Winter Solstice – The Shortest Day

The winter solstice (around Dec 21) is the shortest day of the year in the Northern Hemisphere. The axial tilt of 23.5° causes the Sun’s declination to reach –23.5°. At the Arctic Circle, the Sun does not rise. The length of day can be calculated by spherical trigonometry: cos(H) = –tan(φ) tan(δ). For London (51.5°N), the day length is about 7 hours 50 minutes. The solstice is a turning point – days get longer. Ancient monuments like Newgrange align with the solstice sunrise. Mathematics celebrates the return of light.