The Sun and the seasons
Day length, solar noon, twilight and the off-center clock: why the earliest sunset is not on the shortest day, and why the equinox is not twelve hours.
Sun and Seasons
5 guides filed under this heading
- Why the equinox gives twelve hours and seven minutes of daylight
Refraction lifts the Sun above the horizon and its disc has width, so the day runs long everywhere — by about seven minutes at the equator.
3 min read - The earliest sunset is ten days before the shortest day
At 40°N the Sun sets earliest around December 7 but the shortest day is December 22. Two separate effects pull sunrise and sunset apart.
3 min read - Solstice and equinox are not the same kind of event
One is a turning point in declination, the other a crossing. The difference explains why the seasons lag, and why the Sun is closest in January.
3 min read - The equation of time: why solar noon keeps missing 12:00
The Sun's clock runs fast in November and slow in February, by up to 16 minutes. The two causes are obliquity and orbital eccentricity.
3 min read - Twilight in three depths: civil, nautical and astronomical
The Sun 6°, 12° and 18° below the horizon mark three different kinds of darkness — and the time between them ranges from 20 minutes to none at all.
3 min read
Reference pages
Tables and lookups on the same filing, answered without reading around it
- Sunrise and sunset for sixteen cities, on any date
Sunrise, sunset, solar noon and day length for sixteen cities on any date, computed from the NOAA solar algorithm and shown in each city's own clock time.
Other topics on Meridian
Every guide on this site is filed under one of these
The Moon
Phase, rise, set, distance and the illusions in between — what the Moon actually does, computed for a place and a date rather than described.
Eclipses and meteor showers
Shadow geometry and dust: which dates are real, where you have to stand, and the difference between a rate on paper and a rate in the sky.
The night sky
Constellations, precession, what your latitude hides from you, and how much of it light pollution has already taken.