Last week I hosted my company’s annual international distributor meeting. One of my Korean guests was kind enough to bring me a small gift, something I had never seen before, a pocket sundial modeled on an ancient Korean sundial called Angbu Il-gu (“cauldron-like sundial”). According to this (what else?) Wikipedia article, the original version of this sundial was invented by Jang Yeong-sil and other Korean scientists sometime in the 1400’s during the early Joseon Dynasty.The picture at the bottom of this article shows what the much larger original looked like (museum photo from Wikipedia Commons, courtesy Bernat).
The pocket sundial fortunately included some English notes, explaining that the 13 lines that are roughly perpendicular to the pointer are seasonal lines. The far right line is the winter solstice (lowest sun, longest shadows) while the leftmost line (aligned with the tip of the pointer in my photo) represents the summer solstice. Today is just about two months past the winter solstice, and the shadow’s tip touches the second line. The lines that are roughly parallel to the pointer are time lines (half-hour increments), with the longest (center) line representing noon. This picture was take at 12:36 EST, and the shadow is well short of the 12:30 line, but the instructions also mention that some adjustment is needed for longitude, though the English explanation of this isn’t very comprehensible. They also didn’t mention the use of the compass, but I knew enough to align the red end of the compass needle with north.
I was surprised to get such a cool little gift, although I think my Korean friend knows that I have an interest in astronomy (or at least optics). I was also surprised that it is sunny enough today to test it!
(looks like this was taken right around the same month and time of day as my photo)