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6.8 Jantar Mantar of Rājā Jai Singh Sawai

Mar 22, 2025

Ancient Indian Astronomical Instruments

Introduction

  • Ancient Indians developed numerous astronomical instruments.
  • These instruments were crucial for estimating key numbers and positional accuracy of celestial bodies.

Instruments Overview

Shanku (Vertical Stick)

  • A simple vertical stick, known as Naman in astronomy.
  • Purpose: Setting the cardinal directions (East, West, etc.).
  • Method:
    • Place Naman vertically on level ground, pointing to Zenith.
    • Draw a circle with Naman's base as the center.
    • Mark points W' and E' where the shadow tip hits the circle in the forenoon and afternoon.
    • These points help determine the east-west direction.

Large Wooden Circular Disk

  • Description: A disk divided into 60 ghaticas and 12 zodiac signs (Aries, Taurus, etc.).
  • Purpose: Determine the movement and position of the sun (Lagna).
  • Function:
    • Rotate around the axis so shadow falls on sun's position at sunrise.
    • The number of ghaticas between sunrise and shadow position indicates Lagna.

Chakra Yantra

  • Description: Plate made of metal or seasoned wood with a central needle.
  • Purpose: Measure the angular height of the sun.
  • Historical Context:
    • Used in observatories by Raja Sawai Jai Singh in Jaipur and Varanasi.
    • Large instruments mounted on pillars, aligned with Earth's axis.

Contribution of Raja Sawai Jai Singh

  • Lived between 1686 and 1743 CE in Jaipur.
  • Built the Jantar Mantar, a significant milestone in Indian astronomy.
  • Reason:
    • European instruments were error-prone and weather-affected.
    • Built large, sturdy instruments to ensure accurate observations.
  • Jantar Mantar Locations: Delhi, Jaipur, Varanasi, Ujjain, and Mathura.

Legacy of Indian Astronomy

  • Key Points:
    • Long tradition with Vedic references.
    • Concepts of month/year adjustments between lunar and solar calendars.
    • Development of formal mathematics for astronomy during Aryabhata and Siddhanta periods.
    • Contributions by Nilakantha Somayaji and others.
    • Panchanga: Indian astronomical calendar based on scientific principles.

Conclusion

  • Indian astronomy boasts a rich legacy with robust scientific foundations and innovative instruments.

These notes provide a summary of the development and significance of ancient Indian astronomical instruments, focusing on the innovation and contributions of historical figures like Raja Sawai Jai Singh.

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