CalSky The graph labeled "Meteogram" tells you if the sky will be clear (top bar; black and blue is good, white is cloudy), the size of the seeing disk (points and diamonds under the top bar), the temperature (red line), the Moon (yellow line), among other things. Put the cursor on it for a description. Keep in mind that you have to set the geolocation on the upper right yellow box. Click on whatever the default location is (Tucson, usually), then type "Cerro Tololo, Chile", and then click on the Tololo location on the map. After that, it will ask you if you want to setup an account and other things. You can do that, or just ignore it and click "OK" at the bottom of the page. After that, the page with the info for Cerro Tololo should appear.