Longest Night of the Year

Every year someone insists the longest night falls on 21 June, and it does not always. The solstice is an astronomical instant that drifts by hours from one year to the next and sometimes slips across midnight. Pick a year and a hemisphere and the page returns the date of the matching winter solstice: June for the Southern Hemisphere, December for the Northern.

The engine is Jean Meeus's approximation, a polynomial for the mean solstice instant corrected by 24 periodic terms that fold in planetary perturbations and orbital eccentricity. Nothing is looked up from a table, so any year from 1000 to 3000 produces an answer. You get the date of that instant in UTC with a copy button, and a fixed panel underneath repeating the 2024 to 2026 dates. Month names and the hemisphere selector print in Portuguese.

The UTC tag at the end of the result matters. In 2025 the June solstice fell on 21/06 at 02:43 UTC, which in Brasilia time was 20/06 at 23:43, so the longest Brazilian night ran from the 20th into the 21st. Whenever the instant lands in the small hours UTC, subtract your offset before announcing a date. The page gives the day of the solstice, not the length of the night, which depends on a latitude it never asks for. The computation happens in your browser.