Chaya Shanku

From sticks in the ground to caesium atomic clocks, humans have been keeping track of time with increasing accuracy for millennia. Timekeeping is one of the most important tasks performed by human beings. The history of timekeeping dates back to when ancient civilization observed the sun and moon as they moved across the sky. The current "sexagesimal system" (Base 60) of time measurement dates to approximately 2000 BC from the “Sumerians” (The earliest known civilization in the historical region of southern Mesopotamia, modern day southern Iraq). Many ancient civilizations such as Egyptians, Indian, Mesopotamianc, Greeks, Mayans, Chinese etc measured the time to keep track of the seasons. To measure time, they use various kinds of timekeeping devices like sundials, water clocks, etc.

In ancient India, there were a total 13 numbers of different astronomical instruments used. Already in Vedanga period (around 1000 to 500 BC), the gnomon (stick) was used and it is also mentioned in Kātyāyana sulba-sutra ( Katyayana , 3rd century BC was a Sanskrit grammarian, mathematician and Vedic priest who lived in ancient India. He also composed one of the Sulba Sutras). A very simple and easy method used for measurement of time. Chaya Shanku was the main instrument used at that time in India. The " Chaya Shanku ’’ is a simple device used to find the cardinal direction and Muhurta (time unit used in ancient India). This instrument is also known as “Solar Gnomon”. In Chaya Shanku word, Shanku means a cone and Chaya means a shadow. The simplest version of Gnomon is a stick driven vertically and standing upright, perpendicular to the ground. This stick cast a shadow against the sun on the ground as shown in the above image.

• Working principle of this instrument :

The angle and length of the shadow changes throughout the days as the sun moves through the sky from east to west. By observing these changes in angle and length of the shadow, we can identify the cardinal directions (N, E, S, W) and the muhurta.

• Calculating the Muhurta :

(I already explained what exactly muhurta is. If you want to read it then check out the references no.1).

In simple words, Muhurta is the time measuring unit used in ancient India. According to the standard and modern time measurement, one Muhurta is 48 minutes. There are a total 30 numbers of the muhurta in Ahoratra (a full day, 24 hrs). Out of 30 muhurta, 15 muhurtas occur when the sun is seen in the sky and another 15 muhurtas occur when the sun is not seen in the sky. The length of the stick (Gnomon) was 12 angulas. To calculate the Muhurta, ancient people were measuring the length of the shadow casted by Gnomon (stick). At that time, they used angula as a unit of length.

From ancient times, human body parts have been used as units in the measurements. The small unit is the finger. An Angula is the distance equal to the breadth or thickness of a finger. At sunrise, the length of the shadow of Gnomon is also longest and after sunrise the shadow of Gnomon (stick) falls toward the west. As the Sun moves upwards in the sky, there is a decrease in the length of shadow cast by Gnomon (stick). Suppose the measurement of the length of the shadow is 12 angulas then it means at that time the Muhurta is Maitra Muhurta. The eight Muhurtas from the sunrise to the none are calculated as shown in below:

1) First Muhurta = Raudra = 96 Angulas

2) Second Muhurta = Sevta = 60 Angulas

3) Third Muhurta = Maitra = 12 Angulas

4) Forth Muhurta = Sarbhata = 06 Angulas

5) Fifth Muhurta = Savitra = 05 Angulas

6) Sixth Muhurta = Vairaj = 04 Angulas

7) Seventh Muhurta = Visvasu = 03 Angulas

8) Eighth Muhurta = Abhijita = less than 3 Angulas

# Written by:

• Gaurav Narkhede

• Kunal Sutar

# References:

1) My article on Muhurta:

https://docs.google.com/document/d/1_FPtXVyPYl-V_akwFnIMFjeAtOTE-oYIhc0o_UL20Ec/edit?usp=drivesdk

2) Astronomical Instruments in Classical Siddhantas by Yukio, Ohashi: Research Paper, Indian Journal of History of Science.

3) Measurement of Time by Deepak Joshi, published by Vijnana Bharati, HeadQuarter, Delhi.

4) Standardization of the Time Unit Muhurta Through the Science of Sciatherics in Atharva Vedanga Jyotisha, Sajjan Singh Lishk and S. D. Sharma, Department of Physics, Punjabi University, Patiala.