w / 2; cy = ch / 2;
                // 动态计算 9 条轨道等间距
                const maxOrbit = Math.min(cw, ch) * 0.45;
                const spacing = maxOrbit / 9;
                radii = [0];
                for (let i = 1; i < planets.length; i++) radii.push(spacing * i);

                orbitCanvas = document.createElement('canvas');
                orbitCanvas.width = cw; orbitCanvas.height = ch;
                orbitCtx = orbitCanvas.getContext('2d');
                orbitCtx.clearRect(0,