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Announcements. No lab after lecture tonight because of the 1 st Quarter night last Tuesday Homework: Chapter 2 # 2, 3, 4, 5, 7 & 8 Binoculars are available for check-out. I have six on campus and another eight out at the Farm.
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Announcements
  • No lab after lecture tonight because of the 1st Quarter night last Tuesday
  • Homework: Chapter 2 # 2, 3, 4, 5,7 & 8
  • Binoculars are available for check-out. I have six on campus and another eight out at the Farm.
  • Telescopes can also be checked out for a weekend. They must be returned Monday.
  • Don’t forget the Lunar Observations lab
  • TimeKeeping time by the Sun isn’t very accurateThe Equation of TimeSince solar time varies by location, we use standard timeEach zone is 15° wide with allowance for political boundaries The Earth’s rotation rate isn’t constantTerrestrial Dynamical Time corrects for the changes in Earth’s rotation rateSidereal TimeSidereal time is the time with respect to the background stars. One sidereal day is the true rotational period of the Earth. Uncorrected, it is 23 hours 56 minutes 4.091 secondsCalculating Sidereal TimeStep 1First: convert standard time to universal timeFor Central Standard Time UT = CST + 6 hoursFor Central Daylight Time UT = CDT + 5 hoursIf result is greater than 24 hrs, subtract 24 and add 1 to the date.Calculating Sidereal TimeStep 2Determine the “solar interval” and convert to sidereal interval.The solar interval is simply the time since 0 hrs UTSolar to sidereal interval conversion: multiply by 1.00273791Calculating Sidereal TimeStep 3Calculate the Greenwich Sidereal Time (GST)Look up the sidereal time at 0 hrs Greenwich for the date and add the sidereal interval to it.If you don’t own a current Astronomical Almanac, use the following formula to find GSTGST = G + 0.0657098245N + 1.00273791UTwhereG = GST at 0 hrs on “zeroth day” of that year (see Appendix 3 of textbook)N = number of days since the beginning of the year Calculating Sidereal TimeStep 4Correct for local longitudeDivide local longitude by 15° and add (if east of Greenwich) or subtract (if west of Greenwich) to GST to get Local Sidereal Time (LST)LST = GST ± (Longitude/15°)Julian DateUseful for calculating time interval between two dates. Julian dates start at noon UTThe Julian Date (JD) is the number of days since January 1, 4713 BCEJD = 2,451,544.5 + 365 x (Year – 2000) + N + LWhere N is the day number and L is the number of leap years since 2000The Julian CalendarInstituted around 46 B.C. 1 year = 365.25 daysYears evenly divisible by 4 have 366 days.All other years have 365The Tropical Year, sidereal year plus the effects of the Precession of the Equinox, is 365.242190 days so the Julian calendar “drifts”The Gregorian CalendarFirst instituted in 15821 year = 365.2425 daysYears evenly divisible by 4 have 366 days except century years. Only century years evenly divisible by 400 have 366 days. All other years (including century years not evenly divisible by 400) have 365 daysModified Gregorian Calendar(Never officially adopted) 1 year = 365.24225Years evenly divisible by 4000 are not leap years. Otherwise the same as the Gregorian Calendar
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