Methodology

Algorithm: sunrise and sunset use the NOAA Global Monitoring Laboratory solar-position equations (a published, public algorithm based on Jean Meeus’s Astronomical Algorithms): solar declination and equation of time for the date, then the hour angle at which the sun’s center is 0.833° below the horizon (standard allowance for atmospheric refraction and the sun’s radius), iterated for the event time. Accuracy of the algorithm is about a minute at mid-latitudes.

Places: 311 U.S. NOAA weather-station locations (the same places as our sister site First Snow Dates; mostly airports). Coordinates come from NOAA’s GHCN-Daily station list. Time zones come from the open timezonefinder database and Python’s IANA time-zone data, which handle daylight saving rules.

Earliest sunset: the day between Nov 2, 2026 and Jan 31, 2027 with the earliest local clock-time sunset (to the second, then displayed rounded to the minute). Because the minimum is very flat, the sunset is within a minute of its earliest for a week or two; each page shows that. Latest sunrise is the same for sunrise. Shortest day is the day with the least time between sunrise and sunset (Dec 21, 2026 in all places).

Sunset back at 5 pm: first day after the earliest sunset, before DST starts Mar 14, 2027, on which the minute-rounded sunset is 5:00 pm or later.

Checks: we spot-checked one city against a commercial sunrise/sunset reference: for Chicago it lists an earliest sunset on Dec 8, 2026 (4:19 to 4:21 pm across Dec 3 to Dec 17), and we compute Dec 8 at 4:20 pm for O’Hare’s coordinates. Other cities were not individually verified against an outside source, so treat times as accurate to about a minute. Re-running the calculation for 2025–2029 changed the earliest-sunset clock time of Chicago, Miami and Seattle by less than a second and the date by at most a day.

Limits: elevation, local terrain, buildings and weather are ignored; times describe a flat sea-level horizon. Do not use for navigation, aviation, legal deadlines or religious observance; use the official U.S. Naval Observatory tables.