Eclipses in the Indian sky: what is computed and what is kept

Two kinds of shadow

A solar eclipse happens at new Moon (Amāvāsyā), when the Moon passes between the Earth and the Sun and hides some or all of the Sun's disc. A lunar eclipse happens at full Moon (Pūrṇimā), when the Moon passes through the Earth's shadow. Both are possible only when the new or full Moon falls near one of the two points where the Moon's tilted orbit crosses the Sun's path, the ecliptic. In Jyotisha these points are Rāhu, the ascending node, and Ketu, the descending node, always opposite each other.

The nodes drift slowly backwards around the ecliptic, so eclipses come in "seasons" a little under six months apart, with between four and seven eclipses in a calendar year. Our computation for 2026 gives four: an annular solar eclipse on 17 February, a total lunar eclipse on 3 March, a total solar eclipse on 12 August and a partial lunar eclipse on 28 August. Of these, only the lunar eclipse of 3 March is visible from New Delhi, where the Moon rises already in eclipse.

The story and the explanation

The Puranic story tells of the asura Svarbhanu, who drank the nectar of immortality by stealth and was beheaded by Vishnu; his head, Rahu, pursues the Sun and the Moon and swallows them from time to time. Grahana, the Sanskrit word for eclipse, means "seizing".

The astronomers gave a different account. Āryabhaṭa, in the Aryabhatiya (499 CE), states that the Moon covers the Sun and that the Earth's shadow covers the Moon. Varāhamihira, in the Brihat Samhita (6th century), sets out the shadow explanation at length and treats the story as belonging to another register: Rahu, he says, is present at an eclipse by a boon, but is not its cause†. Later siddhantas take the shadow account as their starting point. In their usage, Rahu and Ketu are mathematical points whose longitude enters the computation.

What the siddhantas compute

The Siddhānta texts, works of mathematical astronomy such as the Sūrya Siddhānta and Bhaskara II's Siddhanta Shiromani (1150), treat the lunar and the solar eclipse in separate chapters. The procedure, in outline:

• Find the true longitudes of the Sun, the Moon and the node at the new or full Moon, and from them the Moon's latitude.
• Compute the angular diameters (bimba) of the Sun and the Moon and, for a lunar eclipse, of the Earth's shadow (tamas).
• Compare the Moon's latitude with the sum of the semi-diameters to see whether an eclipse occurs and how much of the disc is covered (grasa).
• Compute the half-duration (sthityardha) and, for a total eclipse, the half-duration of totality (vimardardha).
• For a solar eclipse, correct for parallax in longitude and latitude (lambana and nati), since the observer stands on the Earth's surface, not at its centre.

The results are given as three moments: sparsha (first contact), madhya (middle) and moksha (release). When the Moon rises already eclipsed the texts call it grastodaya; when it sets eclipsed, grastasta. Modern computation uses the same geometry with refined constants and orbital theory; the canons compiled by Fred Espenak and Jean Meeus list the eclipses of five thousand years.

Where an eclipse is seen

A lunar eclipse happens at the same instant for everyone; whether it is seen depends only on whether the Moon is above the local horizon. A solar eclipse differs from place to place in its times, its extent and whether it occurs at all. The texts therefore speak of an eclipse as drishya, visible, or not, at a given place, and the rules of observance apply only where it is seen.

Grahana in the wider literature

The Saṃhitā skandha, the branch of Jyotisha concerned with collective matters and omens, reads eclipses as signs for kingdoms and seasons, and Varahamihira devotes long passages to such readings. We describe them as part of the history of the subject, not as forecasts. The Dharmashastra literature treats an eclipse as a sacred time, a punya kala, for bathing, prayer and giving.

Sutak, a practice that varies

Sutak (Sanskrit sutaka) is a period of ritual restriction before an eclipse. Dharmashastra digests such as Kamalakara Bhatta's Nirnaya Sindhu give it as four prahara (watches of about three hours, so about twelve hours) before a solar eclipse and three prahara (about nine hours) before a lunar one. During it cooking and eating are set aside and many temples close; the digests relax these rules for children, the elderly and the sick†. Practice varies widely: some families keep only the eclipse itself, some count from sparsha, and communities differ in what they set aside†. By the texts' own rule, sutak applies only where the eclipse is visible.

We report sutak as a practice recorded in the texts and kept by many families. It is not a claim about any effect of eclipses on people.

Watching safely

A lunar eclipse can be watched freely with the naked eye. A solar eclipse cannot: the Sun should never be looked at directly, even when it is mostly covered. Use certified eclipse filters or a pinhole projection.

Try it

The Eclipses page lists every eclipse of the year, with the phases in Indian Standard Time, visibility from Indian cities and, where an eclipse is visible, the sutak span by the texts' rule. The Panchang shows the new and full Moons around which eclipses can occur.

† Marked dates or readings are debated among scholars or still being confirmed by our faculty.