The sundial on abridged armilla 台中簡儀上的日晷

台中簡儀模型上有個日晷，若稍加分析，可確定它是工匠做錯了的。詳情請至http://blog.xuite.net/nycl.chiu/blog/27494787。

There is a gorgeous model of Jien-yi (simplified equiptment, 簡儀, abridged armilla) on display in the National Museum of Natural Science in Taichung, Taiwan. The model was made in China and the original one is still kept in ZiJinShan (紫金山), China. On the  lower level of the model, there a sundial on a horizontal plate. (See Fig. 1). This is not the same thing as what I saw in Beijing's museum where the plate is a ZhengFangAn (正方案, a square table used to find the precise north-south direction) with a long vertical needle seats at its center to cast shadow and then to find the true north direction together with the rings (up to 19 rings) on the its face. Now here on the model the rings were removed and replaced with hour lines of a sundial. The long needle is substituted with a regular gnomon, of course. However, the model maker left four mistakes on this dial: 1. The gnomon were misplaced; the lower tip of gnomon was not at the 'center' of the dial. (See Fig. 2). 2. The hour lines were not split into two groups to form two 'centers' to take care of the thickness of the gnomon. 3. The hour lines for time difference of 12 hours were not aligned. And 4. In between 1 a.m. and 2 a.m., were there only two lines. (See Fig. 3).

The vertical plus vertical azimuth sundial for HuLin middle high school students

中文讀者請至 http://blog.xuite.net/nycl.chiu/blog/23501165

The HuLin middle high school in HsinChu city, Taiwan invited me to give a speech on sundial on the 9th of April. I prepared a compound dial, vertical plus vertical azimuth, model and hand out on which the layout and the instruction were given so that each student could make the same one for themselves after.

The design of the sundial faces is displayed in the following photos. One gnomon plate serves for two dials: the horizontal edge for the vertical azimuth dial and the slope edge for the normal vertical dial. It reads the standard time.

ZhangHua BaGuaShan horizontal sundial

中文讀者請至http://blog.xuite.net/nycl.chiu/blog/22542859

Last winter solstice my wife and I went to ZhangHua BaGuaShan scenery park to see a new horizontal sundial, but failed because the service persons gave us a direction which led us to an analemmatic dial in another park service center in NanTou. After we went home, we realized that the horizontal dial should be in the natural park which is at the entrance to the scenery park, the big Budha statue is just across the street.

The position of the dial is at 120.55ºE, 24.08ºN. The dial was made around the year of 2000, probably designed by 陳乃升and 彭維冠. It is a beautiful one. See Fig. 1. The finger point of the child up high on the seesaw is the nodus. Only three calendar lines were drawn. See Fig. 2. I checked the time it showed and it was accurate. The only thing I can suggest is that if there is an EoT table around it will be much better .

A compound dial: horizontal plus horizontal azimuth

中文讀者請至http://blog.xuite.net/nycl.chiu/blog/22371023
以及 http://blog.xuite.net/nycl.chiu/blog/22374662

In the previous paper, a horizontal azimuth dial was designed without using long vertical needle as shadow casting subject but a slit. In order to read the standard time directly from the dial, EoT analemmas with sharp ends were applied. However, to most people, this is another baffle. There I decided to make another one whose calendar lines go from Jan. 1st to Dec. 31st. See Fig.1.

Then I did the same thing to a horizontal dial and put it with the azimuth dial in a CD box so that no compass is needed. Fig. 2 shows the compound dial is in using.

地平方位日晷 Horizontal Azimuth Sundial (3)

中文讀者請至 http://blog.xuite.net/nycl.chiu/blog/22215751
Typical azimuth dial uses a vertical needle, which seats at the center of calendar circles, to cast shadow on those circles. Those circles are drawn with hour marks so that time can be found from the position of the cross point of needle's shadow and calendar circle of the right date. Once the dial is set in the right N-S direction, nothing is required to move. Just watch the moving of the needle's shadow. (http://blog.xuite.net/nycl.chiu/blog/11134875) This is all right in middle and high latitude zones. In low latitude zone, a problem occurs: the shadow becomes very short at time near noon in the summer since the sun is then near the zenith. That means there is no cross point unless the dial is equipted with very, very long needle, which is unpractical.

A magnetic azimuth dail has no such problem. It uses a long magnetic pointer which crosses over those calendar circles with its supporting needle at their center. When one wants to find the time, he turns the square dial plate until the painted on 12 o'clock line is pointing at the solar azimuth. The hour under the magnetic pointer is the time ought to be.(http://blog.xuite.net/nycl.chiu/blog/11134815) The diameters of calendar circles for summer time can be made greater to hold reasonable hour resolution without worrying the problem as in the former case because there is no shadow casting needle. So a magnetic azimuth dail is a suitable one in low latitude zone.

Now a days a long magnetic pointer is hard to find in stores. An alternative is represented here for Hsinchu, Taiwan, which is at 24.9N and 120.9E. Fig. 1 shows the parts and tools needed. The hour diagram is a little bit complicate for it intends to give the standard time. Fig. 2 shows the finished dial. To find the time, one sets the black thread in S-N direction first. Then he flips up the slit and turns the dial plate (CD) until the sunshine passing through the slit is right on the azimuth line, as shown in Fig. 3.

Now the hour on the right calendar circle under the black thread is the time he is looking for. For example, as in Fig. 4, if the date is the 19th of Feb., the time is 1:10; if the date is the 21st of June, the time is 12:00.

新竹市清華大學新日晷 New Sundial on NTHU campus, Taiwan

這日晷在新竹市清華大學校園內，2006年為慶祝清大在台復校50週年而建。 其獨特之處有三： 1. 面盤，就是那藍白色像水又像天空的大圓面，向北傾斜5.2度。 2. 投影體的南、北兩端都開有小孔，夜裡從南孔向北孔望去，可見北極星。 3. 面盤上的日期線，除了夏至、春分、秋分和冬至外還有清大校慶日和雙十國慶日。
在面盤東北方地面上有兩塊銅牌，一塊說明建造原委，另一塊是時差修正表。
This sundial was given to the Nat'l Tsing Hua University in April, 2006 as a gift to celebrate its 50th anniversary of re-erecting at Hsinchu. The mosaic dial face, 8m in diameter, is tilted 5.2 degrees down north. The highest point of the gnomon is about 185 cm from the face, which is decorated in blue and white to imply water and sky. The gnomon's east-west width is 30 cm. Near the top edge of north end is there a hole. A smaller hole is found at south end. Through these two holes, one may see the North star in the night. Five calendar lines are given; summer and winter solstices, equinoxes, the National Day (Oct. 10th) and the University anniversary (Apr. 29).
There are two bronze plates on the ground north-east to the dial face. One states why and how this sundial was built, the other gives an 'equation of time' table on a basis of every minute of change. The picture above shows only the latter.
This sundial was designed by Professor Emeritus Chi-Lian Chiu (chemist) and Mr. PoJui Lin (artist).

單純垂直方位日晷 Simple Vertical azimuth sundial

中文讀者請至http://blog.xuite.net/nycl.chiu/blog/22000225

In low latitude zone area, horizontal azimuth sundial is not a good choice if one likes to make and use a sundial because its time resolution is very low during summer time. A simple vertical azimuth sundial,on the contrary, is much better. A model for 24.79 N (NTHU, Hsinchu, Taiwan) is made.

Fig. 1 gives the south side and Fig. 2 shows the north side. To use it, one should draw a true west-east line, put it on the line and then hold it vertical. If a horizontal surface is more convenient for him to find, then a supporting bottom can be made as shown in figures.