Why Karva Chauth Moonrise Differs by Up to an Hour Across Indian Cities

On Karva Chauth, a woman in Kolkata lifts her sieve to the Moon while her sister in Mumbai is still waiting. The gap between their moonrises can stretch past sixty minutes, not because of different traditions, but because of where each city sits on Earth and how the Moon moves.

India spans roughly 30 degrees of longitude, from the Rann of Kutch in the west to Arunachal Pradesh in the east. Earth rotates 15 degrees per hour, so a location 30 degrees to the east sees any celestial object rise about two hours earlier than a location at the far west. Kolkata sits near 88°E; Mumbai near 73°E. That 15-degree difference alone pushes Kolkata's moonrise roughly one hour ahead of Mumbai's. India uses a single standard time, IST, which is UTC+5:30, anchored to 82.5°E near Allahabad. Cities east of that meridian experience moonrise earlier in clock time; cities west of it experience it later. When the Karva Chauth moonrise table lists 8:09 PM for Delhi and 9:11 PM for Mumbai, longitude is doing most of that work.

The Moon does not rise at the same time each night. It orbits Earth in the same direction Earth rotates, so the Moon falls behind the Sun's apparent motion by about 50 minutes each day, meaning moonrise is roughly 50 minutes later every successive night. But that average conceals real variation. The Moon's orbit is tilted about 5 degrees relative to Earth's orbital plane, and the ecliptic, the path the Sun and Moon follow across the sky, meets the horizon at different angles depending on the season and the observer's latitude. In autumn at Indian latitudes, the ecliptic meets the eastern horizon at a shallow angle. The Moon's daily eastward drift along the ecliptic therefore carries it only a short distance below the horizon compared to how far it moves along the horizon itself. The result: in October, consecutive moonrises in northern India can be as little as 30 minutes apart rather than the average 50. This is the same geometry that produces the Harvest Moon effect in temperate latitudes, several nights of nearly same-time moonrise. For Karva Chauth, it means the Moon rises only modestly later than the night before, which is why the festival falls on a chaturthi, the fourth day after the full moon, when the Moon is still large and rises at a civilised hour of the evening.

The moonrise time for any city is computed from three inputs: the city's latitude and longitude, the Moon's precise position in its orbit on that date, and the local horizon's elevation. Astronomical almanacs, and the Panchang, the traditional Hindu calendar, use spherical trigonometry to find the moment the Moon's upper limb clears the geometric horizon, then apply a standard atmospheric refraction correction of about 34 arcminutes, which bends the Moon's light so it appears above the horizon before it is geometrically there. The Panchang has carried these calculations for centuries using the Surya Siddhanta and later Siddhantic texts, which modelled the Moon's mean motion and its two main orbital corrections, the equation of centre and the evection, with enough accuracy to predict moonrise to within a few minutes. Modern ephemeris software such as NASA's HORIZONS system and the algorithms in Jean Meeus's Astronomical Algorithms refine the same calculation using updated orbital elements, but the structure of the problem is identical to what medieval Indian astronomers were solving at Jantar Mantar observatories in Jaipur and Delhi.

The ritual of viewing the Moon through a sieve, or first seeing its reflection in water or a thali, is sometimes explained as protecting the eyes. Astronomically, neither a sieve nor a water reflection reduces moonlight enough to matter, the Moon is roughly 400,000 times dimmer than the Sun and poses no eye hazard. The more grounded explanation is that the sieve frames the Moon in a defined circle, making it easier to locate in a bright urban sky where light pollution can wash out a not-quite-full Moon near the horizon. Viewing a reflection also lowers the effective viewing angle, which can be useful when buildings block the low eastern sky. The tradition likely evolved as practical guidance that acquired ritual meaning over generations.

Every reliable Karva Chauth moonrise table gives times in IST for specific cities. The time is for the Moon's upper limb clearing the geometric horizon at sea level; if you are in a high-rise or behind a ridge, add the extra angle that obstruction represents, roughly four minutes for every degree of effective horizon elevation. Mobile apps using GPS coordinates and the device's elevation data will give the most locally accurate figure. The Panchang published by the Drik Panchang platform and similar services calculates city-specific times from current ephemeris data and is considered reliable for this purpose. The key number to look for is not the chaturthi tithi start time but the moonrise time for your city on that specific calendar date, because the tithi and the moonrise are separate astronomical events that happen to coincide on Karva Chauth by the festival's design.