one another has to do with the tilt of the Earth’s axis combined with its elliptical orbit. If our planet orbited in a perfect circle, its orbital speed would be constant, but in an elliptical orbit, we’re closer to the sun on one side of the ellipse that the other depending on the time of year. And since speed varies with distance from the sun, Earth’s velocity around its orbit is constantly changing. When closest at perihelion in early January, Earth moves faster than when farthest in early July at aphelion.

The whole business is a bit complicated but suffice to say that the sun continues to drop lower in the sky until after the solstice resulting in later sunrises. At the same time, Earth’s orbital speed increases as we approach January’s perihelion causing the sun to move more quickly toward sunset. For a complete explanation, I refer you to Prof. Kirk Korista’s illuminating piece Sunrise, Sunset and the Solstice.

The sun, shown at noon, travels through southern Ophiuchus between Nov. 30 and Dec. 18 before moving into the traditional zodiac constellation Sagittarius (abbreviated as Sgr). Ophiuchus' border is shown in red. Created with Chris Marriott's SkyMap

As you suck in those solar rays and stand amazed at the brevity of daylight, you might be interested to know the sun took leave of the official zodiac constellations on November 30. Yes, that’s right. Never mind Virgo, Libra, Scorpius and their ilk – the sun is spending its days in Ophiuchus the Serpent Holder. A little fluke of mapping convention makes Ophiuchus the unofficial 13th constellation of the zodiac. Traditionally, constellations were known for the patterns their stars formed, but in 1930 the International Astronomical Union felt it was important to standardize constellation boundaries. Among other reasons, it was done because variable stars – stars whose light output changes with time – are named after the constellation in which they’re located. Without a boundary, astronomers could end up giving different names to the same star, creating confusion.

So we got boundaries. When they were drawn up, Ophiuchus (oh-fee-YOU-kuss) received a chunk of real estate almost down to the bright star Antares in Scorpius. The sun passes through this region between November 30 and December 18 during its yearly swing through the sky. If you were born on or between those dates you’re officially unofficially an ‘Ophiuchus’, what some might consider the 13th sign of the zodiac.

And what would be the traits of an Ophichus personality? Let me provide some guidance. I predict you’ll fall in love, celebrate with friends, act on impulse, find happiness in solitude, get to know a Pisces, be involved in a difficult relationship, be taken advantage of and spend lots of time focusing on priorities. Any Ophichusses out there? Am I close?

9 Responses

    1. astrobob

      Hi Michael,
      Unless it miraculously survives long after perihelion it won’t be visible from mid-northern latitudes like yours and mine. Your best chance to see will be online at the SOHO site as described in the blog. I’ll have an update soon.

  1. RC

    I loved the Ophichus personality traits, thanks for the laugh!

    Also, thanks for the link explaining the discrepency between sunrise and sunset times. I’ve always wondered about that.

        1. astrobob

          Great page Carol. Thank you. One of my astronomical goals is to condense this explanation – and others like it – into two or three sentences. A great challenge but I will not give up!

          1. caralex

            Yes, it’s a huge challenge, and one of the most interesting phenomena I’ve ever tried to explain. I’ve usually been met with blank stares when I’ve tried! I once found an excellent page showing the sun making its way round the analemma, which made it crystal clear for me, anyhow, why the latest sunrise was on 4-5 January for my latitude. If I ever find it again, I’ll forward it to you.

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