Recently we presented an article on the six definitions of a year. A year is not necessarily a year. “Annual” means yearly, but what is a year? There are actually 6 different years: Anomalistic year, Draconitic year, Julian year (this one you are familiar with — 365.25 days), Luna year, Sidereal year, and Tropical year.
A tropical year is the time it takes for the Sun to travel 360° along the ecliptic, its apparent path through the sky. Since the Sun doesn’t actually go around Earth, this should be restated as the time it takes Earth to complete a full orbit around the Sun. It varies from year to year, but to 8 significant figures it is 365.24219 days. 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.
The chart below shows the lengths of each of the years in days. Note how much shorter than the Calendar Year is the Sidereal Year—just a
It surprises people that our common conception of how to measure time is not precisely fixed, and there is the question: “A year is a year is a year?”