Eli5 what is the point in leap years ,like why do we have them?
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The time it takes for the Earth to go around the Sun isn’t a whole number of days, it’s around 365.242. This means that for any year length you pick (say 365 days), when you reach midnight on New Years, the Earth will be slightly behind in its orbit compared to the last time around.
For a few years this isn’t much of an issue, but over long periods of time this leads to the calendar and seasons ‘drifting’ apart, we’d really prefer for them to stay synchronized. So every 4 years we insert an extra day, this makes the average year length 365.25 days, this slightly overshoots 365.242 so every 100 years we skip a leap year (so 1900 wasn’t a leap year, despite 1896 and 1904 being ones). This correction actually slightly undershoots so every 400 years we have a leap year despite the 100 years rule (so 2000 was a leap year, though 1900 and 2100 aren’t).
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