Solar noon marked over the course of a year. The figure-eight pattern is called an Analemma
Believe me, if you grew up in Texas, where summer heat tops the century mark for weeks on end and even the morning lows offer little relief, you’d feel December was pretty damn magical. This month dawn and dusk stretch out, as the sun marches steadily to the Winter Solstice. The solstice was a magical time for our ancient ancestors, too, the sun looked like it was going away and they were afraid it might keep going! So after the shortest day of the year, anywhere from Dec 20 to 23 on our calendar, a returning sun was cause for celebration indeed. You might think the shortest day of the year would have the latest sunrise and earliest sunset. But here in Texas and throughout the temperate section of the northern hemisphere, it actually doesn’t work out that way.
Here in North America, if you mark the highest point the sun reaches in the sky each day, called Solar Noon, and put them all together, it makes a slumped-over squashed figure-eight like the one above called an Analemma. If you look at the bottom, the Winter Solstice happens at the inflection point marked 21.12. But thanks to the earth’s axial tilt and other factors, solar noon happens a little later each day as Winter approaches, and that means the earliest sunset has already happened before the solstice is reached. If you looked at the image you can somewhat visualize this, when the sun is just above the Solstice it sets a little earlier and when it’s just below the Solstice point it rises a bit later. The earliest sunset is happening this whole week in Texas and the latest sunrises will occur on January 10 and 11, 2012.
The shortest day happens in between those two times, and that of course of the Winter Solstice itself which is scheduled for 5:30AM UTC on Thursday, Dec 21. Unless of course the sun really decides this time not to return and just keeps on going …
The (Re)Birth of the Sun, right?
AJ
No, no, no … That’s NEXT year!
It’s actually been dropping into the high twenties at night this week. Crazy.
I like Texas winters. Minimal or no snow, some icing, and gorgeous sunrises and sunsets.
Depends on where you are in Texas, Rawnaeris.
Born and bred there, I’ve lived in several parts. What you describe is prevalent in Central Texas, hill country. Go north a few hours, and you get a LOT of ice at times.
Go south to the Gulf Coast, and you rarely even see frozen water.
Plus, the further west you go from the Louisiana border, you lose 10 inches of rainfall for every 70 miles you move, but the Panhandle gets a lot of snow sometimes.
It is a picture of contrasts. If you don’t like the weather, either move west or wait five minutes!
According to the linked Wikipedia article, the analemma is created by recording the sun’s position at clock noon, not solar noon. Since the duration of a solar day varies based on the position of the Earth in its orbit around the sun, solar noon does not occur at clock noon.
Is Wikipedia incorrect, or is this post incorrect?
Analemmas are produced by using the same time, solar noon works well because it’s apples to apples, but if we removed daylight savings, the difference between the two would probably not be visible without precise gear that can measure arc minutes, thus it makes the same pattern regardless if you use solar or clock noon, or even if you mix the two up, again provided daylight savings is removed. It would make the same pattern if you used the half way point between highest posiiton of the day and sunrise, or the halfway point between sunset and the high points, etc. Make sense?
RW Ahrens, you caught me. I’m from the southern side of North Texas on the edge of Hill Country.
Recently moved a few hours closer to Oklahoma, so we’ll see how that goes, weatherwise.
I am puzzled by your description.
You describe plotting the position of the sun at solar noon, when it is at its highest. But I was under the impression that the sun reached its highest point when it was due south (for you, for me it’s due north). So for each point on your plot the sun should be in the same direction.
How do you get the left and right movement in your diagram?
Solar noon won’t work, as that is the time of day when the sun is due south. The analemma is caused by the deviation of our 24-h mean solar time and the true position of the sun. Part of the year the sun runs ahead of our clock, and part of the year our clocks are running ahead of the sun. The maximum deviation is on the order of a quarter of an hour either side, so you end up with the sun “moving” 7.5 degrees or 15 times its diameter in the horizontal, if observed at the same (clock) time every day.
The image you show, btw, is definitely not taken at noon. ‘O’ is German for ‘east’, so this image must have been calculated for early morning sun.
I asked some photographers freinds and they said is indeed solar noon, the highest point the sun reaches each day, that is the easiest time to create such a figure. But you can make the same or a very similar pattern if you use the same time everyday, as long as you remove daylight savings and as long as the sun is above the horizon even on the shortest day. They suggested most images are done to show the horizon for artistic reasons. The image above is actually not done with live shots of the sun. It was calculated and shopped to illustrate the effect.
It’s actually been dropping into the high twenties at night this week. Crazy.
I like Texas winters. Minimal or no snow, some icing, and gorgeous sunrises and sunsets.
The only time I can stand living in San Antonio, temperature wise, is from November to February. The rest of the year it’s too damned hot. I’m trying to talk the husband into moving north. I really like the cold, as long as I have a garage so I don’t need an engine heater. Snow isn’t all that great after the first one of the year, blizzards are a drag, but I can live with those to be comfortable again, and have seasons again.
I like San Antonio, but the weather most of the year is the pits.
Aquaria,
I’m going to be in San Antonio for the New Year. I’ve heard the celebration on the Riverwalk is quite amazing.