Why sunrise times differ across a single time zone

Two cities share a time zone, so their clocks read the same. The sun does not care. In one the sky is bright at seven in the morning and in the other it is still dark, and the reason is that a time zone is an administrative band while sunrise is set by where you are on the turning Earth.

Longitude sets the sun, politics sets the clock

The Earth turns 15 degrees of longitude in an hour, so a place 15 degrees west of you sees the sun rise about an hour later in solar terms. Time zones are drawn in bands roughly that wide, but the boundaries follow borders, provinces and convenience rather than meridians, and some zones are far wider than 15 degrees. Inside a wide zone, the eastern edge gets early sunrises by the clock and the western edge gets late ones.

The extreme case is a country that runs one clock across several natural zones. The far west of such a country can see the sun rise well after what the clock calls morning, with the whole daily rhythm shifted to match.

Latitude sets the swing

Longitude decides when the sun rises. Latitude decides how much that time moves through the year. Near the equator sunrise barely shifts between January and July. In northern Europe or southern Chile it moves by hours, and above the polar circles the sun does not rise at all for part of the year. Two cities in the same zone at very different latitudes will therefore agree in one season and diverge sharply in another.

Daylight saving moves the clock, not the sun

A clock change of one hour shifts every sunrise time by an hour overnight, which is the entire point of the exercise: it moves the working day relative to the daylight rather than creating any. The sun itself does exactly what it did the day before.

Why the tables are worth checking

People planning anything outdoors, from photography to construction to a morning run, tend to carry a rough sunrise time in their heads that came from somewhere else, often a nearby city that shares their zone. Across a wide zone that estimate can be half an hour or more out, which is the difference between a good light and a missed one.

The sunrise and sunset tool computes the times for a specific place rather than for a zone, so it accounts for the longitude and latitude that actually decide the answer. If two cities in your zone differ by more than you expect, the map is the explanation.