The Fascinating History of Leap Days

TLDRLearn about the history and purpose of leap days, which balance our calendar with Earth's orbit. Every four years, we add an extra day to ensure our calendar aligns with the solar year. However, every century year that is not divisible by 400 does not have a leap day. The Gregorian calendar, implemented in 1582, adjusted the calendar to account for these discrepancies.

Key insights

🗓️Leap days are added to the calendar every four years to account for the time it takes for Earth to orbit once around the sun.

📅Century years that are not divisible by 400 do not have a leap day, ensuring the long-term accuracy of the calendar.

🔀Before the implementation of the Gregorian calendar in 1582, there were inaccuracies in the Julian calendar that led to a misalignment with the vernal equinox.

⏳An undercorrection of the calendar over centuries caused the vernal equinox to shift earlier in the year, necessitating the adjustment in the Gregorian calendar.

🎉Leap days are an interesting and necessary leap year tradition, marking a unique occurrence that happens only once every four years.

Q&A

Why do we have leap days?

—Leap days are added to our calendar every four years to ensure that our calendar aligns with Earth's orbit around the sun.

Do all years have a leap day?

—No, only years divisible by four have a leap day, except for century years that are not divisible by 400.

What is the purpose of the Gregorian calendar?

—The Gregorian calendar was implemented to correct inaccuracies in the Julian calendar that led to a misalignment with the vernal equinox.

Why is the vernal equinox important?

—The vernal equinox marks the first day of spring in the Northern Hemisphere and is used as a reference point for determining the date of Easter.

Why is it called a leap day?

—The term 'leap day' refers to the additional day added to the calendar, which causes it to 'leap' over a regular day.

Timestamped Summary

00:00In this video, Neil deGrasse Tyson and Chuck Nice discuss the history and purpose of leap days.

03:40Leap days are added to the calendar every four years to ensure that our calendar aligns with Earth's orbit around the sun.

06:00Century years that are not divisible by 400 do not have a leap day, correcting for the slight inaccuracies in our calendar.

09:45The implementation of the Gregorian calendar in 1582 fixed the inaccuracies of the Julian calendar and reset the alignment with the vernal equinox.

10:50Leap days are symbolic and interesting, marking a special occurrence that happens only once every four years.

Browse more