Editing Content :: Admin Scraper

Chapter

Content type

Position

Value

11.2.2 Solar calendars It was important to know the arrival of seasons for agricultural purposes. This need for a year to synchronise with seasons led to the creation of solar calendars. The Gregorian calendar, widely used today, is a solar calendar. The months in solar calendars are adjustedtoaddupto365days.ThatiswhyinGregoriancalendars, some months have 30 days, others 31, and February has only 28 days. On top of the 365 days, the Earth tak es nearly an extra quarter of a day to complete one revolution around the Sun. These extra hours add up to approximately one day every four years. To adjust for this, solar calendars add an extra day every four years using the concept of a leap year. In the Gregorian calendar, if a year is divisible by four, then an extra leap day is added. So in a leap year, February has 29 days, which keeps the calendar well synchronised with the seasons. A step further The Earth takes slightly less time than 365 and a quarter day to go from one spring equinox to the next spring equinox. Adding a day every four years helps to synchronise with the seasons, but it actually adds a little too much over time. To fix this, leap years are skipped every 100 years—like in 1700, 1800, and 1900. But skipping all of them would make the calendar lag slightly behind. So every 400 years, a leap year is again added back—like in 1600 and 2000. These careful corrections keep the calendar closely matched with the seasons over long periods of time! A step further As we learnt earlier, seasons are caused by the Earth’s revolution around the Sun and its movement from the spring equinox to winter equinox and back. The time between successive spring equinoxes is called the tropical year. Gregorian calendar is based upon tropical year. We have also learnt earlier that the stars that rise at sunset change throughout the year due to the Earth’s revolution around the Sun. The time duration required for the same stars to rise again at sunset is called the sidereal year, and it can also be used to define a solar calendar. The sidereal year is longer than the tropical year by a mere 20 minutes, and so it takes a long time before the differences between the two calendars become noticeable. In modern times, astronomers use the sidereal year to keep track of the Earth’s position in its orbit around the Sun. 180 Curiosity — Textbook of Science for Grade 8 Reprint 2026-27