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Additional Slide [not shown in class] …Sundial will show “real” Local Solar Time ….Correction to Mean Solar Time given by the “equation of time”… [Image Credit: HartRAO] ….number of minutes to be subtracted from Local Solar Time to obtain Mean Solar Time Note Tilt: 6 month period Orbit: 12 month period Ian M. George PHYS 304 (2011 Fall) Meeting 04
Additional Slide [not shown in class] is actually not that easy in detail …. - Earth’s rotation rate is slowly decreasing - Precession of the spin axis - plus additional wobbling due to “Nutation” (caused by precession of Moon’s orbit around the ecliptic every 18.6 yrs) - and other effects Hence even Sidereal Time is not constant with “time” due to all these effects but corrections can be calculated & applied Mean Sidereal Time (“UT0” & variations) often used eg. “Greenwich Mean Sidereal Time” or “Universal Time” Ian M. George PHYS 304 (2011 Fall) Meeting 04
Page 1 and 2: Meeting #4 PHYS 304 Meeting 04
Page 3 and 4: [Image Credits: Stellarium] … rig
Page 5 and 6: …relationship between systems can
Page 7 and 8: … again its usually best to choos
Page 9 and 10: Origin: Sun “Special Direction #1
Page 11 and 12: … which corrections are really ne
Page 13 and 14: Tilt angle stays (approx) constant
Page 15 and 16: For the last few years… The preci
Page 17 and 18: … for ground-based observations
Page 19 and 20: A final problem for ground-based ob
Page 21 and 22: … even spin axis wobbles (v.sligh
Page 23 and 24: there are 24 hours in a “Day”,
Page 25 and 26: Additional Slide [not shown in clas
Page 27 and 28: Solar Day is longer than Sidereal D
Page 29: ut Solar Time is actually a bit tri

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