2021-07-04, 03:45 AM
Horizons does each step calcs and creates new (osculating) elements prior to next step, so yes, takes into account the gravity of the perturbing objects. It is not a two-body calc as most of our software does (MegaStar, The Sky X, Stellarium). With really close small fast movers, we need to update elements rather often (each step) if we want good positions. There was a very old piece of software that did that called "Dance of the Planets". Doesn't run well on modern PCs. There are some online that you can create your own simulation as well as some modern software that will simulate gravity. Do a search for solar system gravity simulators. Nothing I've seen that can display/print tracks with such ease like SkyTools 4. You just need to stay close to the epoch of elements. And if done correctly, the positions in SkyTools completely agrees with Horizons. The most tricky part is determining when the best viewing window is for your location as these fast movers run the sky quickly. I'm still struggling with that a bit. Occasionally, the magnitude will be wildly off in the generated ephemeris (ST) - example - 2008 GO20 close on July 24, 12:13UT - big rock (92-210 meters) shows obvious difficulty, 5.2 mag but not shown on IA (most likely due to low altitude).