Su "liner StJStiCS Winter solstice
June El or 22 December 21 Of 22
Hgo n. 6-1 Hie effect of the earth’s till and rulaunD — ibout the sun.
Apparent solar time (Local solar time) is determined by a sundial (The sun’s position in the sky).
15° longitude —» I hour 1° longitude —» 4 min
Mean time (Standard time): GCT = Greenwich Civil Time (0° longitude)
Local Civil Time (LCT): Determined by longitude.
Local Stand Time: Through the center of a time zone
EST = Eastern Standard Time (75° W longitude)
CST = Central Standard Time (90° W longitude)
MST = Mountain Standard Time (105° W longitude)
PST = Pacific Standard Time (120° W longitude)
Equation of time is a factor of earth orbital velocity. Due to non-symmetry of earth’s orbit, earth’s rotational speed is irregular (T Table 6-1 or A Table 8).
Local solar time = Local standard time
+ Equation of time
+ 4 (Local standard time meridian — local longitude) [Minutes]
Local Solar Time (LST): Time measured by position of sun Daylight Saving Time (1 hr advance in summer)
Longitude of a PSU classroom is 78° W. Determine the local solar time at EST 12:00 noon on February 21.
EST is for longitude of 75° W. From T Table 6-1 or A Table 8, equation of time is about -14 minutes. Then
Local solar time = Local standard time + Equation of time
+ 4 (Local standard time meridian — local longitude)
= 12:00-0:14 + 0:4 (75-78)
= 11:34 am.
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