I made a 3D solar system path visualizer that takes data from JPL's Horizon Systems and traces the path of planets and moons. You can chose to center the perspective on any body to see the path of the surrounding planets and moons from that observation point. Venus' orbit especially make a nice star pattern when the perspective is centered on the earth. Since this is from actual ephemeris data, you can see all the nuances and subtleties of the orbits. Speeding up the moon's path around the earth, for instance, reveals the irregularity over time. I'm new to astronomy. If anyone here is an armature or professional astronomer, I'd love to hear about resources or interesting topics. One day, I would love to make an astronomical clock for a smart watch, and am curious about cultural calendars and holidays from around the world. https://observablehq.com/d/8b01545347057429

Very nice and fun to play with! My only suggestion is to scale the length input by the average circumference (so it is in units of revolutions) and ask the user for the number of points per revolution (rather than the total number of points). I am a professional astronomer, but you have already discovered the gold standard (JPL Horizon) for solar system calculations that I use in my research.

Thanks for the feedback @David Kirkby! Points per revolution is a great idea I'll just need to figure how that would work for the epitrochoid orbits when centered at a secondary body. Since you are an astronomer, is there any feature you would want for an astronomical clock smart watch app?

For the purposes of planning observations, sun and moon ephemerides for the upcoming / current night are probably the most useful. Specifically, the times when the sun hits some angle below the horizon (in the range 10-20°, depending on the type of observation), and the times of moon rise/set together with the moon's illuminated fraction.