Sunrise and sunset depend on just three things: your latitude, the date (which sets how the Earth is tilted toward the sun), and your longitude (which sets your clock relative to the sun). This tool computes the sun's declination and the hour angle at which it crosses the horizon, then converts to your city's local time — daylight saving included. No internet lookup, no data feed; it's pure astronomy.
On the June solstice, London gets about 16 hours 39 minutes of daylight — sunrise near 4:43 am, sunset near 9:21 pm. Six months later at the December solstice it's under 8 hours. The equator barely changes: about 12 hours all year.
The higher your latitude, the more extreme the swing. Past the Arctic or Antarctic Circle it becomes total — the sun never sets in midsummer, and never rises in midwinter.
The period when the sun is just below the horizon (up to 6° down) — dim but still light enough to see outside without artificial lighting. It's why it's bright well before sunrise and after sunset.
Because land and sea take weeks to warm up. Peak daylight is the solstice, but peak temperature lags by a month or two — the same reason the hottest part of the day is after noon, not at it.
Within about a minute for a flat sea-level horizon. Mountains, tall buildings, and altitude can shift the real moment you see the sun by several minutes either way.
Clocks run at a steady pace; the sun doesn't, quite — the Earth's tilt and elliptical orbit make solar noon wander by up to ~16 minutes over the year (the "equation of time"), plus an offset for your longitude within your time zone.