The Sun’s declination reaches about +23.5 degrees at the Northern Hemisphere summer solstice.
Declination is the celestial equivalent of latitude: it measures how far north or south an object appears from Earth’s celestial equator. At the June solstice, the Sun reaches its greatest northern declination because Earth’s North Pole is tilted maximally toward the Sun.
The precise modern value is approximately +23.44 degrees, known as the obliquity of the ecliptic. Trivia references commonly round this to +23.5 degrees. The Sun’s direct rays then fall on the Tropic of Cancer, whose latitude is also approximately 23.5 degrees north.
This value is not permanently fixed. Earth’s axial tilt changes slowly over a cycle of roughly 41,000 years, so the maximum declination varies slightly over geological time. The Southern Hemisphere’s summer solstice has the opposite value, approximately −23.44 degrees.