One very helpful tool in our observatory operations has been the Clear Sky Chart. This timely clock shows the conditions of sky clarity, haziness, moisture, wind, and temperature all in one handy plot. Skies are generally clear when both Cloud Cover and Transparency fields are dark blue to black in color for any given time. Time is the x-axis with a red vertical line showing midnight. Darkness is measured by both sunlight and moonlight: perfect for those deep sky astronomers who dislike lunar brightening. More information about this chart and how it was made can be found at the Clear Sky Chart Homepage.