Astronomy in India

Astronomy in India

Astronomy, the scientific study of celestial objects, their positions, motions, radiations, and nature, is one of the oldest sciences known to humanity. Its origins can be traced back to the earliest times when humans began living in the open and observed the sky with wonder and curiosity. Early humans noticed recurring celestial phenomena such as the phases of the moon, eclipses, and the appearance of various stars and constellations. Without scientific knowledge, these phenomena were often woven into myths and religious beliefs, reflecting humanity's attempt to understand the cosmos. India, as one of the world's oldest civilizations, has a rich and ancient tradition of astronomy. The Vedas and other religious texts contain philosophical speculations on cosmology and the origin of the universe. Alongside these philosophical inquiries, practical astronomy flourished as it was essential for daily life. For example, predicting the arrival of rains was crucial for agriculture, and determining auspicious times for ceremonies like marriages and festivals depended on celestial observations. Eclipses, comets, and shooting stars were often seen as omens affecting rulers and society, prompting kings to appoint astronomers to monitor the skies and report significant events. Astrology, the belief that celestial motions influence human destiny, was widely accepted, making the tracking of heavenly bodies a matter of social and political importance. Ancient Indian astronomers focused on several key tasks: devising calendars and time-keeping devices, predicting the timing and duration of astronomical events such as eclipses, noting the appearance of particular stars, and observing the sun, moon, and planets. Achieving these goals required accurate measurements of celestial distances and complex mathematical calculations. Indian astronomers made significant contributions in these areas, though Western historians have sometimes overlooked their achievements. This section sets the stage for understanding the development of Indian astronomy, including the Indian calendar, eclipses, solar movements, and the contributions of notable Indian astronomers and observatories.

• Astronomy studies celestial objects, their motions, and radiations.
• Ancient humans observed celestial phenomena and incorporated them into myths.
• India has a long tradition of astronomy dating back to the Vedic period.
• Practical astronomy was essential for agriculture, festivals, and astrology.
• Kings appointed astronomers to monitor celestial events like eclipses.
• Indian astronomers developed calendars, predicted eclipses, and observed stars and planets.
• 📌 Astronomy: The scientific study of celestial objects and phenomena.
• 📌 Celestial bodies: Natural objects visible in the sky such as stars, planets, the sun, and the moon.
• 📌 Eclipse: The darkening of one celestial body by another.

Astronomical Practices in India

The Indian calendar, often called the Hindu calendar, is a lunisolar calendar that integrates both lunar and solar cycles. Unlike purely lunar or solar calendars, the Hindu calendar uses the lunar month to fix dates of festivals and auspicious days, while the solar month regulates daily life activities. The lunar month is based on the moon's orbit around the Earth. The sidereal period of the moon (relative to stars) is 27.3 days, while the synodic period (relative to the sun, as observed from Earth) is 29.5 days. The lunar month is divided into two halves of approximately 15 days each: the dark half (Kṛṣṇapakṣa), starting with the full moon as day one (ekam), and the bright half (Śuklapakṣa), starting with the new moon as day one. Different regions in India have varying practices regarding whether the month starts on the new moon or full moon day. Solar months are defined by the sun's apparent motion through the zodiacal constellations (Rāśis). The ecliptic is the path of the Earth around the sun, and a belt of about 8 degrees on either side of the ecliptic is called the Zodiac or Rāśi Cakra, containing 12 constellations. The sun takes about one month to pass through each Rāśi. The day the sun enters a new Rāśi is called Saṅkrānti; for example, Makarā Saṅkrānti is when the sun enters Capricorn (Makarā Rāśi). The solar month length varies between 29 and 32 days due to the unequal sizes of constellations and the sun's non-uniform orbital speed. Nakṣatras are prominent stars or star groups used to track the moon's position. There are 27 or 28 Nakṣatras, each associated with a day of the lunar orbit. The lunar month is named after the Nakṣatra seen on the full moon day. Because a lunar year is about 11 days shorter than a solar year, the Hindu calendar reconciles this difference by adding an extra lunar month (adhikamāsa) approximately every three years. This adjustment keeps festivals aligned with the seasons. The rules for adding this extra month are complex but ensure that lunar and solar years remain synchronized. Tithi, or lunar date, is another important concept. It is defined by the angular separation between the sun and the moon, with each tithi representing a 12-degree separation. There are 30 tithis in a lunar month, but their duration varies between 19 and 26 hours due to elliptical orbits and orbital perturbations. This variability causes tithis to sometimes change during a single day, leading to different interpretations about which tithi governs a particular day. Thus, the Indian calendar system is a sophisticated integration of lunar and solar cycles, astronomical observations, and cultural practices, enabling the precise timing of festivals, rituals, and daily activities. **Table on page 4 (12×2)** | Caitra | चैत्र | | --- | --- | | Vaiśākha | वैशाख | | Jyēṣṭha | ज्येष्ठ | | Āṣādha | आषाढ़ | | Śrāvaṇa | श्रावण | | Bhādrapada | भोष्ट्याद | | Āśvina | आश्विन | | Kārtika | कार्तिक | | Agrahāyaṇa | अग्रहायण | | Pauṣa | पौष | | Māgha | माघ | | Phālguna | फाल्गुन | **Table on page 17 (7×2)** | Sūryasiddhānta | Moon | | --- | --- | | Lunar Year | Jantar Mantar observatories | | Nakśatras | Varāhamihira | | Nilkantha | 354 days | | Rāśi | Udaipur | | GONG | Ecliptic | | Jai Singh | Heliocentric solar system |

• The Hindu calendar is lunisolar, combining lunar months and solar months.
• Lunar month has two halves: Kṛṣṇapakṣa (dark) and Śuklapakṣa (bright), each about 15 days.
• Solar months correspond to the sun's passage through 12 zodiacal constellations (Rāśis).
• Nakṣatras are 27 or 28 prominent stars used to track the moon's position.
• An extra lunar month (adhikamāsa) is added every ~3 years to align lunar and solar years.
• Tithi is a lunar date based on the angular separation between sun and moon, varying in duration.
• 📌 Lunisolar calendar: A calendar based on both lunar phases and solar year.
• 📌 Sidereal period: Time taken by a celestial body to orbit relative to fixed stars.
• 📌 Synodic period: Time taken for a celestial body to return to the same phase as seen from Earth.