NCERT Solutions for Class 8th Science Chapter 11 .3 Are Festivals Related to Astronomical Phenomena? — In-text Questions
Book page 18311 Updated on2026-09-19
Q1.
Why do most Indian festivals fall on different dates every year?
Answer
Because most Indian festivals are fixed by the phase of the Moon, while the dates we quote come from the Gregorian solar calendar — and a lunar year and a solar year are not the same length.
12 lunar months = 12 × 29.5 ≈ 354 days 1 solar year ≈ 365 days Shortfall each year = 365 − 354 = about 11 days
What happens next depends on which kind of calendar the festival follows.
Kind of calendar
Example festivals
How the Gregorian date behaves
Purely lunar
Eid-ul-Fitr, after the crescent Moon is sighted at the end of Ramazan
Moves about 11 days earlier every year and drifts right through all the seasons — it can fall in any Gregorian month
Luni-solar
Diwali (new Moon of Kartika), Holi (full Moon of Phalguna), Buddha Purnima (full Moon of Vaisakha), Dussehra (tenth day of Ashwina)
Moves about 11 days earlier, but an Adhika Maasa every 2–3 years pushes it back by a month. So it wanders within a window of about a month and never leaves its season
Falls on almost the same Gregorian date every year
Why a luni-solar festival wobbles but never drifts away: the 11-day annual shortfall is cancelled by an extra month every two or three years.
Why it happens: A festival tied to the Moon has a fixed lunar date but no fixed solar date. Since 12 lunar months are 11 days short of a solar year, that lunar date must arrive 11 days earlier on the Gregorian calendar each time. The intercalary month is exactly the correction that stops the drift — which is why Diwali always stays in the autumn while Eid-ul-Fitr can fall in any season.
Did you know? Because these dates are decided by the exact lunar phase at sunrise, and the Sun rises earlier in eastern India than in western India, a festival can even fall on different days in different parts of the country in the same year. To keep things uniform, the Positional Astronomy Centre publishes the Rashtriya panchang every year.