Time System

Longitude and UTC Relation

Example 1				Example 2
New York	West	← Greenwich →	East	Beijing
74 W	West	← Longitude [deg] →	East	116 E
-74	Negtive	← Longitude [deg] →	Positive	+116
UTC-5 or UTC-4	`-`	← UTC →	`+`	UTC+8

Given $t_{UTC}$, local mean time $t_{LMT} = t_{UTC} + \frac{lon}{360} \times 24hr$.

For verification, New York is at (40.730610 N, 73.935242 W) or (+40.730610, -73.935242). New York timezone is Eastern Standard Time (EST) UTC-5 in winter, and Eastern Daylight Time (EDT) UTC-4 in summer. The calculation based on longitude is $t_{LMT} = t_{UTC} + \frac{-74}{360} \times 24hr \approx t_{UTC} - 4.9hr$, which is consistant with UTC-5.