There are nine levels of dark space on the Bortle scale:

Bortle 1: Completely dark sky, color base black;

Bortle 2: Typical true dark observation site, color base gray;

Bortle 3: Starry sky in the countryside, color base blue;

Bortle 4: Rural/suburban transition, color base green;

Bortle 5: Suburban sky, color base yellow;

Bortle 6: Bright suburban sky, color base orange;

Bortle 7: Suburban/urban transition, color base red;

Bortle 8: Urban sky, color base white;

Bortle 9: Downtown sky, color base white;

The visibility of celestial objects through a telescope is closely related to atmospheric transparency. To achieve optimal results, it is necessary to go to the dark locations. The commonly used classification for light pollution is the Bortle Scale, where higher numbers indicate higher levels of light pollution. We provide reference sample images for targets observed in different light pollution levels for comparison.

The impact of moonlight on the brightness of the background light in the sky is also very large and can be considered as naturally occurring light pollution, which is scattered by the atmosphere and will be dispersed throughout the sky. There is even a twilight-like effect when the moon is about to rise or just after setting. Therefore, conventional deep space photography should be carried out when the moon is below the horizon, during the period from the 25th to the fifth day of the lunar calendar, the night without the moon is the longest, which is more suitable for deep space photography. We remind everyone to avoid observing or capturing astronomical events during the full moon phase for better observational outcomes.

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