Questions & Answers about Solar Time Zones

Contents

• How does one differentiate between hour and 15-minute Solar Time Zones with the same UTC offset?
• What is the difference between UTC offset time zones, military time, nautical time and Solar time zones?

How does one differentiate between hour and 15-minute Solar Time Zones with the same UTC offset?

The difference is the narrow time zones have 2 more digits in their names, for the number of minutes offset. When the minutes are 00, the narrow time zone has the same offset as the hour-wide zone, though in one quarter the area.

For every hour-based solar time zone, there are four 15-minute zones overlain by their area. For example, Seattle WA, Portland OR and San Jose CA are in the West08 hour-wide time zone, and the West0815 15-minute-wide time zone. West0800 includes Sacramento CA, Reno NV and Bend OR which are all also in West08, but not in West0815.

One quirk is the narrow time zones with 30 minute offsets (xx:30) are centered on a boundary between hour-based time zones. So their overlap is half with one on their east half and half with the adjacent one on their west half.

What is the difference between UTC offset time zones, military time, nautical time and Solar time zones?

UTC offset time zones, such as UTC-08:00, differ from Solar time zones, such as West08 in whether or not a geographical boundary is defined. Both are centered around 120° West longitude.

• UTC-08:00 is a reference to anywhere that observes an 8 hour offset behind UTC, without specifying geographical boundaries. Regionally-legislated time zones can and often do differ in boundaries from the ideal longitude center and width.
• The Solar time zone West08 is defined not only by the 8 hours offset behind UTC, but also by the geographical boundaries. The time zone’s boundary is between 112.5°W and 127.5°W longitude (120°W ±7.5°). Solar time zones are also defined as only between ±80° latitude, deferring to UTC, or equivalent East00 if preferred, in the vicinity of the North and South Poles.
• The military time zone “Uniform” is equivalent to West08 in that it specifies a clock offset and the same longitude boundaries. The definition of military time does not include an 80° cut-out for the polar regions.
• Nautical time is used by ships at sea with the same longitude boundaries as military time and solar time. Ship captains typically decide on clock settings each night for the longitudes spanned in the following day’s planned route.