Year: 1) The period during which the Earth completes one revolution around the sun. This has several interpretations. a) Sidereal Year: Time of true revolution around the sun--that is, the time it takes the Earth (as seen from the sun) to reappear at the same fixed star, equal to 365.2564 mean solar days or 365 days, 6 hours, 9 minutes, 10 seconds. b) Tropical Year: The time measured from one vernal equinox to the next--that is, the apparent revolution of the sun through the zodiac, equal to 365.2422 mean solar days or 365 days, 5 hours, 48 minutes, 46 seconds. This is not a constant, but only decreases by 5 seconds in every one thousand years. This is also called mean solar year or ordinary year. c) Calendar Year: Fixed by the Gregorian calendar of 365 days in an ordinary year and 366 days in leap year. 2) Any arbitrary 12-month period selected for a special purpose, such as the water year.
Yellow Snow: Snow given a golden or yellow appearance by the presence in it of pine, cypress pollen, or anthropogenic material or animal-produced material. Compare with Brown Snow.