Meanwhile, astronomical seasons are based on the position of the Earth in relation to the sun.
This year, astronomical summer starts June 21, the date of the summer solstice. This date typically varies between June 21 or 22, depending on the solstice.
Astronomical winter also varies between Dec. 21 or 22, the date of the solstice. Spring and fall both depend on the vernal and autumnal equinoxes.
Since it takes 365.25 days for the earth to travel around the sun, an extra day is needed every four years, known as Leap Year. This can cause the dates of solstices and equinoxes to vary.
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That, combined with the fact that the elliptical path of the Earth around the sun can cause the length of the path and seasons to be inconsistent, makes keeping climatological statistics confusing year-to-year.