The Earth takes 365¼ days to revolve around the Sun.
Explanation
The Gregorian calendar is a solar calendar designed to synchronize with the Earth's revolution around the Sun. The necessity of a leap year arises from the difference between the calendar year and the actual solar year.Detailed Analysis:
- The Earth's orbit is elliptical. is incorrect: While the Earth's orbit is elliptical, determining the changing distance from the Sun (perihelion and aphelion), the shape of the orbit does not create the fractional time difference that necessitates a leap year.
- The Earth takes 365¼ days to revolve around the Sun. is correct: The Earth takes approximately 365.2422 days (roughly 365¼ days) to complete one full revolution around the Sun. A standard calendar year consists of exactly 365 days. The extra fraction of a day (~0.25 days) accumulates each year. To compensate for this lag and keep the calendar aligned with the Earth's position in relation to the Sun, an extra day is added every four years (0.25 × 4 = 1 day).
- The Earth's axis is tilted. is incorrect: The tilt of the Earth's axis (approximately 23.5°) is the primary cause of the seasons (summer, winter, etc.) and the variation in day length, but it is not the reason for the leap year adjustment.
- The Moon's gravitational pull. is incorrect: The Moon's gravitational pull is responsible for the tides in the Earth's oceans. It does not determine the length of the solar year or the structure of the solar calendar.
Key Takeaway: Leap years are inserted to correct the discrepancy between the calendar year (365 days) and the astronomical solar year (~365¼ days), ensuring that seasons remain fixed in the calendar over long periods.