Solstice

A solstice is one of the two annual moments when the Sun reaches its greatest north or south declination, marking the longest or shortest daylight period of the year.

Earth's axial tilt: Earth's rotation axis is tilted about 23.4 degrees relative to the perpendicular to its orbital plane. This tilt shifts the Sun’s apparent path north and south through the year.
Tropic of Cancer: The Tropic of Cancer is the northernmost latitude where the Sun can appear directly overhead at noon. The June solstice places the Sun overhead at this latitude.
Tropical year: A tropical year is the time Earth takes to complete a cycle of seasons, measured between successive vernal equinoxes. Solstices recur within this seasonal cycle, whose length sets their approximate annual timing.
Midsummer: Midsummer is a seasonal celebration associated with the summer solstice in parts of Europe and elsewhere. Its timing centers on the year’s greatest daylight in the Northern Hemisphere.
Ecliptic: The ecliptic is the apparent annual path of the Sun across the celestial sphere. Solstices occur where the Sun’s apparent path reaches its greatest celestial latitude from the equator.
Tropic of Capricorn: The Tropic of Capricorn is the southernmost latitude where the Sun can appear directly overhead at noon. The December solstice places the Sun overhead at this latitude.
Precession of the equinoxes: Precession of the equinoxes is the slow change in the orientation of Earth's rotation axis relative to the stars. It shifts the seasonal points against the background constellations over millennia.
Yule: Yule is a midwinter festival with Germanic roots, later incorporated into Christmas traditions. Its seasonal setting is near the December solstice in the Northern Hemisphere.
Celestial equator: The celestial equator is Earth’s equator projected outward onto the celestial sphere. The Sun’s maximum and minimum declinations are measured relative to this circle.
Arctic Circle: The Arctic Circle is the southernmost latitude at which the Sun can remain above the horizon for a full day. The June solstice brings continuous daylight within the circle.

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