Ls vs. Julian Dates vs. Gregorian Dates

KRC works in J2000 dates (Time from Jan 1 noon,2000 UT) = Julian date 2451545.0

Step 1: Generate Ephemerids

Go to https://ssd.jpl.nasa.gov/horizons.cgi and use the following template:

Ephemeris Type [change] : OBSERVER

Target Body [change] : Mars [499]

Observer Location [change] : Solar System Barycenter (SSB) [500@0]

Time Span [change] : Start=1990-01-01, Stop=2040-01-01, Step=1 d

Table Settings [change] : QUANTITIES=14,18; date/time format=BOTH; angle format=DEG; output units=KM-D; range units=KM

Display/Output [change] : default (formatted HTML)

>>Generate Ephemeris<<

For satellites, use the parent body as the target body (Europa=> Jupiter for example) 1990-2040 is only adequate for body as far as Jupiter; for other bodies further away, expand this time window by multiple decades/centuries.

Step 2: Create Data File

Copy output table in text file on ~/Desktop/ (only copy the ephemerid data, not the headers or footers generated by Horizon)

Name file JPL_Horizon.txt

Step 3: Processing and Formatting

Run these lines in Davinci:

 Table               = read_lines("~/Desktop/JPL_Horizon.txt")
 Length              = length(Table)
 Date_Greg           = Table[:12,,1]
 Date_JD             = Table[20:28,,1]
 ObsSub_LAT          = atod(Table[53:60,,1])
 hEcl_Lon            = atod(Table[64:71,,1])
 BUFFER              = double(cat(0.,0.,axis=x))
 for(i=1;i<=Length-1;i+=1){
   if((ObsSub_LAT[1,i,1] < 0.)&&(ObsSub_LAT[1,i+1,1] > 0.)){
     Line   = cat(ObsSub_LAT[1,i:i+1,1],hEcl_Lon[1,i:i+1,1],axis=x)
     BUFFER = cat(BUFFER,Line,axis=y)
   }
 }
 DELTA_Ls            = fit(y=BUFFER[2,2:,1],x=BUFFER[1,2:,1],"linear",plot=1)[1,1,1]
 Ls                  = float(hEcl_Lon - DELTA_Ls)
 Ls[where Ls < 0.]   = Ls + 360.
 Ls[where Ls > 360.] = Ls - 360.
 Ls_2                = Ls[1,1,1] + ""
 for(i=2;i<=Length;i+=1){
   Ls_2 = cat(Ls_2,Ls[1,i,1]+"",axis=y)
 }
 OUT                 = Date_Greg + " " + Date_JD + " " + Ls_2
 write(OUT,"~/Desktop/BODY_Ls_Date.ascii",ascii,force=1)

The content of BODY_Ls_Date.ascii should now look like this:

1990-Jan-01 2447892.5 320.3994
1990-Jan-02 2447893.5 321.2871
1990-Jan-03 2447894.5 322.1805
1990-Jan-04 2447895.5 323.0793
1990-Jan-05 2447896.5 323.9838
1990-Jan-06 2447897.5 324.894
1990-Jan-07 2447898.5 325.8099
1990-Jan-08 2447899.5 326.7318
1990-Jan-09 2447900.5 327.6592
1990-Jan-10 2447901.5 328.5927
etc.

Step 4: Move File

Rename the file with the name of the body. For example Bennu_Ls_Date.ascii, Europa_Ls_Date.ascii, Mars_Ls_Date.ascii, Moon_Ls_Date.ascii etc.

Move the file to ‎⁨~/Applications/davinci⁩/Contents/⁨Resources/library/script_files/krc_support/porb_defaults⁩/

Step 5: Usage

For bodies associated with a BODY_Ls.ascii files, seasons can now be defined as Ls (ls), Julian Date (JD), and Gregorian Date (GD):

 OUT = krc(body="Moon",lat=25.,ls=90.)

For a specific Gregorian Date, GD (currently ranging from 1990-Jan-01 to 2040-Jan-01), the format is ????-Mmm-DD, with Mmm:Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec;

 OUT = krc(body="Moon",lat=12.,GD="2010-Jan-05")

or a specific Julian Date JD:

 OUT = krc(body="Moon",lat=12.,JD=2455201)