A solstice is either of the two events of the year when the sun is at its greatest distance from the equatorial plane. The name is derived from Latin sol (sun) and sistere (to stand still), because at the solstice, the Sun stands still in declination, that is, it reaches a maximum or a minimum. The term solstice can also be used in a wider sense as the date (day) that such a passage happens. The solstices, together with the equinoxes, are related to the seasons. In some languages they are considered to start or separate the seasons; in others they are considered to be center points (in English, in the Northern hemisphere, for example, the period around the June solstice is known as midsummer, and Midsummer's Day is the 24 June — now two or three days after the solstice).

Summer solstici Sun imaged from Tican hill at AstroFest 2006                                                                       Image: G. Kervina

The two solstices can be distinguished by different pairs of names, depending on which feature one wants to stress:

• Summer solstice and winter solstice are the most common names. However, these can be ambiguous since seasons of the northern hemisphere and southern hemisphere are opposites, and the summer solstice of one hemisphere is the winter solstice of the other.

• Northern solstice and southern solstice indicate the direction of the sun's movement. The northern solstice is in June on Earth, when the sun is directly over the Tropic of Cancer in the Northern Hemisphere, and the southern solstice is in December, when the sun is directly over the Tropic of Capricorn in the Southern Hemisphere. Some consider these terms to be the most neutral and unambiguous.

• June solstice and December solstice are an alternative to the more common "summer" and "winter" terms, but without the ambiguity for which hemisphere they are intended. They are still not universal, however, as not all people on Earth use a solar-based calendar where the solstices occur every year in the same month (as they do not in the Jewish calendar, for example), and the names are also not useful for other planets (Mars, for example), even though these planets do have seasons.

• First point of Cancer and first point of Capricorn. One disadvantage of these names is that, due to the precession of the equinoxes, the astrological signs where these solstices are located no longer correspond with the actual constellations.

• Taurus solstice and Sagittarius solstice are names that indicate in which constellations the two equinoxes are currently located. These terms are not widely used, though, and until December 1989 the first solstice was in Gemini, according to official IAU boundaries.