atmosphere: simulate Earth-Sun distance for solar irradiance

background.html

@@ -1891,6 +1891,7 @@ window.weatherThemes = {
             var _sunNow = sceneNow();
             var _sunPos = SunCalc.getPosition(_sunNow, SITE_LAT, SITE_LON);
             window.__currentSunAlt = _sunPos.altitude;
+            window.__currentSceneDate = _sunNow;
             window.__flightDow = _sunNow.getDay();
             // Unit vector towards the sun in world space. SunCalc azimuth
             // is measured from the south, positive towards the west, so the