Announcements Homework set 1 is due today Homework set 2:
Chapter 2 # 43 & 45 plus supplemental problems Use Exam Formula
Sheet as you do the homework to familiarize yourself with where
things are on it. Projectsee website Exam 1 is two weeks away. Will
look a lot like the homeworkall problems.
Slide 2
Terrestrial Coordinates Longitude is measured CCW (+) or CW (-)
around from Greenwich England Latitude is measured North or South
of the equator Both are measured in degrees, minutes and
seconds
Slide 3
Celestial Coordinates The angle between the celestial equator
and the ecliptic is 23.5 Right Ascension (RA) is measured CCW from
the Vernal Equinox and is in hours, minutes and seconds Declination
(Dec) is measured above (+) or below (-) the celestial equator and
is in degrees, minutes and seconds See Appendix A6 for more on
celestial coordinates
Slide 4
Finding the CE and NCP at your latitude Altitude of NCP above
due north horizon along the meridian (the North Point) is just ,
your latitude (+ for north, - for south) Altitude of the celestial
equator above due south horizon along the meridian (the South
Point) is 90-
Slide 5
Sidereal Time Sidereal 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 seconds.
However, one sidereal day is 24 sidereal hours
Slide 6
Calculating Sidereal Time Step 1 First: convert standard time
to universal time in military time format (i.e. 7:15pm UT = 1915
UT) For Central Standard Time UT = CST + 6 hours For Central
Daylight Time UT = CDT + 5 hours If result is greater than 24 hrs,
subtract 24 and add 1 to the date. Put into decimal format (i.e.
1915 UT = 19.25 UT)
Slide 7
Calculating Sidereal Time Step 2 Calculate 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 dont own a
current Astronomical Almanac, use the following formula to find GST
GST = G + 0.0657098245xN + 1.00273791xUT where G = GST at 0 hrs on
zeroth day of that year N = number of days since the beginning of
the year
Slide 8
Calculating Sidereal Time Step 4 Correct for local longitude
Divide 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 )
Slide 9
Julian Date Useful for calculating time interval between two
dates. Julian dates start at noon UT The Julian Date (JD) is the
number of days since January 1, 4713 BCE Where N is the day number
and L is the number of leap years since 2000
Slide 10
Examples Find the current sidereal time (9:45am) and the
current Julian date First, find current sidereal time (LST) then
find Julian date
Slide 11
Solution for LST Using the formula for LST on the formula
sheet, we will need to know the time (9:45am), G for 2015, N for
February 5 and the longitude of Clarksville, TN. In 24 hour decimal
format 9:45am = 09:45 = 9.75 The USNO location for Clarksville, TN
is 8722 = 87.37 From the formula sheet G 2015 = 6.62294 From the
formula sheet N February 5 = 36
Slide 12
Final value for LST You can check the value in Stellarium by
determining the Right Ascension of a star on the meridian at 9:45am
on February 5, 2015 A word about significant figures and time
Slide 13
Solution for Julian Date From the equation for JD on the
formula sheet we need N for February 5 and L for 2015 N = 36 L = 3
(2004, 2008 & 2012 were the three leap years) Plugging in the
numbers This can be checked on the USNO Data Services page using
their Julian Date Conversion calculator (Use Sunrise/Sunset
Moonrise/Moonset Times link on www.apsu.edu/astronomy)