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How Long Is a Tropical Year / Solar Year?

The length of a tropical year is the time it takes for the seasons to repeat—roughly the time it takes the Earth to complete an orbit around the Sun.

Illustration image
Illustration image

A tropical, common, and leap year.

A Year Is Never 365 Days Long

A tropical year, also known as a solar year, an astronomical year, or an equinoctial year, is, on average, approximately 365 days, 5 hours, 48 minutes and 45 seconds long (365.24219 days).

A tropical year can be measured from either the vernal or autumnal equinox to the next one, or from the Summer or the winter solstice to the next one.

On timeanddate.com, we calculate a tropical year from the March equinox to the next March equinox (see table below).

Leap Day Synchronizes Calendar

Although a common year has 365 days in today's Gregorian calendar, we add a leap day nearly every four years to stay in sync with the tropical year.

Without the correct amount of leap years, our calendar would quickly become out of sync. This happened to the Julian calendar, which had too many leap years. Eventually, it was replaced with the Gregorian calendar.

Can Vary by 30 Minutes

The exact length of a tropical year can vary by up to around half an hour. For instance, the tropical year 2032 will last longer than 365 days and 6 hours. 2027, however, will only last 365 days, 5 hours, and 39 minutes.

List of all tropical years 1900–2100

Length of Tropical Year 2010–2030

Tropical year measured from/to the March equinox. Accuracy believed to be within a few seconds. Leap seconds are accounted for.

March 2010 – March 201136554823
March 2011 – March 201236555356
March 2012 – March 201336554722
March 2013 – March 201436555514
March 2014 – March 20153655482
March 2015 – March 201636554456
March 2016 – March 201736555836
March 2017 – March 201836554641
March 2018 – March 201936554312
March 2019 – March 20203655514
March 2020 – March 202136554755
March 2021 – March 202236555554
March 2022 – March 202336555055
March 2023 – March 20243655428
March 2024 – March 202536555453
March 2025 – March 202636554439
March 2026 – March 202736553839
March 2027 – March 202836555227
March 2028 – March 202936554457
March 2029 – March 203036554956

Tropical Year versus Sidereal Year

A tropical year is roughly—but not exactly—the time it takes the Earth to complete one orbit around the Sun.

Because the orientation of Earth’s tilt has a slight wobble (a motion called precession), the time from one March equinox to the next is a fraction shorter than Earth’s orbital period around the Sun.

The time for one orbital revolution around the Sun is called a sidereal year—this is approximately 365.25636 days.

Topics: Calendar, Leap Year, Astronomy, Seasons