Tropical year

A tropical year (also known as a solar year) is the length of time that the Sun takes to return to the same position in the cycle of seasons, as seen from Earth; for example, the time from vernal equinox to vernal equinox, or from summer solstice to summer solstice. A tropical year can equivalently be defined as the time taken for the Sun's tropical longitude (longitudinal position along the ecliptic relative to its position at the vernal equinox... more

A tropical year (also known as a solar year) is the length of time that the Sun takes to return to the same position in the cycle of seasons, as seen from Earth; for example, the time from vernal equinox to vernal equinox, or from summer solstice to summer solstice. A tropical year can equivalently be defined as the time taken for the Sun's tropical longitude (longitudinal position along the ecliptic relative to its position at the vernal equinox) to increase by 360 degrees (that is, to complete one full seasonal circuit). For the reasons explained below, the length of a tropical year varies slightly, by up to a minute or two, depending on the seasonal starting point. The tropical year measured between (northern) vernal equinoxes (one of the four cardinal points along the ecliptic), is called the vernal equinox tropical year, or just vernal equinox year. The mean tropical year is calculated by averaging the (slightly differing) tropical years over all possible starting points through... less