We usually calculate the day of the sun? The year of return?

There are three kinds of years: the earth revolves around the sun for 365 days, 6 hours, 9 minutes and 9 seconds, which is called "sidereal year"; The year of perigee is called "perigee year", when the sun passes perigee and travels eastward along the ecliptic, and then passes perigee at 6: 13: 48 in 365 days. The sun crossed vernal equinox, followed the ecliptic to the east, and then crossed vernal equinox, which lasted for 365 days, 5 hours, 48 minutes and 46 seconds. It was called "the year of the Tropic of Cancer", also known as "the year at the end of the year".

Because the vernal equinox (vernal equinox and autumnal equinox) retrogrades westward along the ecliptic for about 50 seconds every year, the time of the return year is shorter than that of the sidereal year, with a difference of 20.23 seconds, which is called "precession".

These three years are different. In order to keep the solar terms hot and cold every year, the tropic year is chosen as the Gregorian calendar year.

1 sidereal day =23 hours, 56 minutes and 4.09894 seconds.

solar day

Astronomically speaking, the unit of time, that is, the time it takes the earth to face the sun twice on the same meridian, is 24 hours.

So what you said is correct. We usually calculate the solar day, the year of the Tropic of Cancer.