How it works

Sunset and twilight

• Sunset is when the top edge of the Sun touches a flat horizon, with normal air bending the light a little (refraction). Sunrise is the same in the morning.
• Civil twilight is while the Sun is up to 6° below the horizon: still light enough to see outside. We call its end “dark” and “light until”.
• Nautical twilight is 6–12° below: dusk; streetlights on, most stars not out yet. Its end is “fully dark”.

These are the same definitions the U.S. Naval Observatory uses (Sun and Moon Data for One Day (opens in a new tab)). Times are rounded to the nearest minute, as the Observatory does.

What 5 pm looks like

We work out how high the Sun is at exactly 5:00 pm on your clock, and describe it in plain words:

• Sun above the horizon: “the sun is still up”.
• 0 to 6° below: “the sun has just set: it's twilight”.
• 6 to 12° below: “it's dusk, nearly dark”.
• More than 12° below: “it's dark”.

The day band on the tool uses the same Sun height, minute by minute, to colour the sky.

Accuracy: checked against the U.S. Naval Observatory

Computed We compute with Astronomy Engine 2.1.19 (MIT, by Don Cross). For 10 ZIP codes on 4 dates, we compared sunrise, sunset, civil dawn and civil dusk with the Naval Observatory: all 160 times match to the minute (largest difference: 0 minutes). Across every day of 2026 and 2027, 21,844 comparisons from the Observatory's full-year tables are all within 1 minute, and 21,208 are exact.

Sunset in each ZIP's own clock time. The Observatory's values are identical on every date shown.

Clock change rules

Federal law sets daylight saving time from 2:00 a.m. on the second Sunday of March to 2:00 a.m. on the first Sunday of November (15 U.S.C. §260a (opens in a new tab)). A state may exempt itself and stay on standard time. In 2026 that means clocks fall back on Sunday, Nov 1 at 2:00 a.m. (NIST (opens in a new tab)). The next changes: spring forward Sun, Mar 14, 2027, and fall back Sun, Nov 7, 2027.

Places that don't change clocks: Hawaii, American Samoa, Guam, Puerto Rico, the U.S. Virgin Islands, the Northern Mariana Islands and Arizona (except the Navajo Nation).

We never hard-code these dates per place: your browser's own time-zone database (the IANA tz database) knows each zone's rules, and we read every clock time through it.

Arizona, the Navajo Nation and time-zone lines

Arizona stays on standard time all year. The Navajo Nation, which reaches into Arizona, New Mexico and Utah, does change clocks. The Hopi Reservation, surrounded by the Navajo Nation, does not (IANA tz database (opens in a new tab)).

For every Arizona ZIP we used Census data to decide which side it's on, and we ask “Do your clocks change on Nov 1?” so you can confirm. Eight ZIPs cross the Navajo Nation line; for those we show a warning and let you pick.

Elsewhere, a ZIP right next to a time-zone line (for example in the Florida panhandle, Tennessee, Kentucky, Indiana, the Dakotas, Nebraska, Kansas, Texas, Oregon or Idaho) can land in the wrong zone. Your time zone is always shown next to your result: if it's not the one on your clocks, press Change and pick yours. Whether a place uses daylight saving time is right for every ZIP.

Privacy

The ZIP lookup happens in your browser. The page loads a small file of ZIP locations named after the first 3 digits of your ZIP from this same website, so your full ZIP is never sent anywhere. All the astronomy runs on your device. There are no inputs in the web address, and your ZIP is never sent to analytics or put in the share picture. If you want, we remember your place on this device only; Forget this place erases it.

We use Google Analytics to count visits and which buttons get pressed (like “Share picture”), and whether a result used daylight saving time or not. Never your ZIP, city, time zone or times. See the privacy policy (opens in a new tab).

Limits

Sources