Clear Sky Chart

The image above is a forecast of the quality of astronomical observing for the next two days. The forecast data is generated by the Canadian Meterological Center, and the image above is then generated from that data by a script written by Attilla Danko. The forecast is reasonably accurate for about a 10-mile radius around Fort Smith.

The Arkansas/Oklahoma Astronomical Society is grateful to both the CMC and Mr. Danko for making this forecast available to us.

To read the image:

  1. Check the first row of blocks to determine the cloud cover. Of course, this prediction does not account for things like pop-up thunderstorms, especially in the late afternoon and evening. The darker the blocks, the less cloud cover this indicates.
  2. The second row indicates the transparency of the sky. This helps account for the volume of water vapor in the atmosphere. The darker these blocks are, the more transparent the forecast.
  3. The third row is used to forecast the seeing. The better the seeing, the less turbulence there is in the air. Darker blocks indicate better seeing conditions.
  4. The fourth row, labeled Darkness, not only indicates the hours of daylight an dark, but the influence of the Moon on the hours of darkness. Use this to determine the predicted limiting magnitude based on solar cycles, moon phases, and postiions of both the Sun and Moon. Bear in mind, that certain conditions cannot be calculated into the forecast, such as visual acutiy, topography (i.e. snow-covered landscape,) light pollution, etc.

For more details concerning the clear sky clock, just click on the image and you will be taken to the Clear Sky Chart web site.