Last Sunday, I didn’t hike because of a knee injury. I remembered that at noon the Eugene Astronomical Society sponsored a weekly solar viewing in Alton Baker Park, appropriately near the 1:1 billion scale model of the Sun, part of the solar system which runs for 2 1/2 miles west along the Willamette River. I lead a New Years’ Eve Day walk through the solar system for the hiking club and know it well. I decided to go over and see what it was all about.
I do my solar viewing during eclipses, so viewing the “normal” Sun is strange for me. When I arrived, three members had telescopes set up, two with Hydrogen Alpha filters and a Dobsonian with a nice solar filter. A Hydrogen Alpha filter removes all light except the wave length emitted caused by an electron’s jumping from one specific orbit to another. They allow prominences on the edge of the Sun to be seen well, and I saw one such prominence far larger than the Earth.
After my look, I settled on the cool grass to look for Venus in daytime, more difficult to do here in Oregon, at lower elevation, more humidity, and in summer more smoke. I never did find it. Jerry, who is the EAS’s spokesman, runs the show. He has written 15 science fiction books and remarkably well-versed in all areas of astronomy. He recognized me by name when I showed up, speaking volumes to his skills at facial recognition as well, since after the eclipse a year ago, we have seen each other twice. After chiding myself for my laziness, I finally went to the last monthly meeting.
Somewhere in all of this, we started talking about sundials.
Jerry brought the shell of one that had been thrown out, where the shadow caster, or gnomon, was put on wrong and had the wrong latitude as well. He was interested in bringing the dial back to life, so we started chatting about various dials. I have built several horizontal and vertical ones, plus a 20-footer on a concrete slab, an analemmatic, in Sonoita, Arizona, where one could stand on the date with the shadow’s reading the time. I’m not much of a builder, but math is integral to making a sundial, and I like math.
I was able to help Jerry when I reminded him of a correction we need to make is where we are in the time zone, in addition to the correction of our watches to exact time. We are a bit more than 123 degrees west longitude, and our clocks, plus daylight savings time, are set for local noon at 1 p.m. at 120 degrees west, 8 time zones (a time zone is 15 degrees latitude) from Greenwich. The extra 3 degrees and change delays local noon by 12 minutes and 46 seconds, so Sun’s culmination, or furthest south, is after 1 o’clock. There is yet a third correction that must be made for the “Equation of time,” which takes into account the difference of “Sun time” to clock time.
These two ways of measuring time are slightly different: clock time is 86,400 seconds per day, where each second is “the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.”
Got that?
The Earth’s orbit marking the day’s length—measured from noon to noon—is not quite 86,400 seconds or a bit more. If the Sun is running “fast,” which it does especially in September and October, we note an earlier sunset, which is why October evenings (at least in the Northern Hemisphere) become so dark so soon. The mornings don’t change much, because while the Sun is moving south, delaying sunrise, the Sun runs “fast,” speeding up sunrise, and the two effects tend to cancel each other.
When the Sun is running “slow,” especially in January and February, it is slow to rise, giving rise to the dark mornings of January. The slowness works the same way in setting, however, which is why by New Years’ Day most people know that the Sun is setting later than it did at the beginning of the month.
It is not a good reflection on me that I tried to convey all of the above information in words during a time when nobody was viewing through the telescopes. I left out the making of an analemma, the path the Sun takes through the sky at the same clock time, during the year. It is the odd-shaped Figure of 8 on the globe. If one can understand what the analemma means, one is well on the way to understanding the rhythms of the Sun and the changes in sunrise and sunset times. I’ve made analemmas, and it is a great project for elementary school students, for it teaches how the Sun takes the same path across the sky in fall and spring but doesn’t rise and set at the same time.
Probably a better lesson is that an analemma takes a year to make, and one can’t speed up the process. All is needed is an object that casts a decent shadow on the ground and the ability to mark the shadow periodically over a year, which helps develop delayed gratification skills.
I’ve made sundials to keep track of time of meetings I’ve attended, throwing people a little off balance, setting a different tone for the meeting. I’ve made many noon marks, too, where the Sun is highest in the sky for a given day, demarcating the change from morning to afternoon. These were part of the pioneer homes in our history, and some still have them today. Noon marks are along a straight line, but they occur at different clock times.
With fast and slow Suns, hydrogen Alpha filters, and Dobsonian telescopes, I again re-learned one of life’s lessons: when one does something new, out of the ordinary, one may predict what will happen, but one will likely have a very different experience than what was predicted. I went over to look at the Sun and to support the local society. I didn’t expect anything special.
Instead, I found my knowledge of an area of the Sun useful, connected with a couple of people and made a difference by my presence. That’s not a bad way to spend time, whether Sun time or clock time.
Tags: Outdoor writing
Boreal B[l]og 
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