Time in San Juan, Puerto Rico
San Juan’s time zone: UTC-04:00 or AST
Daylight saving time (DST) changes in San Juan
Sunrise and sunset time for San Juan
Sunset: 5:49 PM
Day length: 11h 5m 28s
Solar noon: 12:16 PM
See the monthly sunrise, sunset, and twilight table for San Juan
San Juan, Puerto Rico
Time and time zones
The length of a solar day is determined by the time that it takes for the Earth to complete a full rotation around its axis and equals 24 hours. The Earth’s rotation on its axis leads to change between day and night. Another consequence of this rotation is the fact that while moving by 15° from West to East local solar time increases by an hour.
In everyday life people use official local time which almost always differs from solar time. All of the Earth’s surface is divided into time zones. All places within the same time zone observe the same time. Time zone boundaries usually follow country or administrative borders. Time difference between adjacent time zones normally equals one hour, though sometimes time in neighbouring time zones may differ by two or more hours. There are also cases when adjacent time zone difference equals 30 or 45 minutes.
For most countries the entire country’s territory lies within the same time zone. Countries whose territory stretches from West to East by a significant distance, such as Russia, USA, Canada, Brazil and some others, are usually divided into a few time zones. One notable exception is China where Beijing time serves as the official time all over the country.
Coordinated Universal Time or UTC is the reference point to determine time zone offsets. UTC corresponds to mean solar time on the Prime or Greenwich Meridian (0° longitude). Time zone offsets from UTC range from UTC-12:00 to UTC+14:00.
Almost all countries in Europe and North America as well as many other countries observe Daylight Saving Time (DST) and put their clocks an hour forward in the spring and an hour back in the autumn. In these countries time zone offsets from UTC change twice a year. Most countries do not observe DST though.