A Tale of Two Timekeeping Sticks

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Once upon a time, there were two sticks. One always stood straight and the other one bowed. And their shadows told some interesting information about ... TIME! So, we decided to compare their shadows on the day of the Equinox.  

The last time (check the previous post), we tracked the shadows using a simple Sundial where a stick (pencil) is fixed in the vertical upright position. Though the shadows were moving in the clockwise direction (fortunately ), the hourly gaps were not equidistant. So, tracking time seemed quite difficult! For this second observation, we prepared a horizontal sundial to compare the findings with our earlier sundial. (The making of this horizontal sundial is based on https://www.sundials.co.uk/projects) Though it is not as simple as fixing a vertical stick, it is not very difficult either. To keep the project simple, we used thermocol sheet for the base and the triangle, and a stick as gnomon. The stick (gnomon) should be parallel to the Earth’s axis. To achieve this, we fixed this on a triangle as shown in the picture below. The angle at the base of the stick should be the same as the latitude of the place where the sundial is to be kept.


The next task to draw the hour lines. For this purpose, we need to first draw a semicircle and then divide it into 12 parts. This can be done with the help of a protractor and marking the points at 15 degrees distance. Now, extend the lines and fix the paper with the tilted stick as shown. The other side of the paper should touch the base of the triangle. 


Mark the points where the lines are touching the base. And then from the marked points, draw the lines upto the base of the stick. Extend the lines on the opposite side as well. Your end product should be something like this.


In order to fix this sundial in the garden, you will require a compass. We fixed the sundial such that the stick points North (since we are in the Northern Hemisphere). As you can see the horizontal sundial is showing the time as 10 o’clock, whereas the clock time was 10.50 AM. Is something wrong? Well, the difference arises due to two things. First reason is quite obvious. Our clock shows the standard time for India, whereas the sundial shows the actual local time. Secondly, the time gap between the successive noon is not exactly 24 hours throughout the year! And the clock time averages these daily differences.


Then we got the successive readings as follows:

 


 

11.50 AM (Too many clouds at 12 noon, so could not get the picture)

12.48 PM (Showing the solar noon)

 

 

3.00 PM (with close-up of the horizontal sundial as the shadow was not visible properly)

5.00 PM 

So, here are the observations:

1. The time shown by the vertical stick matched during the middle hours but not in the evening.

2. The time recorded by the horizontal sundial showed remarkable consistency and lagged behind the clock time by approximately same amount of time throughout the day. 

The horizontal sundial is promising, though we need to make further observations to make sure that the horizontal sundial works with same level of efficiency throughout the year. So, we will continue with our little experiment the next month! 😀😀




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