Tropical Year (yr (trop))

AstronomicalCurrent unitApproximate value

About 365.24219 days, the time between successive spring equinoxes. The Gregorian calendar approximates it.

1 tropical year = 31,556,925.22 seconds (approximately).

Approximate value. Standards for the tropical year varied by place and period, so this converter uses the most commonly cited value. Treat results as estimates, not exact figures.

About the tropical year

Tropical comes from a Greek word meaning turning, and this year is measured by the cycle of the seasons: the time for the Sun to return to the same ecliptic longitude. The mean value at the start of 2000 was 365.2421897 days, or 365 days 5 hours 48 minutes 45.19 seconds. Individual intervals between March equinoxes wander by minutes, so the mean is what is normally quoted.

Hipparchus timed equinoxes in the second century BC and arrived at 365 days 5 hours 55 minutes 12 seconds, a little long. The Alfonsine Tables of 1252 gave 365 days 5 hours 49 minutes 16 seconds, and this value guided the Gregorian reform of 1582, which was needed because the equinox had slipped about ten days from its date at the Council of Nicaea in 325.

Kepler's Rudolphine Tables of 1627 came within a second or so of the modern figure, and Simon Newcomb's 1898 value of about 365.24219878 days served the national almanacs until 1983. The Gregorian calendar averages 365.2425 days, which tracks the tropical year closely.

Sources: Wikipedia: Tropical year; NASA Earth Fact Sheet

Tropical Year conversion chart

1 tropical year expressed in every other time unit:

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