Daily Archives: September 16, 2008

The image of the Sun

Today at Moses Lake the sun went down in cloudless skies. Naturally, my mind drifted to the subjects of religion, time, astronomy, sunspots, optics, history, and climate, and of I ran into the fermentation section of our ethanol plant to see if I could image the sun. The west wall of our plant has a lot of little (maybe 1/8″ = 3mm) holes in it and a good view of the setting sun. The sun shines through each of these holes, and they produce images of the sun on the opposite wall. These are, literally, sunspots in the sense of “spots of sun”:

Images of the sun like these were used by the Catholic Church as a very accurate sun dial. They drew curves on the floor to indicate noon, summer and winter solstice, etc. These are called Meridian lines. When one specifies a time as “AM” or “PM”, this is an abbreviation for “ante meridian” or “post meridian.” The moment at which the disk is perfectly centered on the meridian curve indicates high noon. High noon occurs in slightly different directions depending on the time of year, so the meridian figures are curved in a distorted figure eight, called an analemma. The very interesting history of the meridian lines inside churches is the subject of the book The Sun in the Church: Cathedrals as Solar Observatories by J. L. Heilbron.

With the improvement of time keeping, the necessity of making solar observations by sunshaft decreased and some of the beautiful meridian curves have been removed from cathedral floors. The Catholic Church, however, still supports astronomy. The tradition is carried on at the Vatican Observatory in Arizona.

You can get a better sun image at home if you use a piece of paper. After adjusting contrast and brightness, here’s my image of the sun:

The above is a nice clean image of the sun. You can tell that it is in pretty good focus by noticing how sharp the border of the sun’s disk is. If there were sunspots visible at that time, I would have seen them.
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Filed under History, physics