Re: explanation of aparent motion for comets in STRINGS.DAT

jarisuomela Dec 24, 2014

Hi Bernd,

I googeled with your setting string as search frase and easily found the below information on Project Pluto site.

Asteroid/comet rates of motion: The rate of motion of an asteroid or comet has long been given in "more info", expressed as a speed and position angle. In response to an inquiry on the Guide user list, they are now also given as rates in RA and declination. By default, both rates are given in degrees/day, but I realize that some people will want assorted other rates. To do this, you can edit the file strings.dat and look near the bottom for this line:
1,1:RMotion is %.2lf ^degree^s/day in RA, %.2lf ^degree^s/day in dec\n

The "1,1:R" tells Guide to multiply the rates in RA and dec by 1 and 1 (i.e., not scale them at all). If you wanted rates in arcseconds per day and arcminutes/day, you would revise that line to read:

3600,60:RMotion is %.0lf ^arcsecond^s/day in RA, %.1lf ^arcminute^s/day in dec\n

Units can be set on each axis. By changing the ":(space)" to ":R", you can switch the RA to be in time units rather than straight angular units. Mix-and-match all this, and you can get combinations such as:

15,60: Motion is %.1lf ^RA minute^s/day in RA, %.0lf ^arcminute^s/day in dec\n
.625,2.5: Motion is %.2lf ^RA minute^s/hour in RA, %.2lf ^arcminute^s/hour in dec\n
.625,2.5: Motion is %.2lf ^RA second^s/minute in RA, %.2lf ^arcsecond^s/minute in dec\n
37.5,150: Motion is %.1lf ^RA second^s/hour in RA, %.0lf ^arcsecond^s/hour in dec\n

The above gives positive RA motion to the west. To reverse this, negate the RA multiplier; for example, the first line would become

-15,60: Motion is %.1lf ^RA minute^s/day in RA, %.0lf ^arcminute^s/day in dec\n

Kind regards,