Starguide - A Practical Guide to Astro-Photography

Meteoblue

As an example of a weather or sky condition planning tool you can use Meteoblue (provided by Meteoblue AG, Basel -CH), a tool that provides most of the information you need.

Also check the phase of the moon and the distance between the moon and your target. Unfortunately, our skies are not clear enough to ignore the influence of the moon. Meteoblue helps you to find out if the nights will be dark enough or not. See the example below: next Friday night you can expect 3 relatively dark skies between 20:00 and 23:00, but with some low haze. After the moon rises at 23:19 the sky will be quite lit by the moon and may not allow to take pictures of very faint objects (fainter than mag 5).

Clear Outside

Another useful astronomy weather forecasting tool is Clear Outside (provided by First Light Optics, Exeter, Devon in the UK), also available as app on iOS and Android:

See also the explanations of the term Seeing.

Dark Sky Meter (iOS) or Loss of the Night (Android)

The Dark Sky Meter app (provided by Pocket Science  (brand under DDQ B.V.) measures the sky brightness using the camera and shares it (optionally) with others around the globe. The app can be downloaded from your app store (or play store).

The values reported by the SQM are in units of magnitudes per square arcsecond (mag arcsec−2). Typically, the data provided by SQMs are recorded in magnitudes, denoted as m or mag, specifically in mSQM (or magSQM), where the subscript SQM indicates that the measured radiance is calculated by weighting the electromagnetic radiation according to the spectral sensivity of these instruments.[10] As astronomical magnitudes are on a negative logarithmic scale, smaller values indicate a brighter sky, and a difference of 5 mag arcsec−2 corresponds to a 100-fold difference in luminance. Typical values range from about 16 for bright urban skies to 22 for the darkest skies on Earth.[8] (reference: Wikipedia)  

The main difference between SQM values and the Bortle scale is that Bortle is a tool for an observer to evaluate the specific ambient light conditions at a particular location, whereas SQM measures the actual brightness of the sky, including clouds, haze, and light reflection in the sky, and can vary rapidly with time and the orientation of the measuring device.

See also: Sky Quality Scale (in this guide)

Resources:

• Article: Measuring Night Sky Brightness: Methods and Challenges
• Online brightness map
• Wikipedia article about Sky Quality Meter
• Cloudy Nights discussion about SQM vs. Bortle Scale
• Short Bortle scale defintion

Created with the Personal Edition of HelpNDoc: Elevate Your Documentation Process with HelpNDoc's Advanced Features