And instead of racing ahead on our calendar by another 45 minutes from 1896 to 1900, we instead let the calendar "catch up" by a full 23 hours and 15 minutes by not having a Leap Year.
But that's the huge advantage of the Gregorian Calendar over the Julian Calendar: years that end in "hundred" are only Leap Years if they're divisible by 400.ġ900, therefore, wasn't a Leap Year. And all of this would have continued to get worse all through the 20th century if we had made 1900 a Leap Year as well. Irv Bromberg / University of TorontoĬompared to 1800, therefore, the 1896 calendar year saw an equinox that was approximately 18 hours earlier than the 1800 equinox. The slow migration of the various 'lines' correspond to four year intervals, with the discontinuities accounted for by non-Leap centuries.
except during a leap year, where it jumps in the other direction by approximately 18 hours. Each time we make that approximation - that 1-in-4 years are a Leap Year - we wind up keeping time "too fast" by about 45 minutes every four years.Įvery year, the time at which the equinox occurs shifts by nearly six hours over the previous year. Remember, with 365.242189 days required to account for a full year, approximating that by having a Leap Year every four years (which is an average of 365.25 days-per-year) actually puts us a little bit ahead. In terms of a calendar, 1896 was the last Leap Year in a string of 24 consecutive every-four-years Leap Years, from 1804 to 1896, inclusive. Think about the significance of that year: 1896. In fact, the last year that saw a March 19 equinox, or any equinox as early as 2020 will experience, was 1896. Pixabay user annevaisĪnd yet, those of us who remember growing up and living a substantial portion of our lives in the 1900s quite accurately remember that the 20th century never had a March equinox on the 19th. which will mean that on March 19, 2020, the equinox will occur everywhere in the United States on that date. As a result, 2020's equinox occurs about 18 hours earlier than 2019's did: enough to push it back to March 19 for all United States timezones.īy changing our clocks on Sunday March 8, we'll shift the United States onto Daylight Saving Time. Whereas "only" an extra 0.242189 days (about 5 hours and 49 minutes) needed to be added to our calendar to keep 2020 in line with where we were in 2019, we instead added a whole entire 24-hour day. The reason it's so much earlier this year as compared to last year is because of the insertion of Leap Day this past February 29th. In 2019, for example, the March equinox occurred in the United States on March 20, at 5:58 PM ET (2:58 PM PT): some 18 hours later than it's occurring in 2020. NASA / JPLīut getting something precisely right on average doesn't mean it's going to be exactly the same year after year or century after century. However, the time to complete one complete orbit is not exactly an integer number of days, and so our calendar shifts with respect to the true celestial calendar depending on the number of days we place in any given year.
The speed at which planets revolve around the Sun is dependent on their distance from the Sun.
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