Case study US
US lower-48 time zones
From the eastern to the western United States
US time zones approximate the change in solar time across longitude, while their boundaries accommodate communities and administration. The day–night boundary follows Earth’s geometry.
Preparing map style and visible tiles…
Location: 39.80°, -98.60°
Places farther west reach local solar noon later because Earth rotates eastward. A difference of 15 degrees in longitude corresponds to about one hour of solar time. Civil time zones group places under a common clock rather than changing continuously with longitude.
Use the rotation model to follow two locations, then compare that smooth progression with a time-zone map. Include the date when checking an actual clock difference, because daylight-saving rules can affect the result.
Exam-style question
If solar noon has just reached New York, about how long until solar noon in a place 45° of longitude further west?
Teacher hint: A 45-degree longitude difference corresponds to about three hours of local solar time. Civil clock differences depend on zone rules.
Sources
- NIST / USNO