= now - lastTime;
                lastTime = now;
                fps = dt > 0 ? 1000 / dt : 0;
                sumFPS += fps;
                frameCount++;
                avgFPS = sumFPS / frameCount;
                const elapsed = (now - startTime) / 1000;   // s
                const earthDay = elapsed * 10;             // 地球日

                // 请求下一帧的位置
                worker.postMessage({ time: elapsed, radii: radii, speeds: speeds, centerX: cx, centerY: cy });

               