A year of daylight

Questions

FAQ

How accurate are the sunrise / sunset times?

Within roughly one minute for cities in mid-latitudes (most of the populated world). Accuracy degrades at extreme latitudes — above the Arctic Circle, the rapidly-changing sun angle can put real values 5-10 minutes off our approximation. For pinpoint accuracy at high latitudes, use a national meteorological service rather than this curve.

Why does Reykjavík show 0 hours in deep winter?

Because at 64 degrees north the sun barely clears the horizon for a few hours in late December, and our refraction model rounds those marginal cases down. In reality Reykjavík does see roughly 4 hours of dim daylight on the shortest day. The curve is correct in shape (massive seasonal swing) but conservative in the exact minimum.

Are the times in local time or UTC?

Daylight totals (in minutes) are timezone-invariant — they're just sunset minus sunrise. The displayed daily totals are computed for each calendar date in the city's civil time, so DST shifts don't cause artefacts in the curve.

Does this account for elevation or atmospheric refraction?

It accounts for standard atmospheric refraction (the reason the sun appears 0.833° above the geometric horizon at sunrise). It does not account for elevation or terrain; if you're at the bottom of a deep valley your effective sunrise is later than what's shown. For mountain or maritime calculations, use a dedicated solar-position library.