Sunrise and sunset times, by city

Sunrise and sunset come from the apparent position of the Sun (Meeus’s series, the same one behind the NOAA solar calculator), solved for the instant when the centre of the Sun crosses an altitude of −0.833°, which puts the upper limb on the horizon with the standard 34′ of refraction. That is the USNO convention. Twilights use −6°, −12° and −18°. Where the Sun never crosses those altitudes the page says there is no sunrise or sunset instead of inventing a time. Checked against the USNO for several cities, including a polar one: largest difference one minute.