# Hindu Sunrise

> How Hindu sunrise (Surya Udaya) is astronomically determined, why the Hindu day runs from sunrise to sunrise, and its role in Udayatithi.

Source: https://www.hinducalendar.today/sa/panchang/sunrise/panchang-sunrise

| Definition | First appearance of the Sun's upper limb on the visible horizon |
| --- | --- |
| Atmospheric Effects | Adjusted for terrestrial refraction and solar semi-diameter (about 50 arcminutes) |
| Hindu Day (Ahoratra) | Runs from local sunrise to next local sunrise (Dinadhisha) |
| Key Principle | Udayatithi: the tithi prevailing at sunrise governs festival observance |

## Astronomical definition of Hindu sunrise

In classical Siddhantic astronomy (including the Surya Siddhanta and modern Drik Ganita calculations), sunrise is defined as the precise instant when the upper edge of the Sun's disc becomes visible above the apparent horizon for an observer on Earth. This requires correcting for both atmospheric refraction (which bends light rays so the Sun appears before it crosses the geometric horizon by about 34 to 36 arcminutes) and the Sun's semi-diameter (approximately 16 arcminutes).

Together, these corrections cause the Sun to appear approximately 50 arcminutes higher than its true geometric centre. Furthermore, the observer's altitude above sea level and local horizon dip must be factored in for exact regional ephemerides.

## The day from sunrise to sunrise (Ahoratra)

The Vedic calendar divides each complete day-and-night cycle (Ahoratra) into two principal spans: Dinamana (the period from sunrise to sunset) and Ratrimana (the period from sunset to the next sunrise). Because the Sun's declination shifts throughout the solar year and varies with geographic latitude, the lengths of daytime and nighttime continuously evolve across seasons.

Crucially, all thirty Muhurtas (each lasting two ghatis, or roughly 48 minutes on an equinox day), as well as the eight day Choghadiyas and seven planetary Horas, are measured directly from the time of local sunrise.

## The rule of Udayatithi in festival observance

The most pervasive application of Hindu sunrise is the principle of Udayatithi: the lunar day (tithi) that is actively prevailing at the exact moment of local sunrise is considered the presiding tithi of that civil day for most sacred vows, fasts, and religious rites.

Even if a tithi ends just a few minutes after sunrise, the entire day is liturgical counted under that tithi. Conversely, a tithi that begins after sunrise and ends before the following dawn is known as a Kshaya tithi (lost tithi), illustrating why localized sunrise calculations are paramount for spiritual calendar accuracy.

## तिथयः सम्बद्धपृष्ठानि च

- [Hindu Panchangs](https://www.hinducalendar.today/sa/panchang/hindu-panchangs)
- [Muhurat](https://www.hinducalendar.today/sa/muhurat/muhurat)
- [Panchang Utilities](https://www.hinducalendar.today/sa/panchang/panchang-utilities)
- [Start and End Times in the Panchang](https://www.hinducalendar.today/sa/faq/faq-ans1)

## Panchang Concepts

- [Agnivasa](https://www.hinducalendar.today/sa/panchang/info/agnivasa/agnivasa)
- [Shivavasa](https://www.hinducalendar.today/sa/panchang/info/shivavasa/shivavasa)
- [Bhadravasa](https://www.hinducalendar.today/sa/panchang/info/bhadravasa/bhadravasa)
- [Homahuti](https://www.hinducalendar.today/sa/panchang/info/homahuti/homahuti)
- [Manvadi Days](https://www.hinducalendar.today/sa/panchang/tithi/manvadi/manvadi-days)
- [Yugadi Days](https://www.hinducalendar.today/sa/panchang/tithi/yugadi/yugadi-days)
- [Kalpadi Days](https://www.hinducalendar.today/sa/panchang/tithi/kalpadi/kalpadi-days)
- [Jwalamukhi Yoga](https://www.hinducalendar.today/sa/panchang/yoga/jwalamukhi/jwalamukhi-yoga)
- [Times Avoided for Marriage](https://www.hinducalendar.today/sa/panchang/yoga/prohibited-marriage-yoga)
- [Kartika Month](https://www.hinducalendar.today/sa/panchang/lunar-month/kartika/kartika-month)
- [Shravana Month](https://www.hinducalendar.today/sa/panchang/lunar-month/shravana/shravana-month)
- [Sankalpa](https://www.hinducalendar.today/sa/panchang/sankalpa/sankalpa)
- [Panchang Utilities](https://www.hinducalendar.today/sa/panchang/panchang-utilities)
- Hindu Sunrise
- [Tarabalam Timings](https://www.hinducalendar.today/sa/panchang/tarabalam/tarabalam-timings)
- [Printed Panchangs](https://www.hinducalendar.today/sa/panchang/info/paper-almanacs/famous-published-panchang)
- [Upagraha Dosha](https://www.hinducalendar.today/sa/panchang/dosha/surya-chandra/upgraha-dosha)
- [Panchang Shuddhi](https://www.hinducalendar.today/sa/panchang/panchang-dina-shuddhi)
- [Kalnirnay Panchang](https://www.hinducalendar.today/sa/panchang/info/paper-almanacs/kalnirnay/kalnirnay-panchang)
- [Kaldarshak Panchang](https://www.hinducalendar.today/sa/panchang/info/paper-almanacs/kaldarshak/kaldarshak-panchang)
- [Thakur Prasad Panchang](https://www.hinducalendar.today/sa/panchang/info/paper-almanacs/thakur-prasad/thakur-prasad-panchang)
- [Kashi Vishwanath Panchang](https://www.hinducalendar.today/sa/panchang/info/paper-almanacs/kashi-vishwanath/kashi-vishwanath-panchang)
- [Chintaharan Jantri Panchang](https://www.hinducalendar.today/sa/panchang/info/paper-almanacs/chintaharan-jantri/chintaharan-jantri-panchang)