A nice script for rotating planets (according to the Spelljammer campaign guide) in Roll20.

planetaryRotation.js

var SplenectomY = SplenectomY || {};

SplenectomY.planets = SplenectomY.planets || {};

//////////////////////////////////////////////////
//HERES THE CONFIG. SAVE AND RESTART UPON CHANGING.
SplenectomY.planets.clockwise = false;
//////////////////////////////////////////////////
//////////////////////////////////////////////////



on('ready',function() {

    SplenectomY.planets = findObjs({
        _type: "graphic",
        gmnotes: "isPlanet",
    });
});

on("chat:message", function(msg) {
    
    if(msg.type == "api" && msg.content.indexOf("!protate ") !== -1) {
        var days = (msg.content.replace("!protate ", ""));
        
        _.each(SplenectomY.planets, function(obj) {
            var mult = 0;
            if(obj.get("name") == "Anadia") {mult = 12;};
            if(obj.get("name") == "Coliar") {mult = 1.5;};
            if(obj.get("name") == "Toril") {mult = 360/365;};
            if(obj.get("name") == "Karpri") {mult = 360/650;};
            if(obj.get("name") == "Chandos") {mult = 360/2010;};
            if(obj.get("name") == "Glyth") {mult = 360/10800;};
            if(obj.get("name") == "Garden") {mult = 360/30660;};
            if(obj.get("name") == "HCatha") {mult = 360/60120;};
            var angle = obj.get("rotation");
            if (SplenectomY.planets.clockwise == true) {
                var newangle = angle + (days * mult);
            } else {
                var newangle = angle - (days * mult);
            };
            
            obj.set("rotation", newangle);
        });
    };
});