Either of two points on the ecliptic, midway
between the equinoxes, at which the Sun
reaches its greatest northern declination
(summer solstice in the northern hemisphere, winter solstice in the southern,
on June 21) and greatest southern declination (vice versa, on December 22).
At these points occur the longest day and shortest night in one hemisphere
of the Earth, and vice versa in the other. The solstitial points
are the Sun's positions when it is momentarily stationary on these occasions.
The solstitial colure is the hour angle that passes through
the solstices on the celestial sphere.