How to calculate Ls

[cristiapi]

Ls is the solar longitude as well explained here.

I calculate Ls using library functions or algorithms like this, but I'd like to know a "general" procedure valid for any celestial body.

I can calculate the position and the velocity of the body (and hence I can calculate any orbital element); please, could somebody tell me how to calculate Ls?

 

[Keithth G]

What are you trying to do here? Calculate the apparent position of the Sun in the sky from an arbitrary point on an arbitrary planet/moon?

 

[cristiapi]

Calculate the longitude of the Sun as seen from the center of any celestial body along the Sun path (as seen from the body).

Ls is mainly used to determine the season on a particular celestial body. Quoting the link: "The way that scientists mark the time of Mars year is to use solar longitude, abbreviated Ls (read "ell sub ess"). Ls is 0° at the vernal equinox (beginning of northern spring), 90° at summer solstice, 180° at autumnal equinox, and 270° at winter solstice.".

In the meanwhile, I found that Ls= true_anomaly + Ls_perigee, which seems in good agreement with the exact values obtained from the library (SPICE) function (error < 1°).