爱华网UTCUTC 是 Coordinated Universal Time的缩写，译为中文为“世界标准时间”，直译的话，可译为“协调通用时间”或“协调世界时间”。目前来说也就是指 GMT时间。为什么说目前就是指 GMT 时间呢？因为本初子午线（子午线即经线，本初子午线即 0度经线）其实穿过的是沙特阿拉伯西边的麦加，而不是英国的格林威治。当时英国皇家学会暂时确定格林威治为本初子午线的穿过点﹐加之英国正是兴旺发达时期，全世界就将错就错，用到现在。说不定哪天改为麦加时间为标准时间也不是没有可能。所以我们一般使用UTC，而不是 GMT。Coordinated Universal Time (UTC), also referred to as GreenwichMean Time (GMT), Universal Time (UT), or "Zulu" is an internationaltime scale used in astronomical and aviation publications, weatherproducts, and other documents. UTC uses 24-hour (military) timenotation and is based on the local standard time on the 0°longitude meridian which runs through Greenwich, England. Midnightin Greenwich corresponds to 00:00 UTC, noon corresponds to 12:00UTC, and so on.PDTPDT 是 Pacific Daylight Time 的缩写，译为中文为“太平洋夏令时间”，比 UTC 时间晚 7小时。
PDT is 7 hours behind of Coordinated Universal Time(UTC)Notethat PDT is adaylightsaving time/summer timezone.It is generally only used during the summer in the places listedbelow, during the winterPSTisused instead
US states using PDT in the summer andPSTduringwinter
The following table provides a convenient way to convert betweenUTC and U.S. and Canadian time zones1.
| PST | PDT | MST | MDT | CST | CDT | EST | EDT | UTC |
|---|---|---|---|---|---|---|---|---|
| 4 p.m. | 5 p.m. | 5 p.m. | 6 p.m. | 6 p.m. | 7 p.m. | 7 p.m. | 8 p.m. | 00:00 |
| 5 p.m. | 6 p.m. | 6 p.m. | 7 p.m. | 7 p.m. | 8 p.m. | 8 p.m. | 9 p.m. | 01:00 |
| 6 p.m. | 7 p.m. | 7 p.m. | 8 p.m. | 8 p.m. | 9 p.m. | 9 p.m. | 10 p.m. | 02:00 |
| 7 p.m. | 8 p.m. | 8 p.m. | 9 p.m. | 9 p.m. | 10 p.m. | 10 p.m. | 11 p.m. | 03:00 |
| 8 p.m. | 9 p.m. | 9 p.m. | 10 p.m. | 10 p.m. | 11 p.m. | 11 p.m. | Midnight | 04:00 |
| 9 p.m. | 10 p.m. | 10 p.m. | 11 p.m. | 11 p.m. | Midnight | Midnight | 1 a.m. | 05:00 |
| 10 p.m. | 11 p.m. | 11 p.m. | Midnight | Midnight | 1 a.m. | 1 a.m. | 2 a.m. | 06:00 |
| 11 p.m. | Midnight | Midnight | 1 a.m. | 1 a.m. | 2 a.m. | 2 a.m. | 3 a.m. | 07:00 |
| Midnight | 1 a.m. | 1 a.m. | 2 a.m. | 2 a.m. | 3 a.m. | 3 a.m. | 4 a.m. | 08:00 |
| 1 a.m. | 2 a.m. | 2 a.m. | 3 a.m. | 3 a.m. | 4 a.m. | 4 a.m. | 5 a.m. | 09:00 |
| 2 a.m. | 3 a.m. | 3 a.m. | 4 a.m. | 4 a.m. | 5 a.m. | 5 a.m. | 6 a.m. | 10:00 |
| 3 a.m. | 4 a.m. | 4 a.m. | 5 a.m. | 5 a.m. | 6 a.m. | 6 a.m. | 7 a.m. | 11:00 |
| 4 a.m. | 5 a.m. | 5 a.m. | 6 a.m. | 6 a.m. | 7 a.m. | 7 a.m. | 8 a.m. | 12:00 |
| 5 a.m. | 6 a.m. | 6 a.m. | 7 a.m. | 7 a.m. | 8 a.m. | 8 a.m. | 9 a.m. | 13:00 |
| 6 a.m. | 7 a.m. | 7 a.m. | 8 a.m. | 8 a.m. | 9 a.m. | 9 a.m. | 10 a.m. | 14:00 |
| 7 a.m. | 8 a.m. | 8 a.m. | 9 a.m. | 9 a.m. | 10 a.m. | 10 a.m. | 11 a.m. | 15:00 |
| 8 a.m. | 9 a.m. | 9 a.m. | 10 a.m. | 10 a.m. | 11 a.m. | 11 a.m. | Noon | 16:00 |
| 9 a.m. | 10 a.m. | 10 a.m. | 11 a.m. | 11 a.m. | Noon | Noon | 1 p.m. | 17:00 |
| 10 a.m. | 11 a.m. | 11 a.m. | Noon | Noon | 1 p.m. | 1 p.m. | 2 p.m. | 18:00 |
| 11 a.m. | Noon | Noon | 1 p.m. | 1 p.m. | 2 p.m. | 2 p.m. | 3 p.m. | 19:00 |
| Noon | 1 p.m. | 1 p.m. | 2 p.m. | 2 p.m. | 3 p.m. | 3 p.m. | 4 p.m. | 20:00 |
| 1 p.m. | 2 p.m. | 2 p.m. | 3 p.m. | 3 p.m. | 4 p.m. | 4 p.m. | 5 p.m. | 21:00 |
| 2 p.m. | 3 p.m. | 3 p.m. | 4 p.m. | 4 p.m. | 5 p.m. | 5 p.m. | 6 p.m. | 22:00 |
| 3 p.m. | 4 p.m. | 4 p.m. | 5 p.m. | 5 p.m. | 6 p.m. | 6 p.m. | 7 p.m. | 23:00 |
To illustrate how to convert UTC to local time, assume that anevent will occur on Wednesday at 06:00 UTC and you want to convertthis to PDT. Using the UTC conversion table, you can see that 06:00UTC Wednesday translates to 11 p.m. PDT Tuesday.
其实除了 PDT 时间，北美地区还有很多时间：
美国夏季始于每年4月的第1个周日，止于每年10月的最后一个周日。夏令时比正常时间早一小时，与PDT时间相对应的是PST, Pacific Standard Time 。 夏时制结束后就是PSTPST
PST是太平洋标准时间（西八区），与北京时间（东八区）时差-16个小时，也就是北京时间减去16就是PST时间。而PDT比PST早1个小时，就是说PDT与北京时间时差为-15小时
夏令时Daylight Saving Time 或 Daylight Time。美国和加拿大原本于每年10月的最后一个星期日凌晨2时起实施冬令时间；4月的第一个星期日凌晨2时起，恢复夏令时间。
但是根据美国国会最新通过的能源法案，为加强日光节约，自2007年起延长夏令时间，开始日期从每年4月的第一个星期日，提前到3月的第二个星期日，结束日期从每年10月的最后一个星期日，延后到11月的第一个星期日。换言之，冬令时间将缩短约一个月。之所以安排在周日，是为了便于生活的调整不至于受到较大的影响。
